Topic 1: Database System Concept

Transcription

1 Topic 1: Database System Concept Purpose of Database Management Systems Organizations use large amounts of data. A database management system (DBMS) is a software tool that makes it possible to organize data in a database. The standard acronym for database management system is DBMS, so you will often see this instead of the full name. The ultimate purpose of a database management system is to store and transform data into information to support making decisions. A DBMS consists of the following three elements: 1. The physical database: the collection of files that contain the data 2. The database engine: the software that makes it possible to access and modify the contents of the database 3. The database scheme: the specification of the logical structure of the data stored in the database While it sounds logical to have a DBMS in place, it is worth thinking for a moment about the alternative. What would the data in an organization look like without a DBMS? Consider yourself as the organization for a moment, and the data are all the files on your computer. How is your data organized? If you are like most typical computer users, you have a large number of files, organized in folders. You may have word processor documents, presentation files, spreadsheets, photographs, etc. You find the information you need based on the folder structure you have created and the names you have given to your files. This is called a file system and is typical for individual computer users. Now consider the challenges you are faced with. Have you ever lost a file? Have you had difficulty finding a file? Probably. Perhaps you are using multiple computers and your files are located in different physical locations. And when was the list time you created a backup of all your files? You do back up, right? You probably get the picture. A file system is relatively simple, but it only works if you keep yourself very organized and disciplined. Now consider an organization with 1,000 employees, each with their own computer. Can you see some of the challenges when using a file system? Do you really want critical financial data floating around the offices as simple files on individual computers? Functions of a DBMS So what does a DBMS really do? It organizes your files to give you more control over your data. A DBMS makes it possible for users to create, edit and update data in database files. Once created, the DBMS makes it possible to store and retrieve data from those database files. 1

2 More specifically, a DBMS provides the following functions: Concurrency: concurrent access (meaning 'at the same time') to the same database by multiple users Security: security rules to determine access rights of users Backup and recovery: processes to back-up the data regularly and recover data if a problem occurs Integrity: database structure and rules improve the integrity of the data Data descriptions: a data dictionary provides a description of the data Within an organization, the development of the database is typically controlled by database administrators (DBAs) and other specialists. This ensures the database structure is efficient and reliable. Database administrators also control access and security aspects. For example, different people within an organization use databases in different ways. Some employees may simply want to view the data and perform basic analysis. Other employees are actively involved in adding data to the database or updating existing data. This means that the database administrator needs to set the user permissions. You don't want someone who only needs to view the database to accidentally delete parts of the database. Advantages of the DBMS: The DBMS serves as the intermediary between the user and the database. The database structure itself is stored as a collection of files, and the only way to access the data in those files is through the DBMS. The DBMS receives all application requests and translates them into the complex operations required to fulfill those requests. The DBMS hides much of the database s internal complexity from the application programs and users. The different advantages of DBMS are as follows. 1. Improved data sharing. The DBMS helps create an environment in which end users have better access to more and better-managed data. Such access makes it possible for end users to respond quickly to changes in their environment. 2. Improved data security. The more users access the data, the greater the risks of data security breaches. Corporations invest considerable amounts of time, effort, and money to ensure that corporate data are used properly. A DBMS provides a framework for better enforcement of data privacy and security policies. 2

3 3. Better data integration. Wider access to well-managed data promotes an integrated view of the organization s operations and a clearer view of the big picture. It becomes much easier to see how actions in one segment of the company affect other segments. 4. Minimized data inconsistency. Data inconsistency exists when different versions of the same data appear in different places. For example, data inconsistency exists when a company s sales department stores a sales representative s name as Bill Brown and the company s personnel department stores that same person s name as William G. Brown, or when the company s regional sales office shows the price of a product as $45.95 and its national sales office shows the same product s price as $ The probability of data inconsistency is greatly reduced in a properly designed database. 5. Improved data access. The DBMS makes it possible to produce quick answers to ad hoc queries. From a database perspective, a query is a specific request issued to the DBMS for data manipulation for example, to read or update the data. Simply put, a query is a question, and an ad hoc query is a spur-of-the-moment question. The DBMS sends back an answer (called the query result set) to the application. For example, end users, when dealing with large amounts of sales data, might want quick answers to questions (ad hoc queries) such as: What was the dollar volume of sales by product during the past six months? What is the sales bonus figure for each of our salespeople during the past three months? How many of our customers have credit balances of $3,000 or more? 6.Improved decision making. Better-managed data and improved data access make it possible to generate better-quality information, on which better decisions are based. The quality of the information generated depends on the quality of the underlying data. Data quality is a comprehensive approach to promoting the accuracy, validity, and timeliness of the data. While the DBMS does not guarantee data quality, it provides a framework to facilitate data quality initiatives. 7.Increased end-user productivity. The availability of data, combined with the tools that transform data into usable information, empowers end users to make quick, informed decisions that can make the difference between success and failure in the global economy. 3

4 Disadvantages of Database: Although the database system yields considerable advantages over previous data management approaches, database systems do carry significant disadvantages. For example: 1. Increased costs. Database systems require sophisticated hardware and software and highly skilled personnel. The cost of maintaining the hardware, software, and personnel required to operate and manage a database system can be substantial. Training, licensing, and regulation compliance costs are often overlooked when database systems are implemented. 2. Management complexity. Database systems interface with many different technologies and have a significant impact on a company s resources and culture. The changes introduced by the adoption of a database system must be properly managed to ensure that they help advance the company s objectives. Given the fact that database systems hold crucial company data that are accessed from multiple sources, security issues must be assessed constantly. 3. Maintaining currency. To maximize the efficiency of the database system, you must keep your system current. Therefore, you must perform frequent updates and apply the latest patches and security measures to all components. Because database technology advances rapidly, personnel training costs tend to be significant. Vendor dependence. Given the heavy investment in technology and personnel training, companies might be reluctant to change database vendors. As a consequence, vendors are less likely to offer pricing point advantages to existing customers, and those customers might be limited in their choice of database system components. 4. Frequent upgrade/replacement cycles. DBMS vendors frequently upgrade their products by adding new functionality. Such new features often come bundled in new upgrade versions of the software. Some of these versions require hardware upgrades. Not only do the upgrades themselves cost money, but it also costs money to train database users and administrators to properly use and manage the new features. 4

5 What is RDBMS? RDBMS stands for Relational Database Management System. RDBMS is the basis for SQL, and for all modern database systems like MS SQL Server, IBM DB2, Oracle, MySQL, and Microsoft Access. A Relational database management system (RDBMS) is a database management system (DBMS) that is based on the relational model as introduced by E. F. Codd. STRUCTURE OF DBMS DBMS (Database Management System) acts as an interface between the user and the database. The user requests the DBMS to perform various operations (insert, delete, update and retrieval) on the database. The components of DBMS perform these requested operations on the database and provide necessary data to the users. The various components of DBMS are shown below: - 1. DDL Compiler - Data Description Language compiler processes schema definitions specified in the DDL. It includes metadata information such as the name of the files, data items, storage details of each file, mapping information and constraints etc. 2. DML Compiler and Query optimizer - The DML commands such as insert, update, delete, retrieve from the application program are sent to the DML compiler for compilation into object code for database access. The object code is then optimized in the best way to execute a query by the query optimizer and then send to the data manager. 3. Data Manager - The Data Manager is the central software component of the DBMS also knows as Database Control System. The Main Functions Of Data Manager Are: Convert operations in user's Queries coming from the application programs or combination of DML Compiler and Query optimizer which is known as Query Processor from user's logical view to physical file system. Controls DBMS information access that is stored on disk. It also controls handling buffers in main memory. 5

6 It also enforces constraints to maintain consistency and integrity of the data. It also synchronizes the simultaneous operations performed by the concurrent users. It also controls the backup and recovery operations. 4. Data Dictionary - Data Dictionary is a repository of description of data in the database. It contains information about Data - names of the tables, names of attributes of each table, length of attributes, and number of rows in each table. Relationships between database transactions and data items referenced by them which is useful in determining which transactions are affected when certain data definitions are changed. Constraints on data i.e. range of values permitted. Detailed information on physical database design such as storage structure, access paths, files and record sizes. Access Authorization - is the Description of database users their responsibilities and their access rights. Usage statistics such as frequency of query and transactions. Data dictionary is used to actually control the data integrity, database operation and accuracy. It may be used as a important part of the DBMS. Data Dictionary is necessary in the databases due to following reasons: It improves the control of DBA over the information system and user's understanding of use of the system. It helps in documentating the database design process by storing documentation of the result of every design phase and design decisions. It helps in searching the views on the database definitions of those views. It provides great assistance in producing a report of which data elements (i.e. data values) are used in all the programs. It promotes data independence i.e. by addition or modifications of structures in the database application program are not effected. 5. Data Files - It contains the data portion of the database. 6. Compiled DML - The DML complier converts the high level Queries into low level file access commands known as compiled DML. 7. End Users - They are already discussed in previous section. Database Architecture Database architecture is logically divided into two types. 1. Logical two-tier Client / Server architecture 2. Logical three-tier Client / Server architecture 6

7 Two-tier Client / Server Architecture Two-tier Client / Server architecture is used for User Interface program and Application Programs that runs on client side. An interface called ODBC(Open Database Connectivity) provides an API that allow client side program to call the dbms. Most DBMS vendors provide ODBC drivers. A client program may connect to several DBMS's. In this architecture some variation of client is also possible for example in some DBMS's more functionality is transferred to the client including data dictionary, optimization etc. Such clients are called Data server. Three-tier Client / Server Architecture 7

8 Three-tier Client / Server database architecture is commonly used architecture for web applications. Intermediate layer called Application server or Web Server stores the web connectivty software and the business logic(constraints) part of application used to access the right amount of data from the database server. This layer acts like medium for sending partially processed data between the database server and the client. Data Mining: What is Data Mining? Generally, data mining (sometimes called data or knowledge discovery) is the process of analyzing data from different perspectives and summarizing it into useful information - information that can be used to increase revenue, cuts costs, or both. Data mining software is one of a number of analytical tools for analyzing data. It allows users to analyze data from many different dimensions or angles, categorize it, and summarize the relationships identified. Technically, data mining is the process of finding correlations or patterns among dozens of fields in large relational databases. Data, Information, and Knowledge Data Data are any facts, numbers, or text that can be processed by a computer. Today, organizations are accumulating vast and growing amounts of data in different formats and different databases. This includes: operational or transactional data such as, sales, cost, inventory, payroll, and accounting nonoperational data, such as industry sales, forecast data, and macro economic data meta data - data about the data itself, such as logical database design or data dictionary definitions Information The patterns, associations, or relationships among all this data can provide information. For example, analysis of retail point of sale transaction data can yield information on which products are selling and when. Knowledge Information can be converted into knowledge about historical patterns and future trends. For example, summary information on retail supermarket sales can be analyzed in light of promotional efforts to provide knowledge of consumer buying behavior. Thus, a manufacturer or retailer could determine which items are most susceptible to promotional efforts. 8

9 Data Warehouses Dramatic advances in data capture, processing power, data transmission, and storage capabilities are enabling organizations to integrate their various databases into data warehouses. Data warehousing is defined as a process of centralized data management and retrieval. Data warehousing, like data mining, is a relatively new term although the concept itself has been around for years. Data warehousing represents an ideal vision of maintaining a central repository of all organizational data. Centralization of data is needed to maximize user access and analysis. Dramatic technological advances are making this vision a reality for many companies. And, equally dramatic advances in data analysis software are allowing users to access this data freely. The data analysis software is what supports data mining. Disadvantages of file processing 1. Data Mapping and Access: - Although all the related informations are grouped and stored in different files, there is no mapping between any two files. i.e.; any two dependent files are not linked. Even though Student files and Student_Report files are related, they are two different files and they are not linked by any means. Hence if we need to display student details along with his report, we cannot directly pick from those two files. We have to write a lengthy program to search Student file first, get all details, then go Student_Report file and search for his report. 9

10 When there is very huge amount of data, it is always a time consuming task to search for particular information from the file system. It is always an inefficient method to search for the data. 2. Data Redundancy: - There are no methods to validate the insertion of duplicate data in file system. Any user can enter any data. File system does not validate for the kind of data being entered nor does it validate for previous existence of the same data in the same file. Duplicate data in the system is not appreciated as it is a waste of space, and always lead to confusion and mishandling of data. When there are duplicate data in the file, and if we need to update or delete the record, we might end up in updating/deleting one of the record, leaving the other record in the file. Again the file system does not validate this process. Hence the purpose of storing the data is lost. Though the file name says Student file, there is a chance of entering staff information or his report information in the file. File system allows any information to be entered into any file. It does not isolate the data being entered from the group it belongs to. 3. Data Dependence: - In the files, data are stored in specific format, say tab, comma or semicolon. If the format of any of the file is changed, then the program for processing this file needs to be changed. But there would be many programs dependent on this file. We need to know in advance all the programs which are using this file and change in the entire place. Missing to change in any one place will fail whole application. Similarly, changes in storage structure, or accessing the data, affect all the places where this file is being used. We have to change it entire programs. That is smallest change in the file affect all the programs and need changes in all them. 4. Data inconsistency: - Imagine Student and Student_Report files have student s address in it, and there was a change request for one particular student s address. The program searched only Student file for the address and it updated it correctly. There is another program which prints the student s report and mails it to the address mentioned in the Student_Report file. What happens to the report of a student whose address is being changed? There is a mismatch in the actual address and his report is sent to his old address. This mismatch in different copies of same data is called data inconsistency. This has occurred here, because there is no proper listing of files which has same copies of data. 10

11 5. Data Isolation: - Imagine we have to generate a single report of student, who is studying in particular class, his study report, his library book details, and hostel information. All these informations are stored in different files. How do we get all these details in one report? We have to write a program. But before writing the program, the programmer should find out which all files have the information needed, what is the format of each file, how to search data in each file etc. Once all these analysis is done, he writes a program. If there is 2-3 files involved, programming would be bit simple. Imagine if there is lot many files involved in it? It would be require lot of effort from the programmer. Since all the datas are isolated from each other in different files, programming becomes difficult. 6. Security: - Each file can be password protected. But what if have to give access to only few records in the file? For example, user has to be given access to view only their bank account information in the file. This is very difficult in the file system. 7. Integrity: - If we need to check for certain insertion criteria while entering the data into file it is not possible directly. We can do it writing programs. Say, if we have to restrict the students above age 18, then it is by means of program alone. There is no direct checking facility in the file system. Hence these kinds of integrity checks are not easy in file system. 8. Atomicity: - If there is any failure to insert, update or delete in the file system, there is no mechanism to switch back to the previous state. Imagine marks for one particular subject needs to be entered into the Report file and then total needs to be calculated. But after entering the new marks, file is closed without saving. That means, whole of the required transaction is not performed. Only the totaling of marks has been done, but addition of marks not being done. The total mark calculated is wrong in this case. Atomicity refers to completion of whole transaction or not completing it at all. Partial completion of any transaction leads to incorrect data in the system. File system does not guarantee the atomicity. It may be possible with complex programs, but introduce for each of transaction costs money. 9. Concurrent Access: - Accessing the same data from the same file is called concurrent access. In the file system, concurrent access leads to incorrect data. For example, a student wants to borrow a book from the library. He searches for the book in the library file and sees that only one copy is available. At the same time another student also, wants to borrow same book and checks that one copy available. First student opt 11

12 for borrow and gets the book. But it is still not updated to zero copy in the file and the second student also opt for borrow! But there are no books available. This is the problem of concurrent access in the file system. The principal advantages of DBMS over file processing system: Flexibility: Because programs and data are independent, programs do not have to be modified when types of unrelated data are added to or deleted from the database, or when physical storage changes. Fast response to information requests: Because data is integrated into a single database, complex requests can be handled much more rapidly than locating data separately. In many businesses, faster response means better customer service. Multiple access: Database software allows data to be accessed in a variety of ways (through various key fields), by using several programming languages (both3gl and nonprocedural4gl programs). Lower user training costs: Users often find it easier to learn such systems and training costs may be reduced. Also, the total time taken to process requests may be less, which would increase user productivity. Less storage: Theoretically, all occurrences of data items need be stored only once, thereby eliminating the storage of redundant data. System developers and database designers often use data normalization to minimize data redundancy. Here are some disadvantages: DBMS subjects business to risk of critical data loss in its electronic format and can be more readily stolen without proper security. The cost of a DBMS can be prohibitive for small enterprises as they struggle with cost justification for making investment in the infrastructure. Improper use of the DBMS can lead to incorrect decision making as people take presented data for granted as accurate. Data can be stolen by weak password security policy. 12

13 Database Management System (DBMS) and Its Applications: A Database management system is a computerized record-keeping system. It is a repository or a container for collection of computerized data files. The overall purpose of DBMS is to allow he users to define, store, retrieve and update the information contained in the database on demand. Information can be anything that is of significance to an individual or organization. Databases touch all aspects of our lives. Some of the major areas of application are as follows: 1. Banking 2. Airlines 3. Universities 4. Manufacturing and selling 5. Human resources Uses of DBMS: Data that is well organized and integrated is very useful in decision making. Thus, we can infer some of the following uses of DBMS: (i) Effective and efficient management of data (ii) Query processing and management (iii) Easy to understand and user friendly (iv) Security and integrity of data (v) Better Decision making 13

14 (vi) Data sharing and storage (vii) Better access to accurate data (viii) Ensures error free information What is RDBMS? Explain its features. RDBMS stands for Relational Database Management System. It organizes data into related rows and columns. Features: - It stores data in tables. - Tables have rows and column. - These tables are created using SQL. - And data from these tables are also retrieved using SQL. What is RDBMS? Explain its features. RDBMS is a database management system based on relational model defined by E.F.Codd. Data is stored in the form of rows and columns. The relations among tables are also stored in the form of the table. Features: - Provides data to be stored in tables - Persists data in the form of rows and columns - Provides facility primary key, to uniquely identify the rows - Creates indexes for quicker data retrieval - Provides a virtual table creation in which sensitive data can be stored and simplified query can be applied.(views) - Sharing a common column in two or more tables(primary key and foreign key) - Provides multi user accessibility that can be controlled by individual users. Difference between DBMS and RDBMS Although DBMS and RDBMS both are used to store information in physical database but there are some remarkable differences between them. 14

15 The main differences between DBMS and RDBMS are given below: No. DBMS RDBMS 1) DBMS applications store data as file. RDBMS applications store data in a tabular form. 2) In DBMS, data is generally stored in either In RDBMS, the tables have an identifier called a hierarchical form or a navigational form. primary key and the data values are stored in the form of tables. 3) Normalization is not present in DBMS. Normalization is present in RDBMS. 4) DBMS does not apply any security with RDBMS defines the integrity constraint for the regards to data manipulation. purpose of ACID (Atomocity, Consistency, Isolation and Durability) property. 5) DBMS uses file system to store data, so in RDBMS, data values are stored in the form of there will be no relation between the tables, so arelationship between these data tables. values will be stored in the form of a table as well. 6) DBMS has to provide some uniform RDBMS system supports a tabular structure of methods to access the stored information. the data and a relationship between them to access the stored information. 7) DBMS does not support distributed RDBMS supports distributed database. database. 8) DBMS is meant to be for small organization RDBMS is designed to handle large amount of and deal with small data. it supports single data. it supportsmultiple users. user. 9) Examples of DBMS are file Example of RDBMS are mysql, postgre, sql systems, xml etc. server, oracle etc. 15

16 Database Software Systems 1. Oracle RDBMS 2. IBM DB2 3. Microsoft SQL Server 4. SAP Sybase ASE 5. Teradata 7. MySQL 9. Microsoft Access List of relational database management systems 4th Dimension Adabas D Alpha Five Apache Derby Aster Data Amazon Aurora Altibase CA Datacom CA IDMS Clarion Data Abstraction For the system to be usable, it must retrieve data efficiently. The need for efficiency has led designers to use complex data structures to represent data in the database. Since many databasesystems users are not computer trained, developers hide the complexity from users through several levels of abstraction, to simplify users interactions with the system: Physical Level : The lowest level of abstraction describes how the data are actually stored. The physical level describes complex low-level data structures in detail. Logical Level : The next-higher level of abstraction describes what data are stored in the database, and what relationships exist among those data. The logical level thus describes 16

17 the entire database in terms of a small number of relatively simple structures. Although implementation of the simple structures at the logical level may involve complex physical-level structures, the user of the logical level does not need to be aware of this complexity. Database administrators, who must decide what information to keep in the database, use the logical level of abstraction. View Level : The highest level of abstraction describes only part of the entire database. Even though the logical level uses simpler structures, complexity remains because of the variety of information stored in a large database. Many users of the database system do not need all this information; instead, they need to access only a part of the database. The view level of abstraction exists to simplify their interaction with the system. The system may provide many views for the same database. Database Languages DDL For describing data and data structures a suitable description tool, a data definition language (DDL), is needed. With this help a data scheme can be defined and also changed later. Typical DDL operations (with their respective keywords in the structured query language SQL): Creation of tables and definition of attributes (CREATE TABLE...) Change of tables by adding or deleting attributes (ALTER TABLE ) Deletion of whole table including content (!) (DROP TABLE ) DML Additionally a language for the descriptions of the operations with data like store, search, read, change, etc. the so-called data manipulation, is needed. Such operations can be done with a data manipulation language (DML). Within such languages 17

18 keywords like insert, modify, update, delete, select, etc. are common. Typical DML operations (with their respective keywords in the structured query language SQL): Add data (INSERT) Change data (UPDATE) Delete data (DELETE) Query data (SELECT) Database Schema A database schema is the skeleton structure that represents the logical view of the entire database. It defines how the data is organized and how the relations among them are associated. It formulates all the constraints that are to be applied on the data. A database schema defines its entities and the relationship among them. It contains a descriptive detail of the database, which can be depicted by means of schema diagrams. It s the database designers who design the schema to help programmers understand the database and make it useful. 18

19 A database schema can be divided broadly into two categories Physical Database Schema This schema pertains to the actual storage of data and its form of storage like files, indices, etc. It defines how the data will be stored in a secondary storage. Logical Database Schema This schema defines all the logical constraints that need to be applied on the data stored. It defines tables, views, and integrity constraints. Database Instance It is important that we distinguish these two terms individually. Database schema is the skeleton of database. It is designed when the database doesn't exist at all. Once the database is operational, it is very difficult to make any changes to it. A database schema does not contain any data or information. A database instance is a state of operational database with data at any given time. It contains a snapshot of the database. Database instances tend to change with time. A DBMS ensures that its every instance (state) is in a valid state, by diligently following all the validations, constraints, and conditions that the database designers have imposed. Data Independence A database system normally contains a lot of data in addition to users data. For example, it stores data about data, known as metadata, to locate and retrieve data easily. It is rather difficult to modify or update a set of metadata once it is stored in the database. But as a DBMS expands, it needs to change over time to satisfy the requirements of the users. If the entire data is dependent, it would become a tedious and highly complex job. 19

20 Metadata itself follows a layered architecture, so that when we change data at one layer, it does not affect the data at another level. This data is independent but mapped to each other. Logical Data Independence Logical data is data about database, that is, it stores information about how data is managed inside. For example, a table (relation) stored in the database and all its constraints, applied on that relation. Logical data independence is a kind of mechanism, which liberalizes itself from actual data stored on the disk. If we do some changes on table format, it should not change the data residing on the disk. Physical Data Independence All the schemas are logical, and the actual data is stored in bit format on the disk. Physical data independence is the power to change the physical data without impacting the schema or logical data. For example, in case we want to change or upgrade the storage system itself suppose we want to replace hard-disks with SSD it should not have any impact on the logical data or schemas. 20

21 Components of a DBMS The DBMS accepts the SQL commands generated from a variety of user interfaces, produces query evaluation plans, executes these plans against the database, and returns the answers. As shown, the major software modules or components of DBMS are as follows: (i) Query processor: The query processor transforms user queries into a series of low level instructions. It is used to interpret the online user's query and convert it into an efficient series of operations in a form capable of being sent to the run time data manager for execution. The query processor uses the data dictionary to find the structure of the relevant portion of the database and uses this information in modifying the query and preparing and optimal plan to access the database. (ii) Run time database manager: Run time database manager is the central software component of the DBMS, which interfaces with user-submitted application programs and queries. It handles database access at run time. It converts operations in user's queries coming. Directly via the query processor or indirectly via an application program from the user's logical view to a physical file system. It accepts queries and examines the external and conceptual schemas to determine what conceptual records are required to satisfy the user s request. It enforces constraints to maintain the consistency and integrity of the data, as well as its security. It also performs backing and recovery operations. Run time database manager is sometimes referred to as the database control system and has the following components: Authorization control: The authorization control module checks the authorization of users in terms of various privileges to users. Command processor: The command processor processes the queries passed by authorization control module. 21

22 Integrity checker: It.checks the integrity constraints so that only valid data can be entered into the database. Query optimizer: The query optimizers determine an optimal strategy for the query execution. Transaction manager: The transaction manager ensures that the transaction properties should be maintained by the system. Scheduler: It provides an environment in which multiple users can work on same piece of data at the same time in other words it supports concurrency. (iii) Data Manager: The data manager is responsible for the actual handling of data in the database. It provides recovery to the system which that system should be able to recover the data after some failure. It includes Recovery manager and Buffer manager. The buffer manager is responsible for the transfer of data between the main memory and secondary storage (such as disk or tape). It is also referred as the cache manger. 22

23 Execution Process of a DBMS As show, conceptually, following logical steps are followed while executing users to request to access the database system: (I) Users issue a query using particular database language, for example, SQL commands. (ii) The passes query is presented to a query optimizer, which uses information about how the data is stored to produce an efficient execution plan for the evaluating the query. (iii) The DBMS accepts the users SQL commands and analyses them. (iv) The DBMS produces query evaluation plans, that is, the external schema for the user, the corresponding external/conceptual mapping, the conceptual schema, the conceptual/internal mapping, and the storage structure definition. Thus, an evaluation\ plan is a blueprint for evaluating a query. (v) The DBMS executes these plans against the physical database and returns the answers to the user. Using components such as transaction manager, buffer manager, and recovery manager, the DBMS supports concurrency and recovery. Database Users Database users are the one who really use and take the benefits of database. There will be different types of users depending on their need and way of accessing the database. 1. Application Programmers - They are the developers who interact with the database by means of DML queries. These DML queries are written in the application programs like C, C++, JAVA, Pascal etc. These queries are converted into object code to communicate with the database. For example, writing a C program to generate the report of employees who are working in particular department will involve a query to fetch the data from database. It will include a embedded SQL query in the C Program. 2. Sophisticated Users - They are database developers, who write SQL queries to select/insert/delete/update data. They do not use any application or programs to request the database. They directly interact with the database by means of query language like SQL. These users will be scientists, engineers, analysts who thoroughly study SQL and DBMS to apply the concepts in their requirement. In short, we can say this category includes designers and developers of DBMS and SQL. 23

24 3. Specialized Users - These are also sophisticated users, but they write special database application programs. They are the developers who develop the complex programs to the requirement. 4. Stand-alone Users - These users will have stand alone database for their personal use. These kinds of database will have readymade database packages which will have menus and graphical interfaces. 5. Native Users - these are the users who use the existing application to interact with the database. For example, online library system, ticket booking systems, ATMs etc which has existing application and users use them to interact with the database to fulfill their requests. Database Administrators A DBA has many responsibilities. A good performing database is in the hands of DBA. Installing and upgrading the DBMS Servers: - DBA is responsible for installing a new DBMS server for the new projects. He is also responsible for upgrading these servers as there are new versions comes in the market or requirement. If there is any failure in upgradation of the existing servers, he should be able revert the new changes back to the older version, thus maintaining the DBMS working. He is also responsible for updating the service packs/ hot fixes/ patches to the DBMS servers. Design and implementation: - Designing the database and implementing is also DBA s responsibility. He should be able to decide proper memory management, file organizations, error handling, log maintenance etc for the database. Performance tuning: - Since database is huge and it will have lots of tables, data, constraints and indices, there will be variations in the performance from time to time. Also, because of some designing issues or data growth, the database will not work as expected. It is responsibility of the DBA to tune the database performance. He is responsible to make sure all the queries and programs works in fraction of seconds. Migrate database servers: - Sometimes, users using oracle would like to shift to SQL server or Netezza. It is the responsibility of DBA to make sure that migration happens without any failure, and there is no data loss. 24

25 Backup and Recovery: - Proper backup and recovery programs needs to be developed by DBA and has to be maintained him. This is one of the main responsibilities of DBA. Data/objects should be backed up regularly so that if there is any crash, it should be recovered without much effort and data loss. Security: - DBA is responsible for creating various database users and roles, and giving them different levels of access rights. Documentation: - DBA should be properly documenting all his activities so that if he quits or any new DBA comes in, he should be able to understand the database without any effort. He should basically maintain all his installation, backup, recovery, security methods. He should keep various reports about database performance. Types of DBA Administrative DBA - This DBA is mainly concerned with installing, and maintaining DBMS servers. His prime tasks are installing, backups, recovery, security, replications, memory management, configurations and tuning. He is mainly responsible for all administrative tasks of a database. Development DBA - He is responsible for creating queries and procedure for the requirement. Basically his task is similar to any database developer. Database Architect - Database architect is responsible for creating and maintaining the users, roles, access rights, tables, views, constraints and indexes. He is mainly responsible for designing the structure of the database depending on the requirement. These structures will be used by developers and development DBA to code. Data Warehouse DBA -DBA should be able to maintain the data and procedures from various sources in the datawarehouse. These sources can be files, COBOL, or any other programs. Here data and programs will be from different sources. A good DBA should be able to keep the performance and function levels from these sources at same pace to make the datawarehouse to work. Application DBA -He acts like a bridge between the application program and the database. He makes sure all the application program is optimized to interact with the database. He ensures all the activities from installing, upgrading, and patching, maintaining, backup, recovery to executing the records works without any issues. 25

26 OLAP DBA - He is responsible for installing and maintaining the database in OLAP systems. He maintains only OLAP databases. DBMS - Architecture 3-tier Architecture A 3-tier architecture separates its tiers from each other based on the complexity of the users and how they use the data present in the database. It is the most widely used architecture to design a DBMS. Database (Data) Tier At this tier, the database resides along with its query processing languages. We also have the relations that define the data and their constraints at this level. Application (Middle) Tier At this tier reside the application server and the programs that access the database. For a user, this application tier presents an abstracted view of the database. End-users are unaware of any existence of the database beyond the application. At the other end, the database tier is not aware of any other user beyond the 26

27 application tier. Hence, the application layer sits in the middle and acts as a mediator between the end-user and the database. User (Presentation) Tier End-users operate on this tier and they know nothing about any existence of the database beyond this layer. At this layer, multiple views of the database can be provided by the application. All views are generated by applications that reside in the application tier. Characteristics Traditionally, data was organized in file formats. DBMS was a new concept then, and all the research was done to make it overcome the deficiencies in traditional style of data management. A modern DBMS has the following characteristics Real-world entity A modern DBMS is more realistic and uses real-world entities to design its architecture. It uses the behavior and attributes too. For example, a school database may use students as an entity and their age as an attribute. Relation-based tables DBMS allows entities and relations among them to form tables. A user can understand the architecture of a database just by looking at the table names. Isolation of data and application A database system is entirely different than its data. A database is an active entity, whereas data is said to be passive, on which the database works and organizes. DBMS also stores metadata, which is data about data, to ease its own process. Less redundancy DBMS follows the rules of normalization, which splits a relation when any of its attributes is having redundancy in values. Normalization is a mathematically rich and scientific process that reduces data redundancy. Consistency Consistency is a state where every relation in a database remains consistent. There exist methods and techniques, which can detect attempt of leaving database in inconsistent state. A DBMS can provide greater consistency as compared to earlier forms of data storing applications like file-processing systems. Query Language DBMS is equipped with query language, which makes it more efficient to retrieve and manipulate data. A user can apply as many and as different filtering options as required to retrieve a set of data. Traditionally it was not possible where file-processing system was used. 27

28 ACID Properties DBMS follows the concepts of Atomicity,Consistency, Isolation, and Durability (normally shortened as ACID). These concepts are applied on transactions, which manipulate data in a database. ACID properties help the database stay healthy in multi-transactional environments and in case of failure. Multiuser and Concurrent Access DBMS supports multi-user environment and allows them to access and manipulate data in parallel. Though there are restrictions on transactions when users attempt to handle the same data item, but users are always unaware of them. Multiple views DBMS offers multiple views for different users. A user who is in the Sales department will have a different view of database than a person working in the Production department. This feature enables the users to have a concentrate view of the database according to their requirements. Security Features like multiple views offer security to some extent where users are unable to access data of other users and departments. DBMS offers methods to impose constraints while entering data into the database and retrieving the same at a later stage. DBMS offers many different levels of security features, which enables multiple users to have different views with different features. For example, a user in the Sales department cannot see the data that belongs to the Purchase department. Additionally, it can also be managed how much data of the Sales department should be displayed to the user. Since a DBMS is not saved on the disk as traditional file systems, it is very hard for miscreants to break the code. Users A typical DBMS has users with different rights and permissions who use it for different purposes. Some users retrieve data and some back it up. The users of a DBMS can be broadly categorized as follows 28

29 Administrators Administrators maintain the DBMS and are responsible for administrating the database. They are responsible to look after its usage and by whom it should be used. They create access profiles for users and apply limitations to maintain isolation and force security. Administrators also look after DBMS resources like system license, required tools, and other software and hardware related maintenance. Designers Designers are the group of people who actually work on the designing part of the database. They keep a close watch on what data should be kept and in what format. They identify and design the whole set of entities, relations, constraints, and views. End Users End users are those who actually reap the benefits of having a DBMS. End users can range from simple viewers who pay attention to the logs or market rates to sophisticated users such as business analysts. Codd's 12 Rules Rule 1: Information Rule The data stored in a database, may it be user data or metadata, must be a value of some table cell. Everything in a database must be stored in a table format. Rule 2: Guaranteed Access Rule Every single data element (value) is guaranteed to be accessible logically with a combination of table-name, primary-key (row value), and attribute-name (column value). No other means, such as pointers, can be used to access data. 29

30 Rule 3: Systematic Treatment of NULL Values The NULL values in a database must be given a systematic and uniform treatment. This is a very important rule because a NULL can be interpreted as one the following data is missing, data is not known, or data is not applicable. Rule 4: Active Online Catalog The structure description of the entire database must be stored in an online catalog, known as data dictionary, which can be accessed by authorized users. Users can use the same query language to access the catalog which they use to access the database itself. Rule 5: Comprehensive Data Sub-Language Rule A database can only be accessed using a language having linear syntax that supports data definition, data manipulation, and transaction management operations. This language can be used directly or by means of some application. If the database allows access to data without any help of this language, then it is considered as a violation. Rule 6: View Updating Rule All the views of a database, which can theoretically be updated, must also be updatable by the system. Rule 7: High-Level Insert, Update, and Delete Rule A database must support high-level insertion, updation, and deletion. This must not be limited to a single row, that is, it must also support union, intersection and minus operations to yield sets of data records. Rule 8: Physical Data Independence The data stored in a database must be independent of the applications that access the database. Any change in the physical structure of a database must not have any impact on how the data is being accessed by external applications. Rule 9: Logical Data Independence The logical data in a database must be independent of its user s view (application). Any change in logical data must not affect the applications using it. For example, if two tables are merged or one is split into two different tables, there should be no impact or change on the user application. This is one of the most difficult rule to apply. 30

31 Rule 10: Integrity Independence A database must be independent of the application that uses it. All its integrity constraints can be independently modified without the need of any change in the application. This rule makes a database independent of the front-end application and its interface. Rule 11: Distribution Independence The end-user must not be able to see that the data is distributed over various locations. Users should always get the impression that the data is located at one site only. This rule has been regarded as the foundation of distributed database systems. Rule 12: Non-Subversion Rule If a system has an interface that provides access to low-level records, then the interface must not be able to subvert the system and bypass security and integrity constraints. DISTRIBUTED DATABASE A distributed database is a database in which storage devices are not all attached to a common processing unit such as the CPU, [1] and which is controlled by a distributeddatabase management system (together sometimes called a distributed database system). It may be stored in multiple computers, located in the same physical location; or may be dispersed over a network of interconnected computers. Unlike parallel systems, in which the processors are tightly coupled and constitute a single database system, a distributed database system consists of loosely coupled sites that share no physical components. 31