Chapter 5 - Types of Data

File Organization

A presentation by M. Naveed Rajput (ICT Teacher PISJ-ES Jeddah)

Records

A record is an organised collection of information about an object or item

Ted Postlethwaite10 West Hill

Highgate

London

N6 3PY

Fixed or variable length records: pros and cons?

Ted Postlethwaite 10 West Hill Highgate London N6 3PY

Ted Postlethwaite 10 West Hill Highgate London N6 3PY


Pros and Cons: Fixed and

Variable Length Records

Fixed-Length Records Easy to implement

Can predict where records will start and end so faster access

Wastes space

Can be inflexible as space allocated may become too small

Variable-Length Records Uses disk space economically

Flexible

Difficult to implement

Slower access


Data types

Boolean True/False

Integer Whole numbers, e.g. 1, 2, 999

Real Fractional numbers, e.g. 123.456

DateTime Any date- or time-based value, e.g. 29/11/2005,

13:08, 0.001 seconds

String (text) Names, addresses, emails, etc.


File Organization

Describes how records are stored within a file

Three organization methods Serial

Sequential

Random

All other organization schemes are variations of or combinations of these methods


Serial Access

Harris

Shah

Oworu

Tooey

Wickham

Hussein

Heim

Hansen

Schmidt

Arnold

OHanlon

Zachary

Christopher

Records not in order.

Search starts at the beginning of

the file.

Records read in the order that they

are stored.


Records are stored in chronological order (in order as they are input or

occur)

Examples

Recording of telephone chargesATM transactionsTelephone queues


Sequential Access Suitable for applications that require sequential

processing of the entire file

The records in the file are ordered by a search-key Search starts at the beginning of the file


Sequential Organization

Records are stored in order based on a key field

Key field A field containing a value that uniquely identifies a record

ExamplesNamesAccount numbersStudent numbers

Example Phone directories


Every record on the file is processed starting with the first record until EOF is reached

Suppose we only want to access the 4th

record

The 3 records that precede it must be accessed first

Inefficient when records must be processed in a sequence other than their physical order

on the device


Sequential Access Is Efficient

When

A large number of the records on the file must be accessed at any given time


Direct (Random) Access

A high percentage of todays information processing must be done non-sequentially

Records are located by knowing their physical locations or addresses on the

device rather than their positions relative

to other records


Compare Looking for a Recording on

a CD versus on a Cassette Tape

DIRECT

SEQUENTIAL

Data stored on a CD device (direct-access) can be accessed either

sequentially or nonsequentially

Data stored on a tape (sequential access) can be accessed only

sequentially


Types of Files Used by Business

Systems

Temporary

Files

Mirror

FilesArchive

Files


Master Files

Contain the current information for a system

customer file

student file

telephone directory


Table Files

Type of master file Change

infrequently

Stored in a tabular format


Transaction Files

Contain the day-to-day information generated from

business activities

Used to update or process the master file


Temporary Files

Created and used whenever needed by a system


Archive Files

Backup files that contain historical versions of other files


Types of Database

Flat-file database One file

One record per line

Essentially a long list

Relational database Data held in separate tables

Each table relates to an entity in the data model

Tables linked by foreign key relationships


Pros and Cons: Flat-file Databases

Can be very fastSimple to design and implement Inflexible only useful for the

application it was designed for

Data redundancy (same data repeated throughout the database)


Pros and Cons: Relational

Databases

Extremely flexible, can model almost any system

No data redundancyComplex softwareRequires skilled administration

Chapter 5 - Types of Data

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Transcript of Chapter 5 - Types of Data