Lecture1mgaya

8/2/2019 Lecture1mgaya

1/43

Silberschatz, Korth and Sudarshan1.1Database System Concepts

1

RCS 201:

Database Design3 unit courseLecturer Mr Mgaya Gervas B

RUAHACOLLEGE

UNIVERSITY


2/43

RCS 201 Database Design 2

OBJECTIVES OF THE COURSE

To provide students with an awareness of the need for adatabase system, its role in an organization and thestandard database management system (DBMS)architecture.

To provide students with skills to analyse databaserequirement and design well-structured relational databasedesigns


3/43


LEANING OUTCOMES

At the end of this course you should be able to:

1. Explain what is a database

2. Discuss the advantage and disadvantages of database

and explain the architecture of databases

3. Describe the different approaches to database designand list down the advantages of the relational modeldesign

4. Perform INF,2NF, and BCNF normalization, ER andEER modelling

5. Design and implement well-structured relationaldatabase


4/43


Assessment modality

The course will be assessed as follows:

Lectures and practicals attendance: 10marks

Two individual timed tests @ 15 marks= 30

Total coursework 40%

NOTE: THERE WILL BE NO MAKE UP WHAT SO EVER!

WORK HARD!


5/43


TEXTBOOKS1. Elmasri,Ramez & Shamkant Fundamental of

Database Systems

2. Date, C.J Introduction to Database Systems

REFERENCE BOOKS1.SilberschatzKorthSudarshan Database

System Concepts, Fourth Edition


6/43


6

Plan for Intro to DB Systems I

What is:

A database

Data A database management system (DBMS)

Reading:

Chapter 1 of the textbook


7/43Silberschatz, Korth and Sudarshan1.7Database System Concepts

7

Definition of Data (Datum)

Data is a value of a property of an individual UoD object or arelationship (between two UoD objects) at a particular period oftime

Example

UoD object(s) James James & CompSci

Property Age Number of Points

Time Feb 2007 Feb 2007

Value 21 240



8

Definition of a Database

A database is a collection of related data

Essential database characteristics are:

-Represents an aspect of the real world (miniworld,Universe of

Discourse (UoD)), Well structured (even has a strict regular structure),

Reflects (or should reflect) current state of the UoD,

Has users and applications, and

Stored in a permanent (persistent) computer memory

Managed by a Database Management System (DBMS)

All these characteristics have to be met



9

What Is a Database?

RealWorld

facts about the world in a database














more facts

more facts

more facts

more facts

more facts

more facts

more facts

more facts

more facts

more facts

some more rather long facts about the world in the databse












Database

Facts about world and behaviour of world

represented incontents and operations of a database

Users



10

A Sample Database

Studen

t

LName FName StudId Major

Smith Susan 131313 Comp

Bond James 007007 Math

Smith Susan 555555 CompCourse

CName CourId Hours Dept

DB Sys C302 2+1 Comp

SofEng C301 2+0 Comp

DisMat M214 4+1 Math

Grade

StudId CourId Grade

007007 C302 A+

007007 C301 A

007007 M214 A+

131313 C301 B-

555555 C301 C

131313 C302 D

555555 C302 E



11

Database Application Areas

Database Applications: Banking: all transactions

Airlines: reservations, schedules

Universities: registration, grades

Sales: customers, products, purchases

Manufacturing: production, inventory, orders, supply chain

Human resources: employee records, salaries, tax deductions

Databases touch all aspects of our lives



12

Database Management System (DBMS)

A database management system (DBMS) is a

collection of programs that enables users to createand maintain a database.

The DBMS is hence a general-purpose softwaresystem that facilitates the processes of defining,

constructing, and manipulating databases forvarious applications.

Defining a database involves specifying the datatypes, structures, and constraints for the data to be

stored in the database.

Constructing the database is the process ofstoring the data itself on some storage medium thatis controlled by the DBMS.

Manipulating a database includes such functions



13

Database Management System (DBMS)

In a nutshell,

A collection of programs that enable:

Defining (describing the structure),

Populating by data (Constructing),

Manipulating (querying, updating), Preserving consistency,

Protecting from misuse,

Recovering from failure, and

Concurrent using

of a database.



14

A Simplified Database System Layout

Application Programs/Interactive Queries

Catalog Database

Query ProcessorData

Access

DBMS

DatabaseSystem

Users/Programmers

DatabaseDescription

DDL

Compiler

DBA



15

Database system=database +DBMS

Why do We Use a DBMS?

Suppose we need to build a universityinformation system. How do we

Store the data? (use file structure..) Query the data? (write a programme..) Update the data safely?(write more programmes..) Provide different views on the same data? Deal with crashes?



16

Purpose of Database System

In the early days, database applications were built on top of filesystems

Drawbacks of using file systems to store data:

Data redundancy and inconsistency

Multiple file formats, duplication of information in different files

Difficulty in accessing data

Need to write a new program to carry out each new task

Data isolation multiple files and formats

Integrity problems

Integrity constraints (e.g. account balance > 0) become partof program code

Hard to add new constraints or change existing ones



17

Purpose of Database Systems (Cont.)

Drawbacks of using file systems (cont.)

Atomicity of updates

Failures may leave database in an inconsistent state with partialupdates carried out

E.g. transfer of funds from one account to another should eithercomplete or not happen at all

Concurrent access by multiple users

Concurrent accessed needed for performance

Uncontrolled concurrent accesses can lead to inconsistencies

E.g. two people reading a balance and updating it at the same

time Security problems

Database systems offer solutions to all the above problems



18

When Not to Use a DBMS

In spite of the advantages of using a DBMS, there are a few

situations in which such a system may involve unnecessaryoverhead costs as that would not be incurred in traditional fileprocessing. The overhead costs of using a DBMS are due to thefollowing:

High initial investment in hardware, software, and

training. Generality that a DBMS provides for defining and

processing data.

Overhead for providing security, concurrency control,recovery, and integrity functions.



19

3 Levels of Abstraction

1.Physical level describes how a record (e.g., customer) is stored.

2.Logical level: describes data stored in database, and therelationships among the data.

type customer = recordname: string;street: string;city: integer;

end;

3. View level: application programs hide details of data types.Views can also hide information (e.g., salary) for security

purposes.



20

View of Data

An architecture for a database system



21

Instances and Schemas

Similar to types and variables in programming languages

Schema the logical structure of the database e.g., the database consists of information about a set of customers and

accounts and the relationship between them)

Analogous to type information of a variable in a program

Physical schema: database design at the physical level

Logical schema: database design at the logical level

Instance the actual content of the database at a particular point in time

Analogous to the value of a variable

Physical Data Independence the ability to modify the physical schemawithout changing the logical schema

Applications depend on the logical schema

In general, the interfaces between the various levels and components should bewell defined so that changes in some parts do not seriously influence others.



Semantic data models attempt to capture the

meaning of a database. Practically, they provide anapproach for conceptual data modeling.

Over the years there have been several differentsemantic data models that have been proposed.

By far the most common is the entity-relationshipdata model, most often referred to as simply the E-Rdata model.

The E-R model is often used as a form ofcommunication between database designers and theend users during the developmental stages of adatabase.

Introduction to Data Modeling



23

Data Models

Data models is a collection of tools for describing data

data relationships

data semantics

data constraints

Entity-Relationship model Conceptual model to identify data & important relationships

Relational model

mathematical model based on set-theory

Most commercial DBMSs are based on it Other models:

Object-oriented model, Object-relational model

semi-structured data models Older models: network model and hierarchical model


24/43


24

Entity-Relationship Model

Example of schema in the entity-relationship model


25/43


25

Entity Relationship Model (Cont.)

E-R model of real world

Entities (objects)

E.g. customers, accounts, bank branch

Relationships between entities

E.g. Account A-101 is held by customer Johnson

Relationship set depositorassociates customers with accounts Widely used for database design

Produces specification of the data and relationship to maintain in thedatabase.

Database design in E-R model usually converted to design in the

relational model (coming up next) which is used for storage andprocessing


26/43


26

Relational Model

Example of tabular data in the relational model

customer-name

Customer-idcustomer-street

customer-city

account-number

Johnson

Smith

Johnson

Jones

Smith

192-83-7465

019-28-3746

192-83-7465

321-12-3123

019-28-3746

Alma

North

Alma

Main

North

Palo Alto

Rye

Palo Alto

Harrison

Rye

A-101

A-215

A-201

A-217

A-201

Attributes


27/43


27

A Sample Relational Database


28/43


28

Data Definition Language (DDL)

Specification notation for defining the database schema

E.g.create tableaccount(

account-number char(10),balance integer)

DDL compiler generates a set of tables stored in a data

dictionary

Data dictionary contains metadata (i.e., data about data)

database schema

Data storage and definitionlanguage

language in which the storage structure and access methodsused by the database system are specified

Usually an extension of the data definition language


29/43


29

Data Manipulation Language (DML)

Language for accessing and manipulating the data organized by

the appropriate data model DML also known as query language

Two classes of languages

Procedural user specifies what data is required and how to getthose data

Nonprocedural user specifies what data is required withoutspecifying how to get those data

SQL is the most widely used query language


30/43


30

SQL

SQL: widely used non-procedural language

E.g. find the name of the customer with customer-id 192-83-7465select customer.customer-namefrom customerwhere customer.customer-id= 192-83-7465

E.g. find the balances of all accounts held by the customer with

customer-id 192-83-7465select account.balancefrom depositor, accountwhere depositor.customer-id= 192-83-7465 and

depositor.account-number = account.account-number

Application programs generally access databases through one of

Language extensions to allow embedded SQL

Application program interface (e.g. ODBC/JDBC) which allow SQLqueries to be sent to a database

D b U


31/43


31

Database Users

Users are differentiated by the way they expect to interact with

the system Application programmers interact with system through DML

calls

Sophisticated users form requests in a database querylanguage

Specialized users write specialized database applications thatdo not fit into the traditional data processing framework

Nave users invoke one of the permanent applicationprograms that have been written previously

E.g. people accessing database over the web, bank tellers, clericalstaff

D b Ad i i


32/43


32

Database Administrator

Coordinates all the activities of the database

system; the database administrator has a goodunderstanding of the enterprises information

resources and needs.

Database administrator's duties include:

Schema definition

Storage structure and access method definition

Schema and physical organization modification

Granting user authority to access the database

Specifying integrity constraints

Acting as liaison with users

Monitoring performance and responding to changes inrequirements

T i M


33/43


33

Transaction Management

A transactionis a collection of operations that

performs a single logical function in a databaseapplication

Transaction-management component ensures thatthe database remains in a consistent (correct) state

despite system failures (e.g., power failures andoperating system crashes) and transaction failures.

Concurrency-control manager controls the interactionamong the concurrent transactions, to ensure the

consistency of the database.

St M t


34/43


34

Storage Management

Storage manager is a program module that provides

the interface between the low-level data stored in thedatabase and the application programs and queriessubmitted to the system.

The storage manager is responsible to the following

tasks: interaction with the file manager

efficient storing, retrieving and updating of data

DBMS A hit t


35/43


35

DBMS Architecture

Disk Space Management

Buffer Management

File and Access Methods

Relational Operators

Query Optimizer

Query Parser

Client API

Client

DB

ExecutionEngine

Concurrencyand Recovery

Disk

K I M Hi h


36/43


36

Key Issues: Memory Hierarchy

CPU Cache

Main Memory

Hard Disk

Tape/CD

PriceGoes Up

SpeedGoes Down

ReliabilityGoes Up

D t il d O ll S t St t


37/43


37

Detailed Overall System Structure

Application Architectures


38/43


38

Application Architectures

Two-tier architecture: E.g. client programs using ODBC/JDBC tocommunicate with a databaseThree-tier architecture: E.g. web-based applications, and

applications built using middleware

T D t b G


39/43


39

Top Database Groups

Academia:

1) Stanford University, 2) University of Wisconsin, Madison,3) University of California, Berkeley, 4) University ofMaryland, College Park, 5) University of Washington.

Research Labs:

1) IBM Almaden Research Lab, 2) AT&T Research Labs, 3)Microsoft Research Lab, 4) Lucent Technologies.

Database Products:

1) Oracle, 2) IBM DB2, 3) MySQL, 4) Sybase, 5) MS SQL

Server, 6) Informix.

Database Professionals


40/43


40

Database Professionals

Database implementers

Build modules that go inside the DBMS

Students in ICOM 6005

Database application developers

Build application that run on top of the DBMS, and are used by end-users to interact with their data.


Database Administrators

Create database schema

Maintain and tune the DBMS engine

Maintain and tune the data in the DBMS


Corporations need them ($$$)

SUMMARY


41/43


41

SUMMARY

In this presentation we defined a database as a collection ofrelated data, where data means recorded facts.

A typical database represents some aspect of the real worldand is used for specific purposes by one ormore groups ofusers. A DBMS is a generalized software package for

implementing and maintaining a computerized database. Thedatabase and software together form a database system.

We identified several characteristics that distinguish thedatabase approach from traditional file-processingapplications:

Summary continue


42/43


42

Summary continue..

Existence of a catalog.

Program-data independence and program-operationindependence.

Data abstraction.

Support of multiple user views.

Sharing of data among multiple transactions.

We then discussed the main categories of database users, or the"actors on the scene":

Administrators.

Designers. End users.

System analysts and application programmers.

Summary conti


43/43

Summary conti... We noted that, in addition to database users, there are

several categories of support personnel, or "workers behindthe scene," in a database environment:

DBMS system designers and implementers.

Tool developers.

Operators and maintenance personnel.

We listed some additional advantages of the database approachover traditional file-processing systems:

potential for enforcing standards.

Reduced application development time.

Flexibility.

Availability of up-to-date information to all users.

Economies of scale.

Date post:	05-Apr-2018
Category:	Documents
Upload:	intellectual-kilian
View:	217 times
Download:	0 times

Lecture1mgaya

Documents