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Database Management Systems

(DBMS)

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Database Management Systems (DBMS)

Overview of:

Database Management Components

Database Systems Architecture (DSA)

DBMS Functions The Database Approach

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Database Management Overview

A database system is comprised of four major components:

Data, Hardware, Software and Users. Data in a database is both:

Integrated– The database is a unification of several files,

with redundancy eliminated. Shared

– Individual pieces of data can be shared amongst different users. Different users can access the data at the same time (concurrent access).

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Main Advantages of a DBMS

scalability – Expanded, Modified or downsized

Support for client/server systems

Economy of Scale- better utilization of hardware.

Sharing of data

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Main Advantages of a DBMS Balancing Conflicting

requirements.-typically a DBMS is managed by a person called a database administrator(DBA)

Controlled Redundancy Security-The DBA can define

authorization procedures to ensure only legitimate users can access the database.

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DBMS

DBMS require more expensive Hardware Software Data networks capable of

supporting a multi-user environment

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DBMS

DBMS is more complex than a file processing system. Learning curve for systems

analysts, database administrators and users is usually steeper

This increase total cost of ownership (TCO)

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DBMS Components

Provides an interface between a database and the users

Data manipulation language a schema and a physical data repository

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DATABASE

Data manipulation language

Schema and subschema's

Physical data repository

Users

Database

Administrators

Related

Information

Systems

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Users

Users. Users typically work with predefined queries, forms, reports and switchboards, but can also use query languages to access stored data.

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Data Manipulation Language

Controls database operations Storing Retrieving Updating Deleting data

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Data Manipulation Language

Commercial DBMS Oracle and IBM’S DB/2

Use a DML

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Schema

The complete definition of a database including descriptions of all fields, records and relationships.

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Database System Architecture

Three Levels of the ANSI/SPARC architecture:

Internal (Physical) Low level representation of the database,

i.e. indexes. External (User Logical)

The individual user level Conceptual (Community logical)

A view of the total database contents, definitions, security, integrity constraints

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DBMS

The DBMS handles all access to the database. User issues an access request. DBMS intercepts request and

analyses it. DBMS inspects, the external schema

for the user, the conceptual scheme and storage structure definition.

DBMS executes the operations on the stored database.

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DBMS Functions:

Data Definition (DDL compiler or processor) Data Manipulation (DML compiler or

processor) Optimisation and Execution (run-time

manager) Data Security and Integrity Data Recovery and Concurrency (transaction

manager) Data Dictionary (metadata) Performance

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Client/Server Architecture

In this context the DBMS is the server as it supports all the basic functions, data definition, data manipulation, data security and integrity.

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Client/Server Architecture

Clients: the applications that run on top of the DBMS.

Applications

DBMS

End users

Clients

Server

Database

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Distributed Database System

When a system provides total transparency, i.e. each client behaves as if it was dealing with a single server on a single machine = distributed database system.

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The Database Approach:Advantages

Centralised Control Standardisation Balancing Visibility Integrated Processing Controlled redundancy of data Data independence

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The Database Approach:Disadvantages

Cost of Initial Conversion Purchase Installation Training New applications Data entry

Operating Costs – DBMS are resource hungry.

Success – performance degradation Politics (naming conventions)