Database System Architecture

The Functional Components of a database system can be divided into 3 units

• Storage Manager

• Query Processor

• Database users and administrators.

Storage Manager

• It is a program module that provides an interface between the database and application program.

• The storage manager is responsible for storing, retrieving and updating the data in the database.

Storage Manager Components• Authorization and Integrity manager

– Which tests for the satisfaction of integrity constraints and checks the authority of users to access data.

• Transaction Manager– Which ensures that the database remains in a

consistent state when the system failures and that concurrent transaction executions proceed without conflicting.

Storage Manager Components

• File Manager– Which manages the allocation of storage

space on disk and data structures used to store those information's

• Buffer Manager– Which is responsible for fetching data from

disk into main memory.

Data Structure used by the storage Manager

• Data Files– Stores database

• Data dictionary– Structure of the database

• Indices– Which can provide fast access to data items.

Hashing technique is used for accessing

Query Processor

• DDL Interpreter– Which interprets DDL statements (Convert

DDL statement into Low level data)

• DML Compiler– Translates MDML statements

• Query Evaluation Engine– Which execute low level instructions

generated by the DML compiler.

Database Users• Application programmers

– Program written in a host language• Sophisticated users

– Interact with the database using query language (analysis)

• Specialized user– Specialized users who write specialized database

applications that do the into the traditional data processing frame work (example CAD system, Knowledge based expert system)

• Naïve users– Interact with the system by invoking one of the

permanent application (tellers agents, web users)

Database Administrator• A Person who has such central control over the

system is called a database administrator (DBA).The functions are

– Schema definition• Set of data definition statements in the DDL.

– Storage structure and access method definition– Schema and physical organization modification.

• Alter the physical organization to improve performance– Granting of authorization for data access (give

authorization)– Routine maintenance

• Periodically backup database• Ensuring that enough free disk space• Monitoring jobs

DBMS

Advantages of DBMS1. Control of data redundancy2. Data Consistency3. Sharing of data4. Improved security5. Enforcement of standards6. Economy of scale7. Balance of conflicting requirements8. Improved data accessibility and responsiveness.9. Increased productivity10. Increased maintenance through data independence.11. Increased concurrency.12. Improved backup and recovery services.

Disadvantages of DBMS• Complexity

• Size

• Cost of DBMS

• Additional hardware cost

• Cost of conversion

• Performance

• Higher impact of failure.