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Introduction to Database Systems

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Database and Database System

A database is a shared collection of logically related data designed to meet the information needs of an organization.

Components of a Database SystemsDatabaseHardwareSoftware - DBMSUsers

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Database

The data in the database will be expected to be both integrated and shared particularly on multi-user systems

Integration - The database may be thought of as a unification of several otherwise distinct files, with any redundancy among these files eliminated

Shared - individual pieces of data in the database may be shared among several different users

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Hardware

These are secondary storage on which the database physically resides, together with the associated I/O devices, device controllers etc.

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DBMS

Examples of DBMS Products Oracle Informix Access DB2 Fox pro dBase SQL Server My SQL

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Typical Function of DBMS

• Data storage, retrieval and update• A user-accessible catalog• Transaction support• Concurrency and control services• Recovery services• Authorization services• Support of data communication • Integrity Services• Services to promote data independence• Utility services

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Users

Application Programmer - writes programs that use the database

Database Designers - designs conceptual and logical database

Database Administrator (DBA)Data AdministratorEnd - user - interacts with the

system from an on-line terminal by using Query Languages etc.

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Data & Database Administration

Data Administrator – a business manager responsible for controlling the overall corporate data resources

Database Administrator (DBA) - a technical person responsible for development of the total system

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Sample Applications

Student Records Banking Insurance Billing Systems e.g. Electricity, Phone ISPs Personnel Records Accounting Systems Reservation Systems e.g. Airline, Hotel Medical Records

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Advantages Control of data

redundancy Data consistency Multipurpose use of

data Sharing of data, Enforcement of

standards Economy of scale Balance conflicting

user requirement

Improved data accessibility and responsiveness

Increased productivity Improved maintenance

through data independence

Increased concurrency Improved backup and

recovery services.

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Disadvantages

Complexity Size Cost of DBMS Additional hardware costs Cost of conversion

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Database Architecture

External Level – concerned with the way users perceive the database

Conceptual Level – concerned with abstract representation of the database in its entirety

Internal Level – concerned with the way data is actually stored

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Architecture of Db System

DBMS

Application 2Application 1 Application 3

Database

Conceptual Level

Internal Level

External Level

Logical Data Independence

Physical Data Independence

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Data Independence

Logical Data Independence – users and user programs are independent of logical structure of the database

Physical Data Independence – the separation of structural information about the data from the programs that manipulate and use the data i.e. the immunity of application programs to changes in the storage structure and access strategy

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Data Independence

Different applications will need different views of the same data, so that if they are not interested in a part of the database, that part need not be included in their view. This feature is also important for controlling access to parts of database

The DBA must have the freedom to change the storage structure or access strategy in response to changing requirements, without having to modify the existing applications

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Db Development Life Cycle

Database planning System definition Requirement collection and analysis Database design DBMS selection Application design Prototyping Implementation Data conversion and loading Testing Operational maintenance

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Database Design

Conceptual database design - the process of constructing a model of the information used in an organization, independent of all physical considerations

Step 1 Build local conceptual data model for each user view

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Database Design

Logical database design for the relational model - the process of constructing a model of the info used in an organization based on a specific data model, but independent of a particular DBMS and other physical considerationsStep 2 Build and validate local data model for each user viewStep 3 Build and validate global logical data model

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Database Design

• Physical database design for relational databases - the process of producing a description of the implementation of the database on secondary storage.

Step 4 Translate global data model for target DBMS

Step 5 Design physical representationStep 6 Design security mechanismsStep 7 Monitor and tune the operational

system

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Conceptual Database DesignStep 1 Build local conceptual data model

for each user view Identify entity types Identify relationship types Identify and associate attributes with entity or

relationship Determine attributes domains Determine candidate and primary key attributes Specialize/generalize entity types (optional

step) Draw Entity-Relationship diagram Review local conceptual data model with user

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Logical Database Design for the Relational ModelStep 2 Build and validate local data model

for each user view Map local conceptual data model to local

logical data model Derive relations from local logical data

model Validate model using normalization Validate model against user transactions Draw Entity-Relationship diagram Define integrity constraints Review local logical data model with user

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Logical Database Design for the Relational ModelStep 3 Build and validate global logical

data model Merge local logical data models into

global model Validate global data model Check for future growth Draw final Entity-Relationship diagram Review global logical data model with

users

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Physical Database Design for Relational DatabasesStep 4 Translate global data model for target

DBMS Design base relations Design enterprise constraints for target DBMS

Step 5 Design physical representation Analyze transactions Choose file organizations Choose secondary indexes Consider the introduction of controlled redundancy Estimate disk space requirements

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Physical Database Design for Relational DatabasesStep 6 Design security mechanisms Design user views Design access rules

Step 7 Monitor and tune the operational system