Introduction to Dbms

Contents Introduction Purpose of Database SystemsLevels of Abstraction Instances and SchemasData IndependenceDatabase AdministratorDatabase UsersAdvantages of DBMS

Introduction 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

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Purpose of Database Systems

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

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Levels of Abstraction 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

Instances and Schemas

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 schemaApplications depend on the logical

schemaIn 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

Data IndependenceAbility 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 independenceLogical data independencePhysical data independence

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Database Administrator 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 definitionStorage structure and access method

definitionSchema and physical organization

modificationGranting user authority to access the

database

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Database Users 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.

Advantages of DBMS

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.

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Thank you