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Chapter 1

Database ConceptsDatabase Concepts

Chapter 1 &2 in Textbook

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Database ConceptsDatabase ConceptsData is a meaningless static value. What does 3421 means?

Information is the data you process in a manner that makes it meaningful. Information can be provided only if proper data exists.

A database (DB) is a collection of related persistent data. Can be generated & maintained manually or automatically

Data is what you store in database. Information is what you retrieve from a database.

A database application is a collection of data and the programs that allow the manipulation of these data to meet the information needs of an enterprise

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Database Application: ExamplesDatabase Application: Examples

• The e-shop around the corner

• KSU Library

• Saudia Airline Reservations

• KSU University

 

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Database ConceptsDatabase Concepts

A database application is usually implemented using a Database Management System (DBMS)

Database System (DBS) is DB + Software (DBMS + Application program) (TO BE CONTINUED ..)

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DBS EnvironmentDBS Environment

DatabaseMeta-Data

Data Access

Query Process

Application Programs

DBMS

DBS

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File-Based Systems (FBS)File-Based Systems (FBS)

FBS is a collection of application programs that perform tasks where each program defines and manages its own data.

DataEntry

Filehandling

File DefUser 1

Application Program 1 File1

DataEntry

Filehandling

File DefUser 2

Application Program 2 File 2

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File-Based Systems (FBS)File-Based Systems (FBS)Major Disadvantages of FBS:

• Data Redundancy & Inconsistency• Data Isolation• Data Dependence• Incompatible File Format• Fixed Queries/Proliferation of application

programs

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File-Based Systems (FBS)File-Based Systems (FBS)

The limitations of the FBS approach attributed to two factors:

• The definition of data is embedded in the application programs

• There is no control over the access & manipulation of data beyond the imposed by the application program

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DataBased Systems (DBS)DataBased Systems (DBS)

DBS is a single large repository of data, defined once & used by many application programs.

User 1

Application Program 1

DatabaseUser 2

Application Program 2

DataEntry

DataEntry

DBMS

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Database Systems (DBS) Database Systems (DBS) Ref 1Ref 1

Major Characteristics of DBS:

• Self-Describing nature • Program-Data Independence• Sharing of Data & Multi-user Transactions

(Concurrency Control)• Support of Multiple Views of the Data

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Database Systems (DBS)Database Systems (DBS)

Staff_No FName LName Age Salary Bno

Staff_No FName LName Age Salary Staff_No LName Bno

View 1 View 2

DBS Support of Multiple Views of Data

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Database Systems (DBS)Database Systems (DBS)

Disadvantages of DBS:

• Complexity• Size• Cost (DBMS,Hardware, Staff, Training)• Performance• Higher impact of a failure

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Database Management SystemDatabase Management System(DBMS)(DBMS)

A DBMS is a collection of software that facilitates the implementation and management of database applications

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Database Management System Database Management System (DBMS)(DBMS)

DBMS facilitates the following:

• Creating and Defining a DB• Construct and Store a DB• Manipulate a DB (query & update the DB)• Control access to data

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Database Management SystemDatabase Management System

Major Relational DBMS vendors/products

• Paradox by Corel• dBase, Clipper• FoxPro, Access & SQL Server by MS • MySQL• DB2 by IBM • Oracle, Sybase, Informix

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DBS EnvironmentDBS Environment

DBMSApp

Program

DB

UserRequirement

Procedure

DBA

Naïve End User

Applicationprogrammer

DB Designer System Analyst

Sophisticated End User H/W

Design

Communicate

Manage

Write Write

Program

Use

Use

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Database PeopleDatabase People• Database Administrator (DBA): administrates the DB, DBMS & related

software

• Database Designer: Identify the data & choose the appropriate structure to represent &store the data

• Database user: Queries/modifies data- Naïve users: invoke one of the permanent application programs that have been written previously

- Sophisticated users: form requests in a database query language

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Database PeopleDatabase People

• System Analyst: determine the requirements of end users & develop system specifications

• Application Programmer: implement system specifications

• DBMS designer & Implementers

• Tool Developer

• Operators & Maintenance Personnel

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Three-Schema Architecture

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Three-Schema Architecture

Database

InternalDescription

ConceptualDescription

View 2 View nView 1

User 1 User 2 User n

ExternalLevel

ConceptualLevel

InternalLevel

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Three-Schema Architecture

•Internal level: describes how data is stored. The way perceived by the DBMS & OS.

•Conceptual level: describes what data stored in DB, and the relationships among the data. The way perceived by the DBA & programmers.

•External level: describes the part of the DB that user is interested in. The way perceived by the end users.

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Three-Schema Architecture

Emp_No FName LName Dept_No Emp_No LName Salary

View 1 View 2

InternalLevel

ConceptualLevel

EMPLOYEEEmp_No CHAR(6)FName CHAR(15)LName CHAR(15)Dept_No CHAR(3)Salary NUMBER(5)

PREFIX TYPE=BYTE(6),OFFSET=0EMP# TYPE=BYTE(6),OFFSET=6, INDEX=EMPXLNM TYPE=BYTE(15),OFFSET=12FNM TYPE=BYTE(15),OFFSET=27DPT# TYPE=BYTE(4),OFFSET=42PAY TYPE=FULLWORD,OFFSET=46

ExternalLevel

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Schemas & Instances

Schema is the description of the DB.It rarely changes.

Instance is the actual content of the DB at a particular point in time. Data is actual "instance" of DB, changes rapidly.

The concepts of Schema & Instances corresponds to Types & Values in programming languages, respectively

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Mapping

Mapping is the process of transforming requests and results between the Internal, Conceptual & External levels.

Two types of mapping:

- External / Conceptual mapping

-Conceptual / Internal mapping

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Data Independence

Data Independence is the ability to modify a schema definition in one level without affecting a schema definition in the next higher level.

Two levels of data independence:

– Logical data independence

– Physical data independence

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Data Independence

InternalSchema

ConceptualSchema

ExternalSchema

ExternalSchema

ExternalSchema

External/ConceptualMapping

Conceptual/InternalMapping

Logical data Independence

Physical data Independence

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Data Definition Language (DDL)

DDL is a descriptive language for defining the database schema

DDL compiler generates meta-data stored in a the data dictionary

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Data Manipulation Language (DML)

Two classes of languages

– Procedural: user specifies what data is required and how to get those data

– Nonprocedural: user specifies what data is required without specifying how to get those data (e.g. SQL)

DML is a language for retrieving and updating (insert, delete, & modify) the data in the DB

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Database Languages

DBMS have a facility for embedding DDL & DML (sub-languages) in a High-Level Language (COBOL,PASCAL, C), which in this case is considered a host language.

DBMSCall to DB

C,C++,Lisp,..

Local Vars(memory)

ApplicationProgram

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Data Models

Data Model is a set of concepts for describing the structure of a DB

Categories of data models:

- Object-based conceptual model

- Record-based logical model

- Physical model

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Data Models

Conceptual model is the construction of an enterprise’s information that is independent of implementation details.

Logical model is the logical description of an enterprise’s information with high level description of the implementation.

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Data Models

Physical model

Logicalmodel

Conceptualmodel

Hardware dependentSoftware dependent

Hardware independentSoftware dependent

Hardware independentSoftware independent

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Data ModelsObject-based conceptual model

– Entity-Relationship

– Object-Oriented

– Semantic

– Functional

- Binary

Record-based logical models

– Relational model

– Network model

– Hierarchical model

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Data Models

Staff_No LName Salary Brn_No Brn_No Street Tel_No

St1 Name1 7000 1St2 Name2 4000 1St3 Name3 6500 2St4 Name4 3000 3

1 Olayaa 46300002 Malaz 47800003 Rawda 2310000

St1 Name1 7000 Olayaa 4630000

St2 Name2 4000

St3 Name3 6500

St4 Name4 3000

Malaz 4780000

Rawda 2310000

RelationalModel

NetworkModel

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Data Models

St3 Name3 6500

HierarchicalModel

St1 Name1 7000 St2 Name2 4000

St4 Name4 3000

Olayaa 4630000Malaz 4780000 Rawda 2310000

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Summary of DB Concepts (1)

• Database (DB)

• Database Application

• Database Management System (DBMS)

• Database System (DBS) - Centralized approach

• File-Based System(FBS) - Decentralized approach

• Program-data dependence & independence

• Meta-data & data dictionary

• Concurrency Control

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Summary of DB Concepts (2)• Three-schema Architecture (internal, conceptual, & external levels)

• Schemas &Instances

• Mapping (external/conceptual, conceptual/internal)

• Data Independence (logical & physical)

• Data Definition Language (DDL)

• Data Manipulation Language (DML)

• Query language& host language

• Conceptual model,Logical model,&Physical model

• Data model (Entity-Relationship, Object-Oriented, Relational)