1 Overview of Database Management

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1 1 Overview of Database Management 1.1 Data, information and knowledge Data Data is/are the facts of the World. For example, take yourself. You may be 5ft tall, have brown hair and blue eyes. All of this is data. You have brown hair whether this is written down somewhere or not. In many ways, data can be thought of as a description of the World. We can perceive this data with our senses, and then the brain can process this. Human beings have used data as long as weve existed to form knowledge of the world. Until we started using information, all we could use was data directly. If you wanted to know how tall I was, you would have to come and look at me. Our knowledge was limited by our direct experiences Information Information allows us to expand our knowledge beyond the range of our senses. We can capture data in information, then move it about so that other people can access it at different times. Here is a simple analogy for you. If I take a picture of you, the photograph is information. But what you look like is data. I can move the photo of you around, send it to other people via etc. However, Im not actually moving you around or what you look like. Im simply allowing other people who cant directly see you from where they are to know what you look like. If I lose or destroy the photo, this doesnt change how you look. CHARACTERISTICS OF VALUABLE INFORMATION. In order for information to be valuable it must have the following characteristics, as adapted from Ralph M. Stair s book, Principles of Information Systems: Accurate. Accurate information is free from error. Complete. Complete information contains all of the important facts. Economical. Information should be relatively inexpensive to produce. Flexible. Flexible information can be used for a variety of purposes, not just one. Reliable. Reliable information is dependable information. Relevant. Relevant information is important to the decision-maker. Simple. Information should be simple to find and understand. Timely. Timely information is readily available when needed. Verifiable. Verifiable information can be checked to make sure it is accurate In Brief Data: Facts, a description of the World Information: Captured Data and Knowledge Knowledge: Our personal map/model of the World 1.2 Data processing Vs data management Data processing Data processing refers to the process of performing specific operations on a set of data or a database. A database is an organized collection of facts and information, such as records on employees, inventory, customers, and potential customers. As these examples suggest, numerous forms of data processing exist and serve diverse applications in the business setting. Data processing primarily is performed on information systems, a broad concept that encompasses computer systems and related devices. At its core, an information system consists of input, processing, and output. In addition, an information system provides for feedback from output to input. The input mechanism (such as a keyboard, scanner, microphone, or camera) gathers and captures raw data and can be either manual or automated. Processing, which also can be accomplished manually or automatically, involves transforming the data into useful outputs. This can involve making comparisons, taking alternative actions, and storing data for future use. Output typically takes the form of reports and documents that are used by managers. Feedback is utilized to make necessary adjustments to the input and processing stages of the information system. The processing stage is where management typically exerts the greatest control over data. It also is the point at which management can derive the most value from data, assuming that powerful processing tools are available to obtain the intended results. The most frequent processing procedures available to management are basic activities such as segregating numbers into relevant groups, aggregating them, taking ratios, plotting, and making tables. The goal of these processing activities is to turn a vast collection of facts into meaningful nuggets of information that can then be used for informed decision making, corporate strategy, and other managerial functions.

2 1.2.2 Data Management The official definition provided by DAMA International, the professional organization for those in the data management profession, is: Data Resource Management is the development and execution of architectures, policies, practices and procedures that properly manage the full data lifecycle needs of an enterprise. DAMA International This definition is fairly broad and encompasses a number of professions which may not have direct technical contact with lower-level aspects of data management, such as relational database management. Alternatively, the definition provided in the DAMA Data Management Body of Knowledge (DAMA-DMBOK) is: Data management is the development, execution and supervision of plans, policies, programs and practices that control, protect, deliver and enhance the value of data and information assets. The concept of Data Management arose in the 1980s as technology moved from sequential processing (first cards, then tape) to random access processing. Since it was now technically possible to store a single fact in a single place and access that using random access disk, those suggesting that Data Management was more important than Process Management used arguments such as a customer s home address is stored in 75 (or some other large number) places in our computer systems. During this period, random access processing was not competitively fast, so those suggesting Process Management was more important than Data Management used batch processing time as their primary argument. As applications moved more and more into real-time, interactive applications, it became obvious to most practitioners that both management processes were important. If the data was not well defined, the data would be mis-used in applications. If the process wasn t well defined, it was impossible to meet user needs. 1.3 Comparison of Traditional File-Based Approach and Database Approach At the beginning, you should understand the rationale of replacing the traditional file-based system with the database system File-based System File-based systems were an early attempt to computerize the manual filing system. File-based system is a collection of application programs that perform services for the end-users. Each program defines and manages its data. However, five types of problem are occurred in using the file-based approach: Separation and isolation of data When data is isolated in separate files, it is more difficult for us to access data that should be available. The application programmer is required to synchronize the processing of two or more files to ensure the correct data is extracted. Duplication of data When employing the decentralized file-based approach, the uncontrolled duplication of data is occurred. Uncontrolled duplication of data is undesirable because: Duplication is wasteful Duplication can lead to loss of data integrity Data dependence Using file-based system, the physical structure and storage of the data files and records are defined in the application program code. This characteristic is known as program-data dependence. Making changes to an existing structure are rather difficult and will lead to a modification of program. Such maintenance activities are time-consuming and subject to error. Incompatible file formats The structures of the file are dependent on the application programming language. However file structure provided in one programming language such as direct file, indexed-sequential file which is available in COBOL programming, may be different from the structure generated by other programming language such as C. The direct incompatibility makes them difficult to process jointly. Fixed queries / proliferation of application programs File-based systems are very dependent upon the application programmer. Any required queries or reports have to be written by the application programmer. Normally, a fixed format query or report can only be entertained and no facility for ad-hoc queries if offered. File-based systems also give tremendous pressure on data processing staff, with users complaints on programs that are inadequate or inefficient in meeting their demands. Documentation may be limited and maintenance of the system is difficult. Provision for security, integrity and recovery capability is very limited Database Approach In order to overcome the limitations of the file-based approach, the concept of database and the Database Management System (DMS) was emerged in 60s. Advantages A number of advantages of applying database approach in application system are obtained including: Control of data redundancy The database approach attempts to eliminate the redundancy by integrating the file. Although the database approach does not eliminate redundancy entirely, it controls the amount of redundancy inherent in the database.

3 Data consistency By eliminating or controlling redundancy, the database approach reduces the risk of inconsistencies occurring. It ensures all copies of the idea are kept consistent. More information from the same amount of data With the integration of the operated data in the database approach, it may be possible to derive additional information for the same data. Sharing of data Database belongs to the entire organization and can be shared by all authorized users. Improved data integrity Database integrity provides the validity and consistency of stored data. Integrity is usually expressed in terms of constraints, which are consistency rules that the database is not permitted to violate. Improved security Database approach provides a protection of the data from the unauthorized users. It may take the term of user names and passwords to identify user type and their access right in the operation including retrieval, insertion, updating and deletion. Enforcement of standards The integration of the database enforces the necessary standards including data formats, naming conventions, documentation standards, update procedures and access rules. Economy of scale Cost savings can be obtained by combining all organization s operational data into one database with applications to work on one source of data. Balance of conflicting requirements By having a structural design in the database, the conflicts between users or departments can be resolved. Decisions will be based on the base use of resources for the organization as a whole rather that for an individual entity. Improved data accessibility and responsiveness By having an integration in the database approach, data accessing can be crossed departmental boundaries. This feature provides more functionality and better services to the users. Increased productivity The database approach provides all the low-level file-handling routines. The provision of these functions allows the programmer to concentrate more on the specific functionality required by the users. The fourth-generation environment provided by the database can simplify the database application development. Improved maintenance Database approach provides a data independence. As a change of data structure in the database will be affect the application program, it simplifies database application maintenance. Increased concurrency Database can manage concurrent data access effectively. It ensures no interference between users that would not result any loss of information nor loss of integrity. Improved backing and recovery services Modern database management system provides facilities to minimize the amount of processing that can be lost following a failure by using the transaction approach. Disadvantages In split of a large number of advantages can be found in the database approach, it is not without any challenge. The following disadvantages can be found including: Complexity Database management system is an extremely complex piece of software. All parties must be familiar with its functionality and take full advantage of it. Therefore, training for the administrators, designers and users is required. Size The database management system consumes a substantial amount of main memory as well as a large number amount of disk space in order to make it run efficiently. Cost of DBMS A multi-user database management system may be very expensive. Even after the installation, there is a high recurrent annual maintenance cost on the software. Cost of conversion When moving from a file-base system to a database system, the company is required to have additional expenses on hardware acquisition and training cost. Performance As the database approach is to cater for many applications rather than exclusively for a particular one, some applications may not run as fast as before. Higher impact of a failure The database approach increases the vulnerability of the system due to the centralization. As all users and applications reply on the database availability, the failure of any component can bring operations to a halt and affect the services to the customer seriously.

4 1.4 Data Independence The ability to modify a scheme definition in one level without affecting a scheme definition in a higher level is called data independence. There are two kinds: 1. Physical data independence The ability to modify the physical scheme without causing application programs to be rewritten Modifications at this level are usually to improve performance 2. 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. 1.5 Database administration role Page 27 from Korth and sudarsan 1.6 DBMS Users page 26 from Korth and sudarsan 1.7 Data Dictionary Page from Korth and Sudarsan 1.8 Database language Data Definition Language-DDL Data Definition Language (DDL) statements are used to define the database structure or schema. CREATE - to create objects in the database ALTER - alters the structure of the database DROP - delete objects from the database TRUNCATE - remove all records from a table, including all spaces allocated for the records are removed COMMENT - add comments to the data dictionary RENAME - rename an object Data Manipulation Language (DML) Data Manipulation Language (DML) statements are used for managing data within schema objects. SELECT - Retrieve data from the a database INSERT - Insert data into a table UPDATE - Updates existing data within a table DELETE - deletes all records from a table, the space for the records remain MERGE - UPSERT operation (insert or update) CALL - Call a PL/SQL or Java subprogram EXPLAIN PLAN - explain access path to data LOCK TABLE - control concurrency Data Control Language (DCL) Data Control Language (DCL) statements. GRANT - gives user s access privileges to database REVOKE - withdraw access privileges given with the GRANT command

5 1.8.4 Transaction Control Language (TCL) Transaction Control (TCL) statements are used to manage the changes made by DML statements. It allows statements to be grouped together into logical transactions. COMMIT - save work done SAVEPOINT - identify a point in a transaction to which you can later roll back ROLLBACK - restore database to original since the last COMMIT SET TRANSACTION - Change transaction options like isolation level and what rollback segment to use