 Introduction Introduction  Purpose of Database SystemsPurpose of Database Systems  Levels of Abstraction Levels of Abstraction  Instances and Schemas Instances and Schemas  Data Independence Data Independence  Database Administrator Database Administrator  Database Users Database Users  Advantages of DBMS Advantages of DBMS

A database is an organized collection of data. The data are typically organized to model relevant aspects of reality in a way that supports processes requiring this information. For example, modelling the availability of rooms in hotels in a way that supports finding a hotel with vacancies. Database management systems (DBMSs) are specially designed applications that interact with the user, other applications, and the database itself to capture and analyze data. A general-purpose database management system (DBMS) is a software system designed to allow the definition, creation, querying, update, and administration of databases

Well-known DBMSs include My SQL, Postgre SQL, SQ Lite, Microsoft SQL Server, Oracle, SAP, dBASE, FoxPro, IBM DB2, Libre Office Base and FileMaker Pro. A database is not generally portable across different DBMS, but different DBMSs can interoperate by using standards such as SQL and ODBC or JDBC to allow a single application to work with more than one database.  Collection of interrelated data  Set of programs to access the data  DMBS contains information about a particular enterprise  DBMS provides an environment that it both convenient and efficient to use Back

Database management systems were developed to handle the following difficulties of typical file-processing systems supported by conventional operating systems:  Data redundancy and inconsistency  Difficulty in accessing data  Data isolation – multiple files and formats  Integrity problems  Atomicity of updates  Concurrent access by multiple users  Security problems Back

 Physical level: Describes how a record (e.g. customer) is stored.  Logical level: Describes data stored in database, and the relationships among the data. type customer = record name: string; street: string; city: integer; end;  View level: Application programs hide details of data types. Views can also hide information (e.g. salary) for security purposes. Back

 Similar to types and variables in programming languages  Schema – the logical structure of the database Example: The database consists of information about a set of customers and accounts and the relationship between them) Analogous to type information of a variable in a program Physical schema: database design at the physical level Logical schema: database design at the logical level

 Instance – the actual content of the database at a particular point in time Analogous to the value of a variable  Physical Data Independence – the ability to modify the physical schema without changing the logical schema Applications depend on the logical schema In general, the interfaces between the various levels and components should be well defined so that changes in some parts do not seriously influence others. Back

 Ability to modify a schema definition in one level without affecting a schema definition in the other levels.  The interfaces between the various levels and components should be well defined so that changes in some parts do not seriously influence others.  Two levels of data independence Logical data independence Physical data independence Back

 Coordinates all the activities of the database system; the database administrator has a good understanding of the enterprise’s information resources and needs  Database administrator’s duties include: Schema definition Storage structure and access method definition Schema and physical organization modification Granting user authority to access the database Back

Users are differentiated by the way they expect to interact with the system.  Application programmers: Interact with system through DML calls.  Specialized users: Write specialized database applications that do not fit into the traditional data processing framework  Sophisticated users: Form requests in a database query language.  Naive users: Invoke one of the permanent application programs that have been written previously Back

 Controlling Data Redundancy In non-database systems each application program has its own private files. In this case, the duplicated copies of the same data is created in many places. In DBMS, all data of an organization is integrated into a singledatabase file.  Sharing of Data In DBMS, data can be shared by authorized users of the organization. The database administrator manages the data and gives rights to users to access the data. Many users can be authorized to access the same piece of information simultaneously.

 Report Writers Most of the DBMSs provide the report writer tools used to create reports. The users can create very easily and quickly. Once a report is created, it can be used may times and it can be modified very easily.  Control Over Concurrency In a computer file-based system, if two users are allowed to access data simultaneously, it is possible that they will interfere with each other. For example, if both users attempt to perform update operation on the same record, then one may overwrite the values recorded by the other.

 Integration of Data In Database management system, data in database is stored in tables. A single database contains multiple tables and relationships can be created between tables (or associated data entities). This makes easy to retrieve and update data.  Integration Constraints Integrity constraints or consistency rules can be applied to database so that the correct data can be entered into database. The constraints may be applied to data item within a single record or the may be applied to relationships between records.

 Data Security Form is very important object of DBMS. You can create forms very easily and quickly in DBMS. Once a form is created, it can be used many times and it can be modified very easily. The created forms are also saved along with database and behave like a software component.  Data Consistency By controlling the data redundancy, the data consistency is obtained. If a data item appears only once, any update to its value has to be performed only once and the updated value is immediately available to all users. If the DBMS has controlled redundancy, the database system enforces consistency. Back

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