File Based Data Processing Systems Vs. Databases

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1 M.SC. (IT) PART-I PAPER : MS(A)-124 RELATIONAL DATABASE MANAGEMENT SYSTEM & ORACLE LESSON NO. 1 Author: Dr. KJS Chowdhary File Based Data Processing Systems Vs. Databases 1 2 Terms Defined: Data, Information File Based Systems 2.1 Advantages of File-Based Approach 2.2 Limitations of File-Based Approach 3 Database Systems 3.1 Advantages offered by Databases 3.2 Disadvantages of Databases 1 Terms Defined: Data, Information The data is the collection of raw facts i.e. the information in an unorganised form. The data may be in the form of alphabets, numeric, images, audio or video. For example, consider the following table: S1 Anu Patiala Arjan Nagar This table clearly states that the independent values S1, Anu, Patiala and Arjan Nagar are all data. The patterns, associations, or relationships among all this data can provide information i.e. the processed form of data is called as information. For example, consider the following table: Srno. Sname Scity Saddress S1 Anu Patiala Arjan Nagar Now if we consider the values S1 as Roll No., Anu as Name, Patiala as City and Arjan Nagar as Address of the Student, it is called as the Information. 2 File Based Systems It is possible to write a list of names, addresses, and phone numbers on a sheet of paper; this is a manual database or a flat file system. This can also be done with any typewriter. A flat file database is the system in which all the information is stored in a plain text file, one database record per line. The data is "flat", as in a sheet of paper. Each record is divided into fields using delimiters or at fixed column positions. This is a Decentralized approach to data management.

2 2 The example of a flat file database is a basic name and address list, where the database consists of a small, fixed number of fields: Name, Address, and Phone Number. Another example is a simple HTML table, consisting of rows and columns. The data has simply been written out in table form as: S.No. Name Address 1 Sandeep 14, Model Town, Jalandhar 2 Satinder 12,Mohni Park, Amritsar 3 Mandeep 24, Nawan Kot, Amritsar 4 Manpreet 38, Ranjeet Nagar, Jalandhar 5 Kawaljeet 28, Arjan Nagar, Patiala Other way to implement the same database is to use "comma-separated" format as: "1","Sandeep","14, Model Town, Jalandhar" "2","Satinder","12, Mohni Park, Amritsar" "3","Mandeep","24, Nawan Kot, Amritsar" "4","Manpreet","38, Ranjeet Naar, Jalandhar" "5","Dr. Kawaljeet","28, Arjan Nagar, Patiala" We could also write it as: 1-Sandeep-14, Model Town, Jalandhar / 2-Satinder-12, Mohni Park, Amritsar / 3Mandeep-24, Nawan Kot, Amritsar / 4-Manpreet-38, Ranjeet Nagar, Jalandhar / 5Dr. Kawaljeet-28, Arjan Nagar, Patiala. All are equivalent databases. We can look at it, we can add new records to it, and we can edit the contents of any field. We can import the entire database into another tool. There is not much we can do with such a simple database. The flat file system is precursor to DBMS. The Microsoft Excel has a simple database tool; it uses the term "list", but this means the same thing as "flat file database". The data is still organized in rows and columns; the field labels are at the top. Clicking a control allows us to sort the database, in this case by S.No. as: 1.1 Advantages of File-Based Approach

3 3 The file-based approach is relatively easy to design and implement since it is normally based on a single application or information system. The processing speed is faster than other ways of storing data. 1.2 Limitations of File-Based Approach Separation and isolation of data o Makes data access difficult. o Each program maintains its own set of data. o Data in different formats. o Users of one program may be unaware of potentially useful data held by other programs. Data redundancy and Inconsistency: o Same information may be duplicated in several places. o All copies may not be updated properly. o Wasted space and potentially different values and/or different formats for the same item. Data Dependence o If you change data format, you need to change all programs that use the file. Incompatible File Formats o Programs are written in different languages, and so cannot easily access each other s files. Fixed Queries o Programs are written to satisfy particular functions. o Any new requirement needs a new program. Security problems o Any user of the system can be able to access any data. 2 Database Systems A Database is traditionally a computerized record-keeping system which can be defined as a collection of logically related data elements that can be stored in a computer in a systematic way which is shared by different applications, can be used simultaneously by many users, designed to meet the information needs of an organization and can easily be accessed, managed and updated by using a computer program. A simple database might be a single file containing many records, each of which contains the same set of fields where each field is a certain fixed width. It may contain a large set of files that are integrated and shareable. The following figure shows a database used by many users:

4 4 A database consists of collection of persistent data (more or less permanent) that is used by the application system of some given enterprise. The term enterprise is a generic term referring to any self-contained commercial, scientific, technical or other organization. An enterprise might be a single individual (with a small private database), or a complete corporation or similar large body (with a very large shared database). The overall purpose is to maintain information and make it available on demand. The information concerned can be anything that is deemed to be of significance to the individual or organization. The system is intended to serve or to assist in the general process of running the business of that individual or organization. The following is an example: Nature of Enterprise A manufacturing company (Large enterprise) A bank (Large enterprise) A hospital (Small enterprise) A university (Medium scale enterprise) A government department (Large enterprise) Nature of Data Product data Account data Patient data Student data Planning data The data maintained in the database by any organization is used for: Routine, highly repetitive applications that were executed over and over again to support the day-to-day operation of the enterprise. Summary information is extracted for the operational database on a periodic basis say once a day or once a week (data being manipulated with the help of mathematical/statistical techniques to generate authentic information). These help an organization in taking important decisions. Generally a database is computerized record keeping system. It is a repository for a collection of computerized data files. The user of the system will be given facilities to perform a variety of operations on such files, such as: Adding new empty files to the database.

5 5 Inserting new data into existing file. Retrieving data from existing file. Updating data in existing files. Deleting data from existing files. Removing existing database files. Consider the following database: RollNo Name Chinu Anu Sumalika Ranjit Amodh Ramandeep Rahul Mandeep Jaswinder Parul City Patiala Patiala Jalandhar Amritsar Ropar Amritsar Kapurthala Jalandhar Jalandhar Jalandhar Sex M F F M M F M F M F Age Percentage Let us look at the basic operations: 1. Retrieving data: Select Name, Age, Sex from STUDENT where city= Jalandhar Result: Name Age Sex Sumalika 21 F Mandeep 20 F Jaswinder 20 M Parul 20 F 2. Inserting new data: Insert into student (Rollno, Name, City, Sex, Age, Percentage) values (11, Timmy, Patiala, M, 40, 86); Result: RollNo. 1 2 Name Chinu Anu City Patiala Patiala Sex M F Age Percentage 73 65

6 Sumalika Ranjit Amodh Ramandeep Rahul Mandeep Jaswinder Parul Timmy Jalandhar Amritsar Ropar Amritsar Kapurthala Jalandhar Jalandhar Jalandhar Patiala F M M F M F M F M Advantages Offered by Databases The advantages offered by databases vary a great deal, depending on their level of sophistication. In general, however, a good database should provide the following advantages over a conventional system: Self-Describing Nature of Database System: complete definition or description of the database structure and constraints are stored in the system catalog and the information stored in the catalog is called meta-data. Independence of Data and Program: This is a prime advantage of a database. Both the database and user program can be altered independently of each other thus saving time and money, which would be required to retain consistency whereas applications are data-dependent in conventional system. This means that the way in which the data is organized in secondary storage and the way in which it is accessed are both dictated by the requirements of the application, and moreover that knowledge of the data organization and access technique is built into the application logic. For example, if a file is stored in indexed sequential form then an application must know that the index exists and the file sequence (as defined by the index). The internal structure of the application will be built around this knowledge. For example, if the file were to be replaced by a hash-addressed file, major modifications would have to be made to the application. Such an application is data-dependent i.e. it is impossible to change the storage structure (how the data is physically recorded) or the access strategy (how it is accessed) without affecting the application, probably drastically. The portions of the application requiring alteration are those that communicate with the file handling software, the difficulties involved are quite irrelevant to the problem the application was written to solve. Data Sharing: The ideal situation is to enable applications to share an integrated database containing all the data needed by the applications and thus eliminate as much as possible the need to store data redundantly.

7 7 Maintenance of Data Integrity: Data integration is generally regarded as an important characteristic of a database. With many different users sharing various portions of the database, the DBMS can maintain the integrity of the database by not allowing more than one user to update the same record at the same time. The DBMS can keep duplicate records out of the database; for example, no two customers with the same customer numbers (key fields) can be entered into the database. Integrity is important in a database system; an application run without validation procedures can produce erroneous data, which can then affect other applications using that data. Centralized Control: With centralized control of database, the DBA can ensure that standards are followed in the representation of data. The Centralized control of the database helps maintain integrity, and permits the DBA to define validation procedures to be carried out whenever any update operation is attempted (update covers modification, creation and deletion). No Data Redundancy: In non-database systems each application has its own private files. This can often lead to redundancy in stored data, with resultant waste in storage space. Redundancy can be direct if a value is a copy of another and indirect if the value can be derived from other values. A Database with uncontrolled redundancy can be in an inconsistent state, it can supply incorrect or conflicting information. In a database the data is integrated. The database may be thought of as a unification of several otherwise distinct data files, with any redundancy among those files partially or wholly eliminated. Performance and Efficiency: In view of the size of databases and of demanding database-accessing requirements, good performance and efficiency are major requirements. Knowing the overall requirements of the organization, as opposed to the requirements of any individual user, the DBA can structure the database system to provide an overall service that is best for the enterprise. Security: Having control over the database, the DBA can ensure that access to the database is through proper channels and can define the access rights of any user to any data items or defined subset of the database. The security system must prevent corruption of the existing data either accidentally or maliciously. Database includes security tools to control access. Data security prevents unauthorized users from viewing or updating the database. Using passwords, users are allowed access to the entire database or subsets of the database, called subschema. For example, an employee database can contain all the data about an individual employee, but one group of users may be authorized to view only payroll data, while others are allowed access to only work history and medical data. 2.2 Disadvantages of Databases

8 8 Confidentiality, Privacy and Security: When information is centralized and is made available to users from remote locations, the possibilities of abuse are often more than in a conventional data processing system. Also there are the chances that unauthorized users may access your important and secret information. While working with DBMS, most databases store valuable information that must be protected against deliberate trespass and destruction. So it is necessary to take technical, administrative and, possibly, legal measures. There is lot of overhead for providing security and recovery functions. Data Quality: Since the database is accessible to users remotely, adequate controls are needed to control users updating data and to control data quality. With increased number of users accessing data directly, there are enormous opportunities for users to damage the data. Unless there are suitable controls, the data quality may be compromised. Data Integrity: Since a large number of users could be using a database concurrently, technical safeguards are necessary to ensure that the data remain correct during operation. The main threat to data integrity comes from several different users attempting to update the same data at the same time. The database therefore needs to be protected against inadvertent changes by the users. Enterprise Vulnerability: Centralizing all data of an enterprise in one database may mean that the database becomes an indispensable resource. The survival of the enterprise may depend on reliable information being available from its database. The enterprise therefore becomes vulnerable to the destruction of the database or to unauthorized modification of the database. High Initial Cost: The cost of DBMS, Computer hardware devices and training to the person employed for using DBMS is very high. High Complexity: A lot to learn to use the Database technology, plus a lot of people are required to manage it. Application Specific: The DBMS is the application specific software, so to use DBMS as per your need you have to develop the software according to your need.

9 9 Exercises Long answer type Questions Question #1 What are file-based systems? What are the various limitations of Flat file system? Question #2 What is a Database? Explain with example. Question #3 What are the advantages offered by databases? Do they have some disadvantages also? If yes, what are those? Fill in the Blanks 1. The is the collection of raw facts. 2. The processed form of data is called as. 3. A is traditionally a computerized record-keeping system. Answers 1. Data 2. Information 3. Database Objective Type Questions 1. The data may be in the form of: a. Alphabets b. Numeric c. Images d. All of the above 2. Which of the following is not the type of data: a. Transactional data b. Non-operational c. Meta data d. Information data 3. Which of the following can provide information: a. Patterns b. Associations c. Relationships d. All of the above 4. Which of the following is not the advantage of File-Based Approach: a. Easy to design b. Easy to implement c. Faster d. High Security

10 10 5. Which of the following is not the disadvantage of database approach: a. Data Quality b. Data Integrity c. Data Redundancy d. High Complexity e. Answers All of the above Information data All of the above High Security Data Redundancy

11 M.SC. (IT) PART-I PAPER : MS(A)-124 RELATIONAL DATABASE MANAGEMENT SYSTEM & ORACLE LESSON NO. 2 Author: Dr. KJS Chowdhary DATABASES DEFINED 1 1. History of Databases 2. Appropriation of Computers for Databases 3. Components of Databases 4. Data vs. Database (Differences between Microsoft Excel and Microsoft Access) 5. Difference between File Based System & Database System History of Databases Ancient to modern: The origins go back to libraries, governmental, business, and medical records. There is a very long history of information storage, indexing, and retrieval. Don't ignore this history; there is usually something to learn from these folks and their success and failure. Lots of online stuff (and there is lots) does not guarantee quality of data or search technique. A good design principle goes way back and lots are known now about how to make good designs that lead to better reliability and performance. 1960's: Computers become cost effective for private companies along with increasing storage capability of computers. Two main data models were developed: network model (CODASYL) and hierarchical (IMS). Access to database is through low-level pointer operations linking records. Storage details depended on the type of data to be stored. Thus, adding an extra field to your database requires rewriting the underlying access/modification scheme. Emphasis was on records to be processed, not overall structure of the system. A user would need to know the physical structure of the database in order to query for information. One major commercial success was SABRE system from IBM and American Airlines : E.F. Codd proposed relational model for databases in a landmark paper on how to think about databases. He disconnects the schema (logical organization) of a database from the physical storage methods. This system has been standard ever since. 1976: P. Chen proposed the Entity-Relationship (ER) model for database design giving yet another important insight into conceptual data models. Such higherlevel modelling allows the designer to concentrate on the use of data instead of logical table structure.

12 12 Early 1980's: Commercialisation of relational systems begins as a boom in DB market for business. Mid-1980's: SQL (Structured Query Language) becomes "intergalactic standard". DB2 becomes IBM's flagship product. Network and hierarchical models fade into the background, with essentially no development of these systems today but some legacy systems are still in use. Development of the IBM PC gives rise to many DB companies and products such as RIM, RBASE 5000, PARADOX, OS/2 Database Manager, Dbase III, IV (later Foxbase, even later Visual FoxPro), Watcom SQL. Early 1990's: An industry shakeout begins with fewer surviving companies offering increasingly complex products at higher prices. Much development during this period centers on client tools for application development such as PowerBuilder (Sybase), Oracle Developer, VB (Microsoft), etc. Client-server model for computing becomes the norm for future business decisions. Development of personal productivity tools such as Excel/Access (MS) and ODBC. This also marks the beginning of Object Database Management Systems (ODBMS) prototypes. Mid-1990's: The usable Internet/WWW appears. A mad scramble ensues to allow remote access to computer systems with legacy data. Client-server reaches the desktop of average users with little patience for complexity while Web/DB grows exponentially. Late-1990's: The large investment in Internet companies fuels tools market boom for Web/Internet/DB connectors. Active Server Pages, Front Page, Java Servlets, JDBC, Enterprise Java Beans, ColdFusion, Dream Weaver, Oracle Developer 2000, etc are examples of such offerings. Open source solution come online with widespread use of gcc, cgi, Apache, MySQL, etc. Online Transaction processing (OLTP) and Online Analytic Processing (OLAP) comes of age with many merchants using Point-Of-Sale (POS) technology on a daily basis. Early 21st century: Decline of the Internet industry as a whole but solid growth of DB applications continues. More interactive applications appear with use of PDAs, POS transactions, consolidation of vendors, etc. Three main (western) companies predominate in the large DB market: IBM (buys Informix), Microsoft, and Oracle. Future trends: Huge (terabyte) systems are appearing and will require novel means of handling and analyzing data. Large science databases such as genome project, geological, national security, and space exploration data. Click-stream analysis is happening now. Data mining, data warehousing, data marts are commonly used techniques today. More of this in the future without a doubt. Smart/personalized shopping using purchase history, time of day, etc. Successors to SQL (and perhaps RDBMS) will be emerging in the future. Most

13 13 attempts to standardize SQL successors have not been successful. SQL92, SQL2, SQL3 are still underpowered and more extensions are hard to agree upon. Most likely this will be overtaken by XML and other emerging techniques. XML with Java for databases is the current poster child of the "next great thing". Check in tomorrow to see what else is news. Mobile database use is a product now coming to market in various ways. Distributed transaction processing is becoming the norm for business planning in many arenas. Probably there will be a continuing shakeout in the RDBMS market. Linux with Apache supporting mysql (or even Oracle) on relatively cheap hardware is a major threat to high cost legacy systems of Oracle and DB2 so these have begun pre-emptive projects to hold onto their customers. Object Oriented Everything, including databases, seems to be always on the verge to sweeping everything before it. Object Database Management Group (ODMG) standards are proposed and accepted and maybe something comes from that. Ethical/security/use issues tend to be diminished at times but always come back. Should you be able to consult a database of the medical records/genetic makeup of a prospective employee? Should you be able to screen a prospective partner/lover for genetic diseases? Should amazon.com keep track of your book purchasing? Should there be a national database of convicted sex offenders/violent criminals/drug traffickers? Who is allowed to do Web tracking? How many times in the last six months did you visit a particular sex chat room/porn site/political satire site? Who should be able to keep or view such data? Who makes these decisions? 2. Appropriation of Computers for Databases The computers are more suited for database applications because of many reasons as attributed below: 1. Speed, Accuracy, Reliability, Diligence and Versatility of computers make computer an ideal computing machine to maintain databases: a. It can perform various operations such as searching for the required information, sorting the information in desired order, calculating results and printing reports in the desired format within fraction of seconds. b. It can work day-in and day out. c. A computer can do the work in one day what the human can do in his entire lifetime. d. Computer is very accurate device, which can give the results without any error. The errors can occur in computers but these are mainly due to human rather than technological weakness i.e. due to improper instruction by the user or due to inaccurate data.

14 14 2. Unlike human beings a computer is free from monotony, tiredness, lack of concentration etc., so the computers can work for hours together without creating any error. 3. Option of number of mass storage devices available with computers allow storage of voluminous data in a most cost-effective manner and for a longer duration 4. Modern day Information and Communication Technologies with the help of Internet allows databases residing on computers to be distributed and shareable. 3. Components of Databases Data, Software, Hardware and Users are the key components of databases as shown in following figure: 1. Data: The data (plural; datum: singular) are the collection of raw facts, observations chronologically recoded. The data may be in the form of alphabets, numeric, images, audio or video. The supreme philosophy of organising data in the form of database is keep one data at one place. Therefore, the data in databases must ensure two essential properties: a. Integrated: The Data, which does not have any redundancy, is called as the integrated data. The 100% Integration is not possible. Hence it should be at minimal level. b. Shared: The data, which is shared among several users and applications of an organization (in the sense that each user and/or application may have access to that data), is called as the shared data. 2. Hardware: The hardware consists of the computer system used for accessing and storing the database. It can be mainframe, network or personal computer. The secondary storage devices such as Hard disk, floppy disks and CD-ROM of the computer system are used for storing the databases. 3. Software: The software is the layer between the user and the computer. All of the interaction of user with computer can be made with the help of software. The DBMS, operating system, network software (if necessary) and also the application programs are examples of software used in DBMS. 4. Users: The users are the persons that can have to work on computers with the help of the software. The following are the various types of users: I. Application programmers: The application programmers are the programmers who are responsible for developing the application software or

15 II. III. IV. V. 15 programs that provide functionality for the users. These are computer professionals interacting with the system through Data Manipulation Language. Sophisticated users: These users interact with the system without writing programs. These users know more about the database language and skills. They form requests by writing queries in a database query language, which are submitted to a query processor. Naive users: These are unsophisticated users who interact with the system by using permanent application programs (e.g. Automated Teller Machine). These users don't know anything about database and don't need to know. For example, the clerk in a store who uses bar code readers don t need to know anything about the database whereas the business manager know the structure of the database and may perform their own queries and programs. Data Administrator: The Data Administrator is the person that manages the data resource. The Data Administrator can have to plan the conceptual/logical design, works with senior manager and has knowledge of business rules. Database Administrator: The Database Administrator (DBA) is a person having centralized control over the data and programs. The DBA can have to implement and manage physical database design, operation, configuration, performance security and data integrity. The DBA's are more technical than a Data Administrator. A DBA directs or performs all activities related to maintaining a successful database environment with keeping the database operating smoothly, ensuring that backups are done on a regular basis, and installing new software. The responsibilities of DBA include planning, designing, implementing, and maintaining the database system; establishing policies and procedures pertaining to the management, disk space needs, security, maintenance, adding users and use of the database management system; and training employees in database management. Sometimes the roles are combined.

16 16 4. Data vs. Database (Differences between Microsoft Excel and Microsoft Access) Excel (Data) Access (Database) Flat File (rows and columns) Tables (rows and columns) Calculations (field based) Graphs, etc Queries (based on tables) Relationships (between tables) Rules (unique values, etc) Updating functions (table based) Reports (based on tables, queries) 5. File Based System vs. Database System File Based System Database System In a file processing system, the system stores permanent records in various files. Application programs are needed to extract and add records to the appropriate files. As time passes new files and corresponding application programs are added to the system. In a database system, there exists a collection of inter-related files and a set of application programs to access and modify these files. Details of data storage and maintenance are hidden from users. Supported by conventional operating systems such as MS-DOS. A database may be generated automatically or it may be computerized. The computerized database may be created and maintained by a database management system. Since different programmers create the files and application programs over a long period of time, data in the files are likely to get repeated. Redundancy can lead to inconsistency i.e. the various copies of the same data may contain different information. A database system so designed does not involve the problem of data redundancy or inconsistency. Not every user of the system should be able to access all the data. In a file processing system, since application A database system so designed provides the security mechanisms to prevent unwanted users from accessing certain

17 17 programs are added in an ad-hoc manner, it is difficult to enforce such security constraints. parts or whole of the database. For example, tellers in a bank see only that part of the database that has information on customer accounts. They cannot access information about salaries of employees. Multiple user access to the information is difficult to provide through the conventional file processing system, this is due to the use of the application programs, which have not been coordinated previously. Almost all the database systems allow multiple users to update database at the same time. Exercises Long Answer Type Questions Question #1 Why computers are suited most for databases? Question #2 Why would you choose a database system instead of simply storing data in operating system files? When would it make sense not to use a database system? Question #3 What are the various components of databases? Briefly explain each. Question #3 Compare the performance of flat file systems and databases. Fill in the Blanks 1. The consists of the computer system used for accessing and storing the database. 2. The users don't know anything about database and don't need to know. 3. The is the person that manages the data resource. 4. In a there exists a collection of inter-related files and a set of application programs to access and modify these files. Answers 1. Hardware 2. Naive 3. Data Administrator 4. Database system

18 18 Objective Type Questions 1. Which of the following is not a component of databases? a. Data b. Integrity c. Software d. Hardware 2. P. Chen proposed the Entity-Relationship (ER) model for database design in: a b c d The computers are more suited for database applications because of which reason: 1. Speed 2. Reliability 3. Versatility 4. All of the above 4. Which of the following is a person having centralized control over the data and programs. a. Database Administrator b. Data Administrator c. Sophisticated user d. Application programmer Answers Integrity 1976 All of the above Database Administrator

19 M.Sc. (IT) PART-I LESSON NO. 3 PAPER : MS(A)-124 RELATIONAL DATABASE MANAGEMENT SYSTEM & ORACLE Author: Dr. KJS Chowdhary DATABASE ADMINISTRATOR & TERMINOLOGY OF DATABASES 1. Database Administrator 1.1 Responsibilities of the Database Administrator 2. Terms Defined: Entity Entity set Attribute/Field Record Tuple Cardinality Database File Database Schema Database Instance Universe of Discourse 3. Software Modules to protect Accuracy of Database Database Administrator The database administrator is a person having centralized control over the database. The DBA can have to implement and manage physical database design, operation, configuration, performance, security and data integrity. The DBA's are more technical than a Data Administrator. A database administrator (DBA) directs or performs all activities related to maintaining a successful database environment with keeping the database operating smoothly, ensuring that backups are done on a regular basis, and installing new software. The responsibilities of DBA include planning, designing, implementing, and maintaining the database system; establishing policies and procedures pertaining to the management, disk space needs, security, maintenance, adding users and training employees in database management to use database management system. Sometimes the roles are combined. 1.1 Responsibilities of the Database Administrator Deciding the Information Content of the Database: Identifying the entities of interest to the enterprise and the information to be recorded about those entities. This is defined by writing the conceptual schema using the Data Definition Language. Scheme Definition: The creation of the original database scheme. This involves writing a set of definitions in a DDL (Data Definition Language), and converts these into a set of tables stored in the data dictionary. Deciding the Storage Structure and Access Strategy: How the data is to be represented by writing the storage structure definition. The associated internal/conceptual schema must also be specified using the DDL 1.

20 20 Scheme and Physical Organization Modification: Writing a set of definitions used by the DDL compiler to generate modifications to appropriate internal system tables (e.g. data dictionary). This is done rarely, but sometimes the database scheme or physical organization must be modified. Generating Integrity Constraints: The database manager module consults these whenever updates occur. Liaison with Users: To ensure that the data they require is available and to write the necessary external schemas and conceptual/external mapping by using DDL. Backup and Recovery: Perhaps the most important responsibility of the DBA is protecting the data in the system. To effectively do this, you must develop an effective backup and recovery strategy and make sure it is carried out. A DBA's chief responsibility is to maintain the integrity of the database. It is important that the backup and recovery process be periodically tested. For example, periodic dumping of the database to a backup tape and procedures for reloading the database for backup. Use of a log file where each log record contains the values for database items before and after a change and can be used for recovery purposes. Security Administration: One of the main duties of the DBA is to monitor and administer DBMS security. This involves adding and removing users, administering quotas, auditing, and checking for security problems. Performance Tuning and Monitoring: The DBA must continually monitor system performance and be prepared to retune the system as necessary. Even a well-tuned system must be constantly monitored and adjusted. Sometimes this involves changing tuning parameters, other times this involves rebuilding an index or restructuring a table. Defining Authorization Checks and Validation Procedures for Data Access: Authorization checks and validation procedures are extensions to the conceptual schema and can be specified using the DDL i.e. Granting different types of authorization for data access to various users. Responding to Changes in Requirements: Changing details of storage and access thereby organizing the system so as to get the performance that is best for the enterprise. Installation of New Software: It is primarily the job of the DBA to install new versions of Oracle software, application software, and other software related to DBMS administration. It is important that the DBA or other information system staff members test this new software before it is moved into a production environment. Configuration of Hardware and Software with System Administrator: In many cases the system administrator can only access the system software. In this case, - -

21 21 the DBA must work closely with the system administrator to perform software installations, and to configure hardware and software so that it functions optimally with the DBMS. Routine Scheduled Maintenance: It is the job of the DBA to schedule routine DBMS maintenance and carry out this maintenance. This maintenance is regularly carried out in the early hours of the morning or on weekends when this maintenance causes the least inconvenience to the user community. Troubleshooting: In the event of a system or DBMS failure, it is the job of the DBA to troubleshoot or assist in troubleshooting of the problem. The DBA might also participate in or lead the effort to find and eliminate problems. Failure Recovery: Because a system failure can mean that the users do not have access to their data, it can be the job of the DBA to lead efforts to recover from system failures. The well-prepared DBA has contingency plans for system outages and can soon have the DBMS running again. Some of the more additional duties of the DBA might include the following: Data analysis: The DBA will frequently be called on to analyse the data stored in the database and to make recommendations relating to performance and efficiency of that data storage. This might relate to the more effective use of indexes or the use of some feature such as the Parallel Query option. Database design (preliminary): The DBA is often involved at the preliminary database-design stages. Through the involvement of the DBA, many problems that might occur can be eliminated. The DBA knows the DBMS and system, can point out potential problems, and can help the development team with special performance considerations. Data Modelling and Optimisation: By modelling the data, it is possible to optimise the system layout to take the advantage of your I/O subsystem. Assisting developers with SQL and stored procedure development--the DBA should be prepared to be a resource for developers and users. The DBA is often called on to help with SQL problems as well as to design and write stored procedures. Enterprise Standards and Naming Conventions: Because many different groups might perform different roles in developing and deploying applications, it is often the DBA who is called on to help define enterprise standards and naming conventions as well as to ensure that new applications are conforming to these standards. Development of production migration procedures: Because the DBA is responsible for the availability and reliability of the DBMS and applications using that DBMS, it is up to the DBA to develop and maintain procedures for rolling out new applications and DBMS software. This involves evaluating new software or - -

22 22 patches as well as testing them. It is up to the DBA to guarantee the stability and robustness of the system. Environmental documentation: The DBA should document every aspect of the DBMS environment, including hardware configuration and maintenance records, software updates, changes to the applications and DBMS, and all other items related to changes made to the system. The DBA should be able to access these records and fully reproduce the current system as necessary. Consult with development team and end users: The DBA is often called on to act as a consultant to the development team as well as to the user community. This might involve personally assisting a single user or developing training courses for the user community as a whole. Evaluation of new software: The DBA might be called on to evaluate new software and make recommendations based on that evaluation. This might be related to a software purchase or a scheduled rollout of a new version of software. This evaluation must be done in the context of the stability of the system. Evaluation of new hardware: There is much consideration involved in purchasing new hardware and software. Much of this consideration involves the functionality and compatibility of the software or hardware as well as the cost of these components. Although the cost of the item is not usually a concern of the DBA, but the functionality and compatibility is. The DBA might be asked to make recommendations based on whether these purchases make sense. Capacity planning and sizing: Determining whether it is necessary to purchase new hardware or software to meet increased loads is often a job for the DBA. Capacity planning and sizing is important to provide the level of service your users require. By anticipating the future needs of your users, you can provide an excellent level of service with no interruptions. 2. Terms Defined Entity: An item (person, place, object, event or concept) of interest is called as the Entity. The term entity by itself is often used to express either of these concepts but you can usually infer the intended meaning from the context in which the term is used. In the following example Suppliers and Parts are entities. Order is a relation between two entities. - -

23 Entity set: A set of entities of the same type is called as entity set. For example all of the account entities and a person entity for a bank are in both the customer and employee sets. Attribute / Field: An Attribute/Field is an abstraction characteristic of an entity or a relation. It is the smallest unit of data to which a name can be assigned; it can be thought of as a column in a table. Example: The attributes that describe entity Supplier are: Supplier name, Address, Age, City etc. Record: A collection of related fields is called as a row or record in a table. Tuple: The tuple is the formal name for a row in a relation/table. Cardinality: The number of rows in the table is called as the cardinality. Database File: A database file is a structure used to store data about some entity. Such a file can be thought of as a table. [Attributes/ Fields] Sno* Sname Scity Saddress [Records] S1 Anu [data] Patiala Arjan Nagar S2 Chinu Patiala Preet Nagar S3 Sumalika Jalandhar Urban Estate S4 Amoth Ropar Jawahar Nagar S5 Ranjit Amritsar University Campus [A Database File] Supplier [Entity] 23 Database Schema: The structural description or logical layout of the type of facts held in the database is called as the schema. The schema describes the collection of objects that are represented in the database, and the relationships that exist between these objects. - -

24 24 Supplier Sno* S1 S2 S3 S4 S5 Schema Sname Scity Saddress Database Instance Anu Patiala Arjan Nagar Chinu Patiala Preet Nagar Sumalika Jalandhar Urban Estate Amoth Ropar Jawahar Nagar Ranjit Amritsar University Campus Database Instance: The information in a database at a particular point in time is called an instance of the database. Each database instance has a database name and consists of volumes, all the files in the run directory, and a collection of metadata (including configuration data, database parameters, and volume paths). Universe of Discourse: The term "universe of discourse" generally refers to the entire set of terms used in a specific discourse, i.e. the family of linguistic or semantic terms that are specific to any one area of interest. In model-theoretical semantics, the term "universe of discourse" refers to the set of entities that a model is based on. 3. Software Modules to protect Accuracy of Database The DBMS (Database Management System) is the mediator between the database and the users. It allows the users to communicate with the users. Using the software modules the DBMS controls access to data and helps maintain the consistency of the data. DBMS uses three software modules: Data dictionary Run-time manager Stored data manager The data dictionary is accessed to verify that if the request sent by the user to the database is legal for that particular database. For example, if the user wants all the parts that are red in colour then the attribute colour must actually exist within the table of that database. The run-time manager then processes the actual queries, Retrieves the requested information or updates the tables. The stored data manager, accessed by the DBA, may use the functions of the operating system or may handle tasks on its own. It also keeps the data dictionary up to date as instructed by the DDL. Exercises - -

25 25 Long Answer Type Questions Question #1 Who is a DBA? What are his various jobs and responsibilities? Also give the additional duties that may be assigned to DBA. Question #2 What are the various Software Modules used to protect the Accuracy of Database? Question #3 Give some of the additional duties that the DBA may perform. Question #4 Give the differences between the following: Entity & Entity set Database instance & Database Schema Fill in the Blanks 1. The is a person having centralized control over the database. 2. An item (person, place, object, event or concept) of interest is called as 3. A set of entities of the same type is called as 4. A is a structure used to store data about some entity. 5. A collection of related fields is called as a in a table. 6. The number of rows in the table is called as the. 7. The structural description or logical layout of the type of facts held in the database is called as the. 8. The information in a database at a particular point in time is called an of the database. Answers Database administrator Entity Entity set Database file Record Cardinality Database Schema Instance Objective Type Questions - -

26 26 1. The DBA can have to implement and manage: a. Physical database design b. Performance c. Security d. All of the above 2. Which of the following is not the responsibility of DBA: a. Scheme Definition b. Entering data into database c. Designing the database d. Maintaining the database 3. Which of the following is not a software module: a. Data dictionary b. Data station c. Run-time manager d. Stored data manager Answers 1. All of the above 2. Entering data into database 3. Data station - -

27 M.Sc. (IT) PART-I PAPER : MS(A)-124 RELATIONAL DATABASE MANAGEMENT SYSTEM & ORACLE LESSON NO. 4 Author: Dr. KJS Chowdhary CONCEPTS OF DBMS Data Base Management System Functions of a DBMS Types of Database Management Systems Advantages of DBMS approach Disadvantages of DBMS approach Components of DBMS DBMS (Database Management System) It is a software system that enables users to define, create, and maintain the database and which provides controlled access to the database. In other words, It is the software package, which is designed to manipulate the data in database on behalf of a user i.e. it controls the organization, storage and retrieval of data in a database. It also controls the security and integrity of the database i.e. it ensures the integrity of the data and prevents the user or program for attempting to access the data from needing to know the physical location of the data on the disk. It consists of collection of interrelated and persistent data (usually referred to as the database). The DBMS accepts requests for data from the application program and instructs the operating system to transfer the appropriate data. They are widely used in business applications. The goal of a DBMS is to provide an environment that is both convenient and efficient to use in retrieving information from the database and storing information into the database. Organizations may use one kind of DBMS for daily transaction processing and then move the detail onto another computer that uses another DBMS better suited for random inquiries and analysis. 2 Functions of a DBMS Data Storage, Retrieval, and Update. A User-Accessible Catalogue. Transaction Support. Concurrency Control Services. Recovery Services. Authorization Services. Support for Data Communication. Integrity Services. Services to Promote Data Independence. Utility Services.

28 3 28 Types of Database Management Systems Enterprise DBMS: It is designed for scalability and high performance. It must be capable of supporting very large databases, a large number of concurrent users, and multiple types of applications. The enterprise DBMS will run on a large-scale machine, typically a mainframe or a high-end Unix, Linux, or Windows NT machine. Furthermore, an enterprise DBMS offers all of the bells and whistles available from the DBMS vendor. Support for Multi-processor, parallel queries, clustering, and other advanced DBMS features will be core components of an enterprise DBMS. Summeriziing we can say that: o Databases or set of databases to serve an entire organization. o May be distributed over several different physical locations. o Requires organizational standards for system development and maintenance. Departmental DBMS: Sometimes referred to as a workgroup DBMS, supports small to medium sized workgroups within an organization, and typically runs on Unix, Linux, or Windows 2000 (or NT) server. Hardware and software upgrades often can allow a departmental DBMS to tackle tasks that previously could only be performed by an enterprise DBMS. Summerizing we can say that: o A functional area (such as production) in a firm. o Same hardware/software as Workgroup database, but is specialized for the department. Personal DBMS: It is designed to be used by a single user, typically on a low- to medium-powered PC platform. Lotus, Microsoft Access and dbase are examples of personal database software. Of course, the major DBMS vendors also market personal versions of their more high-powered solutions, Personal Oracle and DB2 for example. Sometimes the low cost of a personal DBMS causes misguided attempts to choose a personal DBMS for a departmental or enterprise solution. But do not be lured by the low cost. A personal DBMS product is suited only for small-scale projects and should not be used to deploy multi-user applications. Summerizing we can say that: o Supports a single-user. o Stand-alone. o May purchase such an application from a vendor. o Can t integrate data with other applications. Mobile DBMS: It is a specialized version of a departmental or enterprise DBMS. It is designed to be used by remote users. The mobile DBMS enables local database access and modification on a laptop or handheld device, such as a Palm PDA or PocketPC. Furthermore, the mobile DBMS provides a mechanism for synchronizing remote database changes to a centralized enterprise or departmental database server.

29 4 29 Advantages of DBMS approach Redundancies and Inconsistencies can be Reduced: The data in conventional data systems is often not centralised. Some applications may require data to be combined from several systems. These several systems could well have data that is redundant as well as inconsistent (that is, different copies of the same data may have different values). Data inconsistencies are often encountered in everyday life. But the DBMS is often centralized, so by using DBMS approach you can easily reduce the redundancies as well as inconsistencies. Better Service to the Users: In conventional systems, availability of information is often poor since it normally difficult to obtain information that the existing systems were not designed for. Once several conventional systems are combined to form one centralised data base, the availability of information is likely to improve since the data can now be shared and the DBMS makes it easy to respond to unforeseen information requests. Centralizing the data in a database also often means that users can obtain new and combined information that would have been impossible to obtain otherwise. Also, use of a DBMS should allow users that do not know programming to interact with the data more easily. The ability to quickly obtain new and combined information is becoming increasingly important in an environment where various levels of governments are requiring organisations to provide more and more information about their activities. An organisation running a conventional data processing system would require new programs to be written (or the information compiled manually) to meet every new demand. Flexibility of the System is Improved: Changes are often necessary to the contents of data stored in any system. These changes are more easily made in a database than in a conventional system in that these changes do not need to have any impact on application programs. Cost of Developing and Maintaining Systems is Lower: Although the initial cost of setting up of a database can be large, one normally expects the overall cost of setting up a database and developing and maintaining application programs to be lower than for similar service using conventional systems since the productivity of programmers can be substantially higher in using non-procedural languages that have been developed with modern DBMS than using procedural languages. Standards can be Enforced: Since all access to the database must be through the DBMS, standards are easier to enforce. Standards may relate to the naming of the data, the format of the data, the structure of the data etc. Security can be Improved: Setting up of a database makes it easier to enforce security restrictions since the data is now centralized. It is easier to control that

30 30 which person has access to what parts of the database. However, setting up a database can also make it easier for a determined person to breach security. Integrity can be Improved: Integrity may be compromised in many ways. For example, someone may make a mistake in data input and the salary of a full-time employee. A student may be shown to have borrowed books but has no enrolment. Salary of a staff member in one department may be coming out of the budget of another department. Controls therefore must be introduced to prevent such errors to occur. However, since all data is stored only once, it is often easier to maintain integrity than in conventional systems. Enterprise Requirements can be Identified: All enterprises have sections and departments and each of these units often consider the work of their unit as most important and therefore consider their needs as most important. Once a database has been set up with centralised control, it will be necessary to identify enterprise requirements and to balance the needs of competing units. It may become necessary to ignore some requests for information if they conflict with higher priority needs of the enterprise. Data Model must be Developed: Perhaps the most important advantage of setting up a database system is the requirement that an overall data model for the enterprise be built. In conventional systems, it is more likely that files will be designed as needs of particular applications demand. The overall view is often not considered. Building an overall view of the enterprise data, although often an expensive exercise is usually very cost-effective in the long term. 5 Disadvantages of DBMS approach A database system generally provides on-line access to the database for many users. In contrast, a conventional system is often designed to meet a specific need and therefore generally provides access to only a small number of users. Because of the larger number of users accessing the data when a database is used, the enterprise may involve additional risks as compared to a conventional data processing system in the following areas. Confidentiality, Privacy and Security: When information is centralised and is made available to users from remote locations, the possibilities of abuse are often more than in a conventional data processing system. To reduce the chances of unauthorised users accessing sensitive information, it is necessary to take technical, administrative and, possibly, legal measures. Most databases store valuable information that must be protected against deliberate trespass and destruction. Data Quality: Since the database is accessible to users remotely, adequate controls are needed to control users updating data and to control data quality. With increased number of users accessing data directly, there are enormous

31 6 31 opportunities for users to damage the data. Unless there are suitable controls, the data quality may be compromised. Data Integrity: Since a large number of users could be using a database concurrently, technical safeguards are necessary to ensure that the data remain correct during operation. The main threat to data integrity comes from several different users attempting to update the same data at the same time. The database therefore needs to be protected against inadvertent changes by the users. Enterprise Vulnerability: Centralising all data of an enterprise in one database may mean that the database becomes an indispensable resource. The survival of the enterprise may depend on reliable information being available from its database. The enterprise therefore becomes vulnerable to the destruction of the database or to unauthorised modification of the database. The Cost of using a DBMS: Conventional data processing systems are typically designed to run a number of well-defined, pre-planned processes. Such systems are often "tuned" to run efficiently for the processes that they were designed for. Although the conventional systems are usually fairly inflexible in that new applications may be difficult to implement and/or expensive to run, they are usually very efficient for the applications they are designed for. The database approach on the other hand provides a flexible alternative where new applications can be developed relatively inexpensively. The flexible approach is not without its costs and one of these costs is the additional cost of running applications that the conventional system was designed for. Using standardised software is almost always fewer machines efficient than specialised software. Physical data independence: It is the ability to modify the physical structure without making it necessary to rewrite application programs. Such modifications include changing from unblocked to blocked record storage, or from sequential to random access files. Components of DBMS Database Manager/Engine: It is a program module which provides the interface between the low-level data stored in the database and the application programs and queries submitted to the system. Its responsibilities include: Interaction with the file manager: storing, retrieving and updating of data in the database. Integrity enforcement: checking for conditions. Security enforcement: enforcing constraints on the users. Backup and recovery. Concurrency Control.

32 32 File Manager: A computer program that provides a user interface to work with file systems is called as the file manager. It may be a general purpose file system provided by the underlying OS or it may be a specialized file system that knows about the particular ways in which the data of the database is stored. Similar to Microsoft Windows Explorer in function, the File Manager Option in the Control Panel allows you to perform file management tasks such as creating files and directories, setting the read, write or execute permissions on the files and directories in your site, renaming or deleting files or directories, and changing the password for directories that are password-protected. The most common operations on files are: create, open, edit, view, print, play, rename, move, copy, delete, attributes, properties, search/find, and permissions. Typically files are displayed in a hierarchy. Security Utilities: The security utilities are used to secure many databases from unauthorized access. Any unauthorized user may damage your data from the database. The DBMS must be responsible for establishing and maintaining security access controls. Security component of DBMS must identify the user and then provide or limit access to various parts of the database. Various administrative utilities such as backup and recovery, user management, data storage, evaluation and performance monitoring tools are provided with most of the DBMSs. Disk Manager: Disk Manager is a graphical tool used for managing disks, volumes and controlling access to the information that is stored on the disk. It supports partitions, logical drives, new dynamic volumes, and remote disk management. The data is transferred from main memory to the disk with the help of disk manager. Query Processor: The query processor is used for handling the queries. The queries are analysed and executed by generating calls to the database engine. Data and Data files: The data files are the physical data structures where user data is stored. One or more data files form Tablespaces. One data file can be associated with only one table space. Communication System: The communication system is the system with the help of which you can communicate with the databases located at remote places. Data Dictionary: A catalogue of all data held in a database, or a list of items giving data names and structures is called as a data dictionary i.e. centralized repository of information about the stored data, providing details of its meaning, relationship (to other data), origin, usage and format is called as a data dictionary. The data dictionary contains information about tables, indexes, clusters, and so on. It stores information about the structure of the database. Data dictionary information includes database elements and valid values used to

33 33 describe datasets. A Data Dictionary is a repository for descriptions of data types or object types. The Data Dictionaries are used to store definitions of, for example, item types and their attributes. This allows users to see what item types have been defined and what their uses are. Active data dictionaries are used by software to validate data as it is entered and to provide users with access to definitions on-line. Data dictionary is a tool used in database management systems to track the tables, fields, field names, field lengths, default settings, validation rules, and relationships. This is a file that defines a file's structure, to include a file's fields and relationship to other files. This is sometimes called schema. Data dictionaries maintain facilities to document data elements, records, programs, systems, files, users, and other system components. A dictionary will also have facilities to cross-reference all system components to each other. The data dictionary may be considered a database in its own right. A data dictionary contains a list of all files in the database, the number of records in each file, and the names and types of each field. Most database management systems keep the data dictionary hidden from users to prevent them from accidentally destroying its contents. In relational databases, the data dictionary is the system table that describes the organization of data in a particular database. Commercial RDBMSs have online data dictionaries stored in special tables called system tables. Data dictionaries do not contain any actual data from the database, only book keeping information for managing it. Without a data dictionary, however, a database management system cannot access data from the database. Data dictionaries are sometimes simply a collection of database columns and the definitions of what the meaning and types the columns contain i.e. data dictionary is set of metadata that contains definitions and representations of data elements. Data dictionaries are one step along a pathway of creating precise semantic definitions for an organization. Within the context of a DBMS, a data dictionary is a read-only set of tables and views. The data dictionary may be considered a database in its own right. Among other things, a data dictionary holds the following information: Precise definition of data elements. Usernames, roles and privileges. Schema objects. Integrity constraints. Stored procedures and triggers. General database structure. Audit information. Space allocations. The following are some characteristics of Data Dictionary:

34 34 One benefit of a well-prepared data dictionary is a consistency between data items across different tables. For example, several tables may hold telephone numbers; using a data dictionary the format of this telephone number field will be consistent. When an organization builds an enterprise-wide data dictionary it may include both semantics and representational definitions for data elements. The semantic components focus on creating precise meaning of data elements. Representation definitions include how data elements are stored in a computer structure such as an integer, string or date format. Data dictionaries are more precise then glossaries (terms and definitions) because they frequently have one or more representations of how data is structured. Data dictionaries are usually separate from data models since data models usually include complex relationships between data elements. Exercises Long Answer Type Questions Question #1 What is Data Base Management System? What are the various functions of DBMS? Question #2 Give the differences between Enterprise & Departmental DBMS. Question #3 What are the various advantages of DBMS approach? Do they have any disadvantages? If so also explain the disadvantages. Question #4 What are the various components of DBMS? Question #5 What is a Data Dictionary? What purpose does it serve? Give the characteristics of Data Dictionary. Fill in the Blanks 1. The is the software package, which is designed to manipulate the data in database. 2. The is a program module which provides the interface between the low-level data and the application programs and queries submitted to the system. Answers 1. DBMS 2. Database Manager

35 35 Objective Type Questions 1. Which of the following is not an advantage of DBMS? a. Independence of data and program b. Maintenance of data integrity c. Data Quality d. Security 2. Which of the following is not a component of DBMS? a. Data b. Database Engine c. Query Processor d. Data Dictionary 3. Which of the following is not a function of DBMS: a. Data Cleaning b. Data Storage c. Retrieval d. Update 4. Which of the following is the type of Database Management Systems: a. Enterprise DBMS b. Personal DBMS c. Mobile DBMS d. Landline DBMS 5. A computer program that provides a user interface to work with file systems is called as: a. File Manager b. Database Manager c. Security Utilities d. Disk Manager Answers Data Quality Data Data Storage Landline DBMS File Manager

36 M.Sc. (IT) PART-I LESSON NO. 5 PAPER : MS(A)-124 RELATIONAL DATABASE MANAGEMENT SYSTEM & ORACLE Author: Dr. KJS Chowdhary ANSI/ SPARC Architecture of DBMS 1 DBMS/ANSI-SPARC Architecture 1.1 Physical or Internal Level 1.2 Conceptual Level 1.3 View/External Level 2 Data Independence 2.1 Logical Data Independence 2.2 Physical Data Independence 3. Client/Server Systems 3.1 Characteristics of Client/Server Architectures 3.2 Advantages of using Client/Server 3.3 Disadvantages of using Client/Server 1 DBMS/ANSI-SPARC Architecture The three-level architecture suggested by ANSI/SPARC (American National Standards Institute/Standards Planning and Requirements Committee) was produced first in 1972 followed by a final report in The reports proposed an architectural framework for databases having three distinct levels at which data items can be described. Under this approach, a database is considered as containing data about an enterprise. The major purpose of a database system is to provide users with an abstract view of the system, which means that the system hides certain details of how data is stored, created and maintained. The three level database architecture allows a clear separation of the information meaning (conceptual view) from the external data representation and from the physical data structure layout. The architecture for DBMS is divided into three general levels: Physical or Internal Level: Physical representation of the database i.e. how the data are stored. Lowest level of abstraction. DBMS and operating system level. Complex low-level structures described in detail. Conceptual Level: Next highest level of abstraction. Provides the mapping between the external and internal levels Describes what data are stored.

37 37 Doesn t contain any storage dependent details, such as number of bytes. Describes the relationships among data. Database administrator level. View/External Level: Highest level. Describes part of the database for a particular group of users. Can be many different views of a database. E.g. Automatic Teller Machines in a bank get a view of customer accounts, but not of payroll data. The objective of the three-level architecture is to separate the users view(s) of the database from the way that it is physically represented. This is desirable for the following reasons: It allows independent customized user views i.e. each user should be able to access the same data, but have a different customized view of the data. These should be independent: changes to one view should not affect others. It hides the physical storage details for users i.e. users should not have to deal with physical database storage details. They should be allowed to work with the data itself, without concern for how it is physically stored. The database administrator should be able to change the database storage structures without affecting the users views. From time to time rationalizations or other changes to the structure of an organization s data will be required. The internal structure of the database should be unaffected by changes to the physical aspects of the storage. For example, a changeover to a new disk. The database administrator should be able to change the conceptual or global structure of the database without affecting the users. This should be possible while still maintaining the desired individual users views. The following figure shows the architecture for DBMS:

38 Physical or Internal Level/Schema The internal level is concerned with the way in which the data is actually stored. The internal level is concerned with allocating storage space for data and indexes, describing the forms that records will take when stored, and record placement, assembling records into files and data compression and encryption techniques. The internal view is a low-level representation of the entire database consisting of multiple occurrences of multiple types of internal (stored) records. It describes how the data is stored in the database in terms of particular data structures and file organizations. It does not deal in terms of physical records/blocks or with any device specific constraints such as cylinder or track sizes. Details of mapping to physical storage are highly implementation specific and are not expressed in the three-level architecture. The internal view described by the internal schema that defines the various types of stored records, how stored fields are represented and in which physical sequence the records are stored. 1.2 Conceptual Level/Schema In conceptual level the user view a formal description of data of interest to the organization, independent of any storage considerations. This level contains the logical structure of the entire database. This view is normally more stable than the other two views. With the help of conceptual level you can view the data as it actually is. The conceptual level represents all entities, their attributes, and their relationships, the constraints on the data, security and integrity information. It consists of multiple occurrences of multiple types of conceptual record, defined in the conceptual schema. In addition to definitions, the conceptual schema contains authorization and validation procedures. The Storage structure, Access strategy is ignored in this level.

39 View/External Level/Schema The external level is concerned with the way individual users see the data. It describes the part of the database that is relevant to a particular user. The views in this level may display data in different formats or combine data from several entities. Views may provide different representations of the same data. For example, some users might view dates in the form (day/month/year) while others prefer (year/month/day). Some views might include derived or calculated data. For example, a person s age might be calculated from their date of birth since storing their age would require it to be updated each year. This view is often a restricted view of the database and the same database may provide a number of different views for different classes of users. The user is anyone who needs to access some portion of the data. They may range from application programmers to casual users with limited queries. Each user has a language at his/her disposal. The application programmer may use a high level language like Visual Basic, while the casual user will probably use a query language. For example, large organizations may have finance and stock control departments. Workers in finance will not usually view stock details, as they are more concerned with the accounting side of things. Thus, workers in each department will require a different user interface to the information stored in the database. Regardless of the language used, it will include a Data Sub Language (DSL) that is the subset of the language, which is concerned with storage and retrieval of information in the database and may or may not be apparent to the user. A DSL is a combination of two languages: Data Definition Language (DDL) that provides the definition or description of database objects. Data Manipulation Language (DML) that provides the manipulation or processing of database objects. 2 Data Independence The database is the collection of data that is persistent in nature. It should be integrated and shared. It was strongly felt that the management of data is easier when the DBMS software is separate from the actual data. The ability to modify a scheme definition in one level without affecting a scheme definition in a higher level is called data independence. It is important to maintain data independence in a database so that different users can concurrently use it and feel confident that the DBMS is maintaining integrity and accuracy of data. The data independence can be achieved at the following two levels: Physical Data Independence: At the physical level, the DBA (Database Administrator) should able to change the internal structure of a database without altering the community or the external views. The physical data independence is

40 40 related to the actual storage of data on storage medium. The way the data are stored in bits and bytes should not affect user s access to that data. Modifications at this level are done to improve performance. Logical Data Independence: The ability to modify the conceptual scheme without causing application programs to be rewritten. Usually done when logical structure of database is altered. Logical data independence is harder to achieve, as the application programs are usually heavily dependent on the logical structure of the data. An analogy is made to abstract data types in programming languages. However, it is difficult to achieve 100% data independence practically. DBAs ensure that during design process utmost care must be taken to achieve it the maximum level. 3. Client/Server Systems Client/server computing is the logical extension of modular programming. Modular programming has its fundamental assumption that separation of a large piece of software into its constituent parts creates the possibility for easier development and better maintainability. Client/server computing takes this a step farther by recognizing that those modules need not be executed within the same memory space. With this architecture, the calling module becomes the "client" (that requests a service), and the called module becomes the "server" (that provides the service). The logical extension of this is to have clients and servers running on the appropriate hardware and software platforms for their functions.

41 41 From a high-level point of view, a database system can be regarded as having a very simple two-part structure, consisting of a server (also called the backend) and a set of clients (also called front-ends). In a client/server system (which is generally called as the centralized system), the entire database would reside on one server at one central location. This (server) system is a special machine that is ideally suited for database applications. In other words, it supports fast I/O operations, have large amount of secondary memory to store huge databases, bigger main memory and sophisticate software to ensure proper security measures (essential for integrity) of a database. The Server is just the DBMS itself. It supports all of the basic DBMS functions data definition, data manipulation, data security and integrity, and so on. In particular, it provides all of the external, conceptual, and internal level support. Thus the server in this context is just another name for the DBMS. The clients are the various applications that run on top of the DBMS-both user written applications and built-in applications, i.e., applications provided by the DBMS vendor or by some third party.