Database
- 1. THE CONCEPT OF DBMS AND RDBMS Database concept A database is an integrated collection of well defined data and information, centrally controlled in all aspects, created and stored in a typical structure for an organization. In an organization the database could be one or more depending upon the needs and operations of the organization. The data structure and its storage should be such that it facilitates, share ability, availability, resolvability and integrity of the data. The database separates a design of the information system from the data design and its management. Conventionally, in an information system, the information system, the information is obtained by developing the system and integrating them. This calls for breaking the system into various subsystems and developing the information systems independently. In this approach, each system will have its master files and transaction files. They have to be processed separately at different times, depending upon the needs and schedules. The file layouts and the access methods could be different in different systems. Therefore, the files are updated at different times. This approach does affect the quality of the information across all the systems due to various reasons. The data in many systems are common, and there is repetition of data storage in various systems. This is called data redundancy. The redundancy of data current and same in all the files, the management is complex in such a situation. The reports generated out of such files show discrepancies in the information. Since the data files are different for different need to be created at different times. Transaction updating is also carried out at different times. It requires the increase of a magnetic media for storage because the systems are developed independently. The redundancy causes lack of integrity and inconsistency of the data in various files. The following are the main causes which gave birth to database: 1. The data redundancy and inconsistency: since the files are created for each application differently, the files are likely to have different formats and data design as they are created by different designers and programmers over in period of time. Hence, the same data record may be present in more than on file, the creation, updating, and deletion of which is managed by different programmer. Over a period of time, a situation arises when the data is redundant and inconsistent, due to the changes not being incorporated simultaneously in all the applications and in all the files. 2. Difficulty in access to the data: in conventional system design, the file structure is consistent to the specific information needs. If the information needs change, gaining access to the data present in different files to satisfy the revised need, requires writing the necessary application programs every time. This is difficult and very time consuming at critical times. 3. Security problems: the file systems have a limitation of controlling the access to the record causing in security with respect to the information. Since the application programs are written time to time and again, it is difficult to enforce a discipline on the security constraints across all the applications. 4. Integrity of the data: in a file system, it is difficult to maintain integrity of the data across the application. The integrity rules are added when the programs are written. If any changes in the rules occur, it is very difficult to ensure that it is affected across the files in all the applications. 5. To eliminate the above problems, database approach is suggested. The database is designed independent of its use for the application. In other words, the user of the database should view the data in the database as on which he can develop his systems separately. Since, the database matching his needs is common, the problems of redundancy and inconsistency are eliminated. The advantages in the database approach are as follows: • The application system can be developed independent of the database
- 2. • Any report using the information will not be inconsistent • Easy access to the database as per needs • The data validation and updating will be once and same for all • The data is shared by all the users • The data security and privacy can be managed and ensured because data entry in the database occurs once only and is protected by the security measures • Since the database is a storage of the structured i9nformation, the queries can be answered fast by using the logic of the data structures WHAT IS A DATABASE MANAGEMENT SYSTEM (DBMS) The DBMS is software designed to manage and maintain the database of an organization. The main steps are data structuring, defining, integrating, updating and creating. Through these steps, it manipulates the data and provides an environment which is appropriate to use in retrieving and storing the database information. The DBMS is a collection of the interrelated files and a set of programs through which the users can access and modify their files. DBMS is software that facilitates flexible management of data. It is generally composed of three sub- systems which are described as follows: 1. Database definition: in this sub-system, the complete database is described with help of a special language known as the Data Description Language (DDL). However, in the case of database in different files, one file at a time may be defined as that would give maximum flexibility. 2. Database manipulation: after the database is defined, elements of data can be stored. The stored data may either be retrieved or updated later through data manipulation language (DML). The manipulation sub- system can retrieve the required elements of data in a variety of sequences. 3. Database support: this sub-system performs database utility or service functions that include functions like list files, change file passwords, change file capacities, print file statistics, unlock files, etc. In DBMS performs a wide variety of functions, which are discussed as follows: 1. Data organization: DBMS organizes data items as per DDl. Database administrator decides about the data specification that are most suited top each applications. 2. Data integration: data is inter-related together at the element level and can be manipulated in much combination during execution of a particular application program. DBMS facilitates collection, combination, and retrieval of the required data to the user. 3. Physical/logical level separation: DBMS separates the logical description and relationships of data from the way in which the data is physically stored. It also separates out application, programs and their associated data. This adds data insecurity in view of the data access by different programs that describe data in different ways. 4. Data control: DBMS receives requests for storing data from different programs. It controls how and where data is physically stored. Similarly, it locates and returns requested data to the programs. 5. Data protection: data protection and security is one of the major concerns in a database. DBMS protects the data against access by unauthorized users, physical damage, and operating system failure, simultaneous updating, etc. it also protects and secures the content of a database as well as the relationships of data elements. DBMS is equipped with a facility to backup data and restore it automatically in the case of any system failure. Concurrent access control is ensured by the provision of ‘locks’. Other security features implemented in the system include password protection and sophisticated encryption schemes. 6. Data stores: the data are stored in a database in a particular manner. The user of the database needs not to know how the data are actually stored. 7. Data definition and data directory: since the data independence is provided to the user, it requires that all the users understand the data in same manner. Therefore, each data entity is defined in the system and its directory is formed for all the users. 8. Interrogation: in interrogation, the data are selected from the database and extracted or copied for
- 3. processing. For interrogation, it is necessary to identify the data or a part of the data and then through the use of query language the information is processed and printed. 9. Updating: the database needs updating as the value of the data keep changing from time to time. The updates are made by processing the transaction data against the data in the database. 10. Creation: initially, the database is to be created in the manner and the kind as defined in the DBMS. The data is entered in the database by the transaction processing. A special program is written to create the database. The DBMS organizes the data internally in the structure defined in the DBMS. TYPES OF DATABASE STRUCTURE OR DATA MODELS Generally, database system are classified on the basis of one of the three data models, they use in building the conceptual structure or schema of the database. The three models are: 1. Hierarchical model 2. Network model, and 3. Relational model Hierarchical model: in the hierarchical structure, the relationships between records are stored in the form of a hierarchy or a tree which has a root. In this model, all records are dependent and arranged in a multiline structure, thus the root may have a number of branches and each branch may have a number of sub-branches and so on. The lowermost record is known as the ‘child’ of the next higher level record, whereas the higher level record is called the ‘parent’ of its child records. Thus in this approach, all the relationships among records are one-to-many. The hierarchical database model (HDBM) is applicable when the data in an organization can be put down in the hierarchical or in terms of the levels, one after another. The data model is equivalent to the tree. A tree has roots, branches and leaves; their equivalent s in the HDBM beings records, notes and field. In the HDBM the data is stored in the hierarchical form recognizing the fact that each of the levels is bounded by the parent-child relations to the earlier level. The typical characteristics of HDBM are: HDBM starts with a root and has several roots A root will have several branches Each branches is connected to one and only one root A branch has several leaves and a set of leaves are connected to one branch Network database model: the NDBM interconnects the entities of an organization into a network. The NDBM deals with the set of the records components, a part, a subassembly and an assembly are the records. A record located at the tail of the arrow is known as a member record at the head of the arrow is known as an owner. An arrow connecting the owner to a member is a set. Relational Database Model: in the RDBM, the concept of two dimensional tables is used to show the relations. The relational model is currently more popular among users and developers because of the many interrelated tables, the overall design may get complicated which may lead to slower searches and thus affecting the access time. RDBMS Organization needs that MIS would give them a ‘competitive strength’. Simply computerizing the back office or the front office operations is no lo0nger sufficient. The need is to handle an on-line operation, mission, control applications and exercise the operational and management control. The need demands a tool to effectively handle both the transaction processing and the decision processing requirements. It also requires the capability of dealing with hundreds of users who are using, and updating a large database. The need further demands the use of multiple databases residing on the hardware platforms situated at different location-nearby sites and remote site. The decision-making is required more in a real time environment where the decision-making process, right from the problem definition to solution, needs to be handled quickly. The business environment is distributed and
- 4. decentralized requiring a real time resources (hardware, software, data, information) sharing with a complex data flow. All this demands the RDBMS which can serve both the decision support and the transaction processing requirements. The latest RDBMS systems have two sub-systems or parts. One deals with the data management and transaction processing which is independent of its applications in the information processing. The second part provides a set of tools for developing and utilizing on-line application for the decision support. This is handled by the client-server architecture which separates the data management functions from its application. The data management function is handled by the server and the applications are handled by the client. The server centrally enforces all integrity, security and autonomy rules and the client (user) makes use of the database over the network of heterogeneous hardware. The latest trend in the information technology is to make the end user computing simple, easy to understand and easy to use. The concept is extended to the system analyst and programmer, where the RDBMS provides the tools, saving, development and processing time. It allows the business rules of the organization, standard transactions and queries to be programmed once and makes them available to all the users and developers as a stored procedure in the data dictionary. These stored procedures can be nested to develop an application. These procedures are both, reusable and sharable and are developed using the standard SQL. The RDBMS is also capable through the interface to handle the data sources from the other database and application tools developed on different operating systems. The modern RDBMS system operates under the client-server environment as against the traditional master-slave environment. In the traditional DBMS system, a transaction is processed in the database, i.e. the creation, validation and checking the transaction integrity logic. This is done for each transaction separately based on the procedures developed forced transaction for validity and integrity checks. In the modern RDBMS system, the third step of the integrity checking is done through a stored procedure common to all types of transaction. Modern RDBMS allows high level security by providing various tools to the system administrators, the database owners and the users to grant and revoke permission to the specified users or a group of users on the specified tables, view, columns, stored procedures and commands. In the traditional DBMS system, the data was required to store in different databases In line with the security levels. While in the modern RDBMS system a multiple security is taken care of by one integrated DBMS. The latest RDBMS allows an online maintenance, rapid recovery and software based fault tolerance. These features ensure the availability of the database round the clock as the database maintenance is possible online when the system is in use. The maintenance activity consists of the following tasks: 1. Backup 2. Diagnostic 3. Integrity changes 4. Recovery 5. Design changes 6. Performance tuning The rapid recovery feature also the system administrator to provide a ‘time’ to go back for recovery of the data if the system fails due to the power failure or network crash. Based on this, time systems automatically go and collect all the changes and writes the risk. The modern RDBMS, unlike the traditional DBMS, handles the distributed heterogeneous data sources, software environment and hardware platforms. The system is open RDBMS. The modern business activity using the multiple hardware-software platforms, such a business enterprise has multiple databases residing at various locations. The information needs call for the unification and coordination of these databases. The data would get updated in distributed access to the distributed data. RDBMS allows communication at the database level and performs in a unified manner as a single entity through the
- 5. updates, and processing would take place at the respective distributed locations. This is achieved through a software interface across the organization. Since the environment is distributed, it calls for a distributed integrity control and autonomy to perform. The distributed integrity control is achieved through the stored procedures is made to protect the database from a remote external update or processing to maintain the autonomy which would be affected by the unauthorized update from remote locations. The characteristics of modern RDBMS includes hardware independency, software independence, workability under a client-server architecture, a control feature of integrity, security and autonomy and built-in communication facilities to achieve and open the system features for the MIS. It therefore provides a very efficient and effective tool to a skillful designer, developer and user for handling the information needs of the business enterprise.
- 6. updates, and processing would take place at the respective distributed locations. This is achieved through a software interface across the organization. Since the environment is distributed, it calls for a distributed integrity control and autonomy to perform. The distributed integrity control is achieved through the stored procedures is made to protect the database from a remote external update or processing to maintain the autonomy which would be affected by the unauthorized update from remote locations. The characteristics of modern RDBMS includes hardware independency, software independence, workability under a client-server architecture, a control feature of integrity, security and autonomy and built-in communication facilities to achieve and open the system features for the MIS. It therefore provides a very efficient and effective tool to a skillful designer, developer and user for handling the information needs of the business enterprise.