Section 05 Concepts Of DBMS 1

HSQ - DATABASES & SQL

And Franchise Colleges

05 Concepts of DBMSBy MANSHA NAWAZ

Section 05 Concepts Of DBMS 2

Introduction

• In this lecture we will be looking at some of the fundamental concepts behind a Database Management System (DBMS).

– RDBMS - Relational DBMS

• Exploring the Advantages and Disadvantages of using a DBMS

• Exploring the Architecture of a DBMS and some of the associated issues.

Section 05 Concepts Of DBMS 3

Advantages of the DBMS Approach

• The Database Approach Versus the Traditional File Processing Approach

– Storing data in a non-redundant database improves consistency of data.

• There is only one copy of each item of data.

• Unproductive Maintenance avoided.

– In file based systems, changes to file structure cause endless problems on maintenance (re-writing code).

– Using a DBMS, program access is through a limited view (using SQL).

• Thus programs can’t see minor changes to the database.

• We will be exploring data independence in more detail later .

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Some of the Advantages of using a DBMS

Sharing of data Control of redundancy and thus Data consistency Improved data integrity Better data accessibility Representing complex relationships among data Enforcing integrity constraints Better security of data (as long as backup is perfect) More control over concurrency Better backup and recovery procedures Providing multiple interfaces Faster development of new applications Economy of scale

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Some of the Disadvantages of using a DBMS

High cost of Software Hardware costs high due to software complexity Requirement for skilled staff Higher programming costs - greater skill required Slower processing of some applications Increased vulnerability (all your eggs in one basket) More difficult recovery (if disaster strikes)

Section 05 Concepts Of DBMS 6

DBMS Architecture

• Usually taken to imply a three level architecture.

• The complexity of a large database is handled by a DBMS by providing three views of the data.

– An internal view of how the data is stored and accessed

– A conceptual view of what data is available in the database.

– Local or external views which are a limited and simplified view of the database as suitable for a single application or group of associated applications.

• Data abstraction

– Users deal with conceptual representation of the data.– They have little control over how the data is stored.

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Three Level Architecture

External Level

View 1

View 4

View 2

View 3 et

c.

Conceptual Level Conceptual Schema

Internal SchemaInternal Level

Physical Data Independence

Logical Data Independence

• One of the fundamental aspects of the database approach using a DBMS is that, by providing levels of data abstraction, it hides complexity of data storage from users.

ERD - Logical View

ERD - Table View

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Database schema - the description of a database

• Schema - a description of a database in terms that a DBMS understands

• External Schema

– A database system may have several external schemas each suitable for a

single application or group of associated applications.

– They provide a means of limiting the perceived complexity of a large system.

– Hide those parts of the database which are not required for a particular

purpose or department (useful security).

– External schemas are based on the conceptual schema.

– Each external schema describes a section of the database of interest to a

particular group of users (or programs).

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Client/Server Architecture

User Workstation

User Workstation

OperatorWorkstation

DepartmentFile-Servers

Corporate Servers

• Server provides services for the Clients which are responsible for interacting with the users (Input/Output)

• Server is responsible for performing a service (e.g. transaction) and guaranteeing the integrity of the data

• Well suited for distributed systems handling large amounts of data

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E-R Model NF

Systems Analysis & Design DFD DataStores, DataFlows and Data Dictionary

DBMS

PHYSICAL VIEW OF DATATABLES

LOGICAL VIEW OF DATAFORMS

DATA MODEL

TABLE SET

Database connectivity via websites

www .net technologyMacromedia Dreamweaver

MS Visual Studio

Database connectivity via desktop DBMS such as

MS Access

Database connectivity via programming

languages such as MS Visual Basic

Area of Interest

Database Development

Section 05 Concepts Of DBMS 11

End of Lecture