Introduction to Computing: Lecture 6 - Dr. Pham Tran Vu

Introduction to Computing: Lecture 6 - Databases presents about The Hierarchy of Data, Keys and Attributes, The Traditional Approach To Data Management, Database, Database Approach, Traditional Files vs. Databases, Database Management Systems.

Databases

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The Hierarchy of Data

Hierarchy of data Example

, 005 - 10 - 6321 Johns, Francine 10-07-1997

| ; (Record containing

098 - 40 - 1370 Fiske, Steven 01-05-1985 : son fast and first

name, hire date)

Keys and Attributes

Employee # | Lastname First name Hire date Dept number 005-10-6321 Johns Francine 10-07-1997 257 549-77-1001 Buckley Bill 02-17-1979 632 098-400-1370 Fiske Steven 01-05-1985 598

7 Key field

Aiwlxsse

(fields)

Entities (records)

Database

Oo “A collection of data, generally related to

some subject or topic area and structured so

as to allow relationships to be established between separate data items accoraing to the various needs of users”

G Knott & N Waites, Computing 3" edition

đễ:w Tradiional Files vs Databases:

Pros and Cons

5m Database Management Systems

(DBMS)

o Databases are usually managed by DBMS

o DBMS: A collection of programs that controls and

prevents accidental or deliberate corruption of data

by other application programs

o Functions of DBMS

=» dStore, query and update data

=» Manage transaction

=» Control concurrent access to database

=» Maintain data consistency and integrity

Relational Database Model

Data table 1: Project table

Relational Models

o Describe data using a standard tabular format

with all data elements placed in two- dimensional tables, called relations, that are

the logical equivalent of files

» Domain

=» selecting

=» Projecting a» Joining

BK Linking Database Tables to Answer

Oo Single key: composed of only one attribute

co Composite key: composed of two or more

attributes

o A table can have many keys

Oo Primary key: a selected key

o Candidate keys: other keys, except primary key

Foreign Keys

oO If atable uses the primary key of another

table as attribute to refer to a row in the other table, the attribute is called referential

key or foreign key

— Ss Foreign Key (implements 1:N

Order_!ID Order Date ( Customer_!ID — lati hip bet t d

— "_— —— relationship between Customer an

order)

ORDER LINE Combined, these are a composite

| primary key (uniquely identifies the Korert® Croduo 2 ) Ordered_Quantty | order line) individually they are

+ foreign keys (implement M:N

relationship between order and PRODUCT product)

Product_ ID Product_Description | Product Finish | Standard_ Price | Product Line ID

Database Design and Construction

Data Modelling

Oo To analyse and moael the logical structures

and relationships between data items

Oo To assist the data design process

o Entity Relationship Model is commonly used

as a data modelling tool

=» Convert entities into tables

=» Identify keys and attributes

=» Create referential keys (foreign keys) for

relationships

o Decide data types and length for attributes

Data Normalisation

Oo A step-by-step process for analysing data

into its constituent entities and attributes

o To improve database efficiency and to

maintain data consistency and integrity

Oo Commonly, three normal forms are used:

a First normal form (1NF)

=» second normal form (2NF)

=» Third normal form (3NF)

Database Construction

o Use tools, eg MS Access

o Use Structured Query Language (SQL)

=» Data Definition Language

o for defining database and database tables

o Commands: create database, create table, alter table,

drop table, etc

» Data Manipulation Language

o For manipulating the data within data

o Commands: select, insert, update and delete

Distriouted Databases

o In distributed database system, the

database is subdivided over multiple computer systems but appear to users