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 DML Compiler Query Evaluation Engine 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 Sophisticated users 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 DBMS Control of data redundancy Data Consistency Sharing of data Improved security Enforcement of standards Economy of scale Balance of conflicting requirements Improved data accessibility and responsiveness. Increased productivity Increased maintenance through data independence. Increased concurrency. Improved backup and recovery services.

Disadvantages of DBMS Complexity Size Cost of DBMS Additional hardware cost Cost of conversion Performance Higher impact of failure.