week 4 advantages over flat file

8/6/2019 Week 4 Advantages Over Flat File

1/19

Prevalent Database Models

(Advantages of a database over

flat files)


2/19

FLAT file system

Ordinary operating system files

Contain no information to communicate the file

structure or any relationship between files

This information must be provided by the

application programme..or the user.

Do not meet the definitions of a database we

identified earlier. Flat Files are often used to store database

information

Address File House number Street Town


3/19

FLAT file system (2)

If flat files are used to store database data

the DBMS has metadata to allow it to

translate data from the physical (flat file)into the logical layer format

Flat file systems quickly become

cumbersome and difficult to maintain

(see pages 7, 8 and 9 of course text book)


4/19

Flat Files

Here are someflat files grouped

together by type

you can see

the repeatingformat


5/19

The Hierarchical Model (1)

Similar to an organisation chart

Think of the way we structure our personal

computer files into directories andsubdirectories


6/19

Hierarchical Model (2)

Records are connected using pointers

The pointer tells the system where the

related record is physically stored ..Much as a street address tells us where a

particular building is .. Or a URL directs

us to a particular webpage

Each pointer establishes a parent-child

relationship


7/19


8/19


There are problems associated with setting

up and maintaining this type of database

caused by the parent-child relationship

(see the text book for a detailed

explanation)


9/19

Hierarchical model (5)

Consider this typical

business situation:-

a customer can placemany orders

An order can contain

many details

These are clearly one-to-many relationships

CUSTOMER

ORDER

ORDER

DETAIL


10/19


But most business

would also recognise

that:-

An employee can be

associated with many

orders

A product can bespecified in many order

details

CUSTOMER

ORDER

ORDER

DETAIL

EMPLOYEE

PRODUCT


11/19


But if we try and show thislogical linkage we break one ofthe fundamental rules of theparent child relationship.each child can only haveone parent

There are ways of resolving thisdilemma, but they introducecomplexity into the constructionand maintenance of the

database . Something wewant to avoid

(see the text book for a detailedexplanation)

CUSTOMER

ORDER

ORDER

DETAIL

EMPLOYEE

PRODUCT


12/19

Network Model

In some ways similar to the hierarchical model inthat pointers are used to link files.

Pathways are more numerous and can bethought of as circular which quickly leads tocomplexity

Rather like walking through a forest withmultiple pathways to get to the desireddestination.

Maintenance overhead for technicians inkeeping the route map up to date becameprohibitive


13/19

Network Model

beware of complex pathways!

CUSTOMER

ORDER

EMPLOYEE

ORDERDETAILS

PRODUCTS

NEXT

CUSTOMER

NEXT ORDER

FOR

THIS EMPLOYEE

OTHER ORDERS

FOR

THIS PRODUCT

(see the text book for a detailed explanation)


14/19

The RELATIONAL Model

Was a truly revolutionaryapproach

Flexible, no pre-defined pathways

Ideal for ad hoc queries Relates records as they are needed

Instead of pointers locating physical filelocations common data items (keys) are

used to identify logical links betweenrecords

Uses the one-to-many concept


15/19


The diagramming technique is known as

the entity-relationship diagram (ERD)

CUSTOMER

ORDER

ORDER

DETAIL

CUSTOMER

CUSTOMER

These are the

entities .. Things

that the business

wishes to keep

information about


16/19


CUSTOMER

ORDER

ORDER

DETAIL

EMPLOYEE

PRODUCT

The lines show the connections between the entities and

express the one-to-many relationship

The M denotes

the many end ofthe relationship1

m

1

m1

m

m 1


17/19


This introductory module will focus around

the RELATIONAL model

We will look at how to draw ERDs Refine them

Implement them as databases that can

function to supply real information fromraw data.


18/19

Database Models

The Object Oriented model (4)

This is a newer model that uses the

idea of objects to store data.

This model is not yet fully implemented

but much research is going into its

development.


19/19

Summary We have looked at the four database

models

Hierachical

Network

Relational Object oriented

week 4 advantages over flat file

Documents