information system 2

Information System Development

INFROMATION SYSTEM PART 2 BY SUJITH BHASKAR R

http://blog.centreetech.com/




Feasibility

Analysis

Design

Implementation

Test

Maintain

SDLC - Classic Waterfall model



Prototype

A prototype is a working system to explore implementation or processing alternatives and evaluate results

•SDLC takes too long•The right system is rarely developed the first time


Prototype are used when ……

• No system of the proposed type has been constructed so far

• Essential features of the system are partially known and they are not identifiable even after careful analysis of the existing system

• Using the system will add to requirement lists

• Alternate systems will evolve through experience

• User participation very effective


Steps towards prototyping

• Identify the user requirements

• Develop a working prototype.

• Allow the user to use the prototype and collect feedbacks

• Modify the existing prototype incorporating the feedbacks

• Repeat for the next version …..


RAD (RAPID APPLICATION DEVELOPMENT)

• Planning

• Analysis

• Design

• Build

• Test

• Deploy

Compressed


RADAdvantages

• Increased speed of development

• Increased quality

Disadvantages

• Reduced scalability

• Reduced features


Requirement Analysis – requirements definitions and gathering

• Requirement elicitation (gathering customer needs)

• Requirement analysis (understanding a problem and requirements of a workable solution)

• Requirement specification (description of what the system will do) should be complete, comprehensive, testable, consistent, unambigous,writable, modifiable and implementable.

• Requirements management (process that helps the team to identify, control and track changes)


Logical Design

• Define boundaries

• Inputs

• Outputs

• Data stores

• Procedures

DESIGN OF A SYSTEM

Physical Design

• Input / Output Media

• Database design

• Decide software platforms

• Implementation plan

• Testing procedures


• Flowcharts

• Data flow diagrams (DFD’s)

• Data dictionary

• Structured English

• Decision table

• Decision tree

Tools for System Design


Flowcharts are pictorial representation of program logic.

• Shows step by step solution to a problem

• Easy to understand graphical representation

• Provides clear documentation

• Is complex for larger problems

Flowcharts


Symbols in Flowcharts

Y N

Start / Stop

Input / output

Decision Box

Process Box

Flow of Control

Connectors


Flowcharts

Start

Input A,B

Is A > B

Print BPrint A

Stop

Y N


DFD is a structured diagrammatic technique for showing the functions performed by a system and the data flowing into, out of and within it.

Data Flow Diagrams (DFD’s)

DFD’s Show ……

• The processes within the system

• The datastores (files) supporting its operation

• The information flows within it

• The system boundary

• Interactions with external entities


Customer

Sales1Order

Rejected Order

Dispatch Note

2 Warehouse

Dispatch Goods

3 Accounts

Maintain Credit Ratings

D1 Credit Rating

Check Credit Rating

A Complete DFD


Customer

Sales

Check Credit Rating

D1 Credit Rating

A Data Flow

An External Entity

A Process

A Data Store

3DFD Symbols


Sales

Check Credit Rating

3

Unique Number Where it’s done

What’s done

Output DataInput Data

The Process Symbol


Customer

D1 Credit Rating

A Duplicated External Entity

Duplicated Data Store

Customer

Repeated Symbols – to avoid crossing lines, data

stores and external entities can be repeated:

D – Computerised Data file M – Manual file


A wines and spirits wholesaler stocks a range of approximately 400 different lines and delivers by van on regular weekly runs to customers who are mainly off-licenses and clubs. The majority of orders are received by telephone and any one customer may place several orders during the week which must be accumulated and delivered in one consignment. When a customer telephones he expects to be advised on the availability of an item requested and, if not in stock, the alternatives that are available. At present, sales order forms are filled in by the telephone salesmen and sent to the warehouse where they are used for the despatch of the items. Hand-written despatch notes are used as the basis of the invoices which are typed and sent by post sometime later.

Prepare a dataflow diagram (DFD) which represents the above system.


customer

customer

Stock file

Accumulate orders

Advise availability

Complete forms

1 Sales

Sales Order Forms

2

Produce despatch notes

Produce Invoices

InvoiceDespatch note + goods

Warehouse

The DFD

Order Advice

M1


This is a catalog or a repository of data about data (Metadata). A list of all the elements composing the data flowing through the system will be found here. The major elements are data flows, data stores and processes.

Data Dictionary


Is a modified form of the English language used to specify the logic of information system processes. Although there are no standards, Structured English normally relies on action verbs and noun phrases and contains no adjectives or adverbs

Structured English


Are used to lay out all possible situations which a business decision may encounter and to specify the action to be taken in each of the situation in a tabular form.

Decision Table

Printer troubleshooter

Rules

Conditions

Printer does not print Y Y Y Y N N N N

A red light is flashing Y Y N N Y Y N N

Printer is unrecognised Y N Y N Y N Y N

Actions

Check the power cable X

Check the printer-computer cable X X

Ensure printer software is installed X X X X

Check/replace ink X X X X

Check for paper jam X X


A decision tree is a diagram that represents conditions and actions sequentially and thus shows which conditions to consider first, which second and so on.

Decision Tree


• How to execute the package

• How to enter data

• Processing details

• Generating reports

Implementation and Maintenance


• Parallel run

• Pilot run / Phased run

Implementation and Maintenance

Overall Evaluation

• Operational

• Organisational

• User Manager assesment

• Development performance


Make or Buy Decision for Information systems

Packaged solutions Custom-built solutions

Hybrid solutions

What it means Complete solution provided by a vendor

Custom build / Tailor made from scratch

Partially packaged / partially custom built

Potential benefits

• Cheaper • Quality• Future migrations

• Better fit• More control• Fine tuned

• Best of solutions• Customization

Potential risks • Stability of Vendor• Process changes• Experience

• Immature skills• Time factor• Future changes

• Skill set issues• Integration• Vendor experience

Costs to consider

• License• Support• Training• Quality assurance

• Infrastructure• Development• Technology• Quality assurance

• License• Support• Training• Development

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