What is a Database?
Database Management System (DBMS) A database management system (DBMS) is a software package designed to define, manipulate, retrieve and manage data in a database. A DBMS generally manipulates the data itself, the data format, field names, record structure and file structure. It also defines rules to validate and manipulate this data. A DBMS relieves users of framing programs for data maintenance. Query languages, such as SQL, are used along with the DBMS package to interact with a database.A database is the back-end of an application. A DBMS receives instruction from a database administrator (DBA) and accordingly instructs the system to make the necessary changes. These commands can be to load, retrieve or modify existing data from the system. A DBMS always provides data independence. Any change in storage mechanism and formats are performed without modifying the entire applicationWhat is a Database?To find out what database is, we have to start from data, which is the basic building block of any DBMS.Data: Facts, figures, statistics etc. having no particular meaning (e.g. 1, ABC, 19 etc).Record: Collection of related data items, e.g. in the above example the three data items had no meaning. But if we organize them in the following way, then they collectively represent meaningful information.RollNameAge1ABC19?Table or Relation: Collection of related records.RollNameAge1ABC192DEF223XYZ28?The columns of this relation are called Fields, Attributes or Domains. The rows are called Tuples or Records.Database: Collection of related relations. Consider the following collection of tables:T1RollNameAge1ABC192DEF223XYZ28?T2RollAddress1KOL2DEL 3MUM?T3RollYear1I2II3IT4YearHostelIH1IIH2?We now have a collection of 4 tables. They can be called a “related collection” because we can clearly find out that there are some common attributes existing in a selected pair of tables. Because of these common attributes we may combine the data of two or more tables together to find out the complete details of a student. Questions like “Which hostel does the youngest student live in?” can be answered now, although Age and Hostel attributes are in different tables.In a database, data is organized strictly in row and column format. The rows are called Tuple or Record. The data items within one row may belong to different data types. On the other hand, the columns are often called Domain or Attribute. All the data items within a single attribute are of the same data type.?What is Management System?A management system is a set of rules and procedures which help us to create organize and manipulate the database. It also helps us to add, modify delete data items in the database. The management system can be either manual or computerized.The management system is important because without the existence of some kind of rules and regulations it is not possible to maintain the database. We have to select the particular attributes which should be included in a particular table; the common attributes to create relationship between two tables; if a new record has to be inserted or deleted then which tables should have to be handled etc. These issues must be resolved by having some kind of rules to follow in order to maintain the integrity of the database.Database System Environment The term database system refers to an organization of components that define and regulate the collection, storage, management, and use of data within a database environment. These are: ? Hardware ? Software ? People ? Procedures ? Data Hardware It identifies all the system’s physical devices. The database system’s main and most easily identified hardware component is the computer, which might be a microprocessor, a minicomputer, or a mainframe computer. It also include peripherals like keyboard, mouse, modems, printers, etc. Software: refers to the collection of programs used by the computers within the database system. Operating system Software- manages all hardware components and makes it possible for all other software to run on the computers. DOS,OS/2, and Windows used by micro computers. UNIX and used by mini computersDBMS Software- manages the database within the database system. MS-Access, MSSQL Server, Oracle, DB2 etc. are some famous DBMS software. Application Programs & Utilities Software- are used to access and manipulate the data in the DBMS to manage the computer environment in which data access and manipulation take place. System Administrator: oversee the database system’s general operations. Database Administrator: manage the DBMS’s use and ensure that the database is functioning properly. Database Designers: design the database structure. They are in effect the database architects. If the database design is poor, even the best application programmers and the most dedicated DBAs will fail to produce a useful database environment. People System Analysts and Programmers: design and implement the application programs. They design and create the data entry screens, reports, and procedures through which end user access and manipulate the database’s data. ? End Users: are the people who use the application programs to run the organization’s daily operations. E.g. sales clerks, supervisors, managers, and directors are all classified as end users. High-level end users employ the information obtained from the database to make tactical and strategic business decisions. Procedures Procedures are the instructions and rules that govern the design and use of the database system. Procedure are a critical, although occasionally forgotten, component of the system. Procedures play a very important role in a company, because they enforce the standards by which business is conducted within the organization and with customers. These also are used to ensure that there is an organized way to monitor and audit both the data and information. Data The word “data” covers the collection of facts stored in the database. Because data are the raw material from which information is generated, the determination of which data are to be entered into the database and how such data are to be organized is a vital part of the database designer’s job. DBMS Functions A DBMS performs several important functions that guarantee the integrity and consistency of the data in the database. Most of these functions are transparent to end users, and most can be achieved only through the use of a DBMS. Data dictionary management: The DBMS requires that definitions of the data elements and their relationships(metadata) be stored in a data dictionary. In turn, all programs that access the data in the database work through the DBMS. The DBMS uses the data dictionary to look up the required data component structures and relationships, thus relieving us from having to code such complex relationships in each program. Data Storage Management: The DBMS creates the complex structures required for data storage, thus relieving us from the difficult task of defining and programming the physical data characteristics. A modern DBMS system provides storage not only for the data, but also for the related data entry forms or screen definitions, report definitions, data validation rules, procedural code, structures to handle video and picture formats, and so on. Data transformation and presentation: the DBMS transforms entered data to conform to the data structures that are required to store data. Therefore, the DBMS relieves us of the chore of making a distinction between the data logical format and the data physical format. By maintaining the data independence, the DBMS translates logical requests into commands that physically locate and retrieve the requested data. That is, the DBMS formats the physically retrieved data to make it confirm to the user’s logical expectations. Security Management: The DBMS creates a security system that enforces user security and data privacy within the database. Security rules determines which user can access the database, which data items each user may access, and which data operations the user may perform. This is especially important in multi user database systems where many users can access the database simultaneously. Multi user access control: The DBMS creates the complex structures that allow multi user access to the data. In order to provide data integrity and data consistency, the DBMS uses sophisticated algorithms to ensure that multiple users can access the database concurrently without compromising the integrity of the database. Backup and recovery management: The DBMS provides backup and data recovery procedures to ensure data safety and integrity. Current DBMS system provide special utilities that allow the DBA to perform routine and special backup and restore procedures. Recovery management deals with the recovery of the database after a failure, such as a bad sector in the disk or a power failure. Such capability is critical to the preservation of the database’s integrity. Data Integrity Management: The DBMS promotes and enforces integrity rules to eliminate data integrity problems, thus minimizing the data duplicity and maximizing data consistency. The data relationships stored in the data dictionary are used to enforce data integrity. Ensuring data integrity is especially important in transaction-oriented database systems. Database access languages and application programming interface: The DBMS provides data access via a query language. A query language is a nonprocedural language – that is, one that lets the user specify what must be done without having to specify how it is to be done. The DBMS query language contains two components: a DDL and DML. The DBMS also provides data access to programmers via procedural languages.It also provides administrative utilities used by the DBA and the database designer to create, implement, monitor, and maintain the database. Database communication interfaces: Current-generation DBMSs provide special communications routines designed to allow the database to accept end user requests within a computer network environment. In fact, database communications capabilities are an essential feature of the modern DBMS. E.g. the DBMS might provide communications functions to access the database through the Internet, using Internet browsers such as Netscape or Explorer as the front end. ................
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