Overview of Systems Design

CSE1204 - Information Systems 1

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Systems Development Phases

Analysis

Design

Implementation

Review

Maintenance

Quality

Documentation

Ethics

Project Management

Analysts RoleInitiation

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Design (How?)

• Define how the system will be implemented

Select a design strategy and specify

details

VariousSources

Design ideas/opinions

Design Options

System RequirementsSpecification

Report

IMPLEMENTATION

ANALYSIS

SystemVendors Hardware/

Softwaredeals

SystemOwners/Users

Selected Design Option

Design in ProgressReport

Technical DesignReport

Design Phase - Purpose

The main activities of the design phase are: to provide alternative design solutions to assist in the selection of a design solution to acquire the necessary hardware and

software to design and integrate the various physical

system components .. interfaces, security controls, files/databases, etc.

Task 1: Generating Alternative Design Solutions

identify alternatives to fulfil the specified requirements

assess the feasibility of these alternatives alternative solutions should not be limited

to computer solutions: improved manual systems and sub-systems can be equally viable

Define alternatives

prioritise the business requirements from the systems analysis phase (mandatory to desired):

propose different ways to meet the system requirements for various implementation environments• hardware, system software, network platforms

generally three alternatives: low end: conservative in terms of effort, cost and technology high-end: many extra features, functionality not cost primary

focus mid-range … a compromise of the above

Issues to consider in generating alternatives

Constraints • available financial and human resources, required

date, technical (hardware and software etc.), elements of the system that cannot change

• how firm are the constraints? Can they be violated in special circumstances?

• strategic importance of the system

Sources of software • in-house development, hardware manufacturers,

application package producers, custom software producers

Issues to consider in generating alternatives

Outsourcing Hardware and software issues

• is what we have sufficient? can we upgrade?

Implementation issues• what will the level of disruption be? • how long will it take?

Organisational issues• overall cost and availability of funding• will management support the alternative?• will users accept the alternative?

Outsourcing The practice of turning over some or all of

an organisation’s IS applications and/or IT operations to an outside firm.

Why?• May be cost-effective• may be specialist in your business area• to overcome operating problems• running IS not part of core business

need to be aware of the pros and cons

Sources of software

Hardware manufacturers• mainly systems software and utilities

Packaged software producers• range from generic eg. Payroll, to very specific packages e.g. medical

practice software packages Custom software producers

• when internal expertise or personnel not available

In-house development• When resources and staff available and the system must be built from

scratch

Hybrid solutions are common

Choosing off-the shelf software: Process

• identify products which may suit the specified requirements

• Identify criteria for evaluating & selecting products• Solicit proposals from potential vendors (Request

for Proposal)• evaluate and rank vendor proposals• select the best vendor proposal• establish requirements for integrating the

vendor’s products

Request for Proposals The primary purpose of a RFP is to

communicate requirements and desired features to prospective suppliers

The requirements fall into 2 categories• business system requirements• vendor requirements

The requirements must be categorised from mandatory to desirable

Request for Proposal - Outline

Introduction• Background, Brief summary of needs, Explanation of RFP

document, Call for action Standards and instructions

• Schedule of events leading to contract• Ground rules that govern the selection decision

Requirements and features• Hardware, Software, Service

Technical questionnaires Conclusion

Choosing off-the shelf software: Criteria

• Identify criteria by which to evaluate hardware and software

• cost, functionality,vendor support, vendor viability, quality of documentation, ease of learning, ease of use, ease of installation, response time, throughput, version?, ease of customisation, number of current installations, licensing arrangement, training, internal controls, database size limitation, maintenance contracts, customer references

• to help identify criteria you can use• past experience, trade magazines and journals,

information services, potential vendors

Hardware and system software issues

Advantages of using the existing platform:• lower costs• familiarity with system• easier to integrate with current systems• no added cost with converting old systems to new platforms

Reasons for acquiring new hardware or system software• some components of your new system may only run on the new

platform• opportunity to upgrade/expand current technology• may allow for radical change eg. from centralised to distributed

processing

Analyse feasibility of alternative solutions

Once alternative solutions have been identified, they must be analysed for technical, schedule, operational, and economic feasibility

“Feasibility is the measure of how beneficial or practical the development of an information system will be to an organisation”

Whitten et. al. (2001), p 365 Feasibility needs to be assessed throughout the

project

Assessing feasibility

There are four main categories of feasibility tests• Operational .. how well will it work? how do

people feel about it?• Technical .. are the technical resources and

expertise available? is the technical solution practical?

• Schedule .. is the time-table reasonable?• Economic .. how cost-effective is it? Cost

benefit analysis is necessary

2. Select a solution

After alternatives that are infeasible are eliminated, the remaining alternatives are presented to the users in the form of a proposal. This proposal contains:• project plans and size estimates• alternative solutions with associated feasibility

analysis The users then choose the alternative that best

meets their requirements taking into account the recommendation made by the system development project team

3. Acquire hardware and software

• Depending on the solution selected:

• In-house development of custom software• Purchase of commercial software package• Custom software producers: consultants• Hardware and technology platforms

If in-house development: Design the application architecture:

networks, process and data distribution Design the system database and files:

database, file specifications (volumes, records..) Design the system interfaces:

inputs, outputs, dialogue Package the design specifications to guide

programmers during construction phase

Acquiring hardware and software

If software is to be purchased or development is to be outsourced:

Once the proposals have been evaluated and the recommended vendor approved, a contract must be negotiated with the winning vendor: legal and accounting advice is essential at this stage

Specify schedule of delivery Installation must be planned Debriefing of proposals for losing vendors informs them of the

weaknesses in their proposals and retains goodwill in the marketplace.

Acquiring hardware and software

4. Design and integrate the new system

design a user-friendly system that fulfils the system requirements identified in the requirements specification

provide clear and complete technical design specifications to the programmers and technical staff who will construct and implement the system

Application architecure

Need to design the system architecture - the processing, networks, and data:• whether the system will use centralised,

decentralised or cooperative processes• whether the system’s data stores will be

centralised or distributed• how data will be input?• how will outputs be generated?

Factor into design units

Using the process and data models, the target system needs to be factored into design units which:• are easy to build• are easy to test and prove• are easy to maintain• document as a natural by-product• isolate the effect of a given problem• apply principles of re-use• facilitate a large degree of partitioning

Structured Design

breaks complex systems down by partitioning the system into modules, then organising the modules into hierarchies suitable for computer implementation

uses structure charts to communicate the design offers a set of strategies for developing a design

solution from a well-defined statement of the problem

offers a set of criteria for evaluating the quality of a given solution

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Structure Charts

A system is easier to write and test if we divide it into

MODULES

MODULE: A named,bounded, set of statementsto do a single task, havingan identifier by which it canbe referenced as a unit.

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Each of thesemodules iscodedseparately

Design Features

Design features that lead to systems that are easier to maintain and modify: • Small module size .. easier to write and test,

and they are less likely to affected by change• Modular independence (coupling) .. the less the

inside of one module depends upon another, the easier it will be to test and maintain

• Modular strength (cohesion) .. measures the strength of association of elements within a module

Design computer files and/or databases

Files and/or databases must be designed• to maximise performance and flexibility • to adapt to future requirements

Database schema: a map of the records and relationships to be implemented by the database

Consider record sizes, record layouts, storage volume requirements, access requirements, data sharing, security, backup requirements

Internal controls

Ensure controls are in place to restrict access to the data to those who need to know

Include only the data that is necessary Use passwords and different levels of access for different user

groups to limit access Identify a position of responsibility for ensuring privacy, allocating

new passwords, checking logs for unauthorised access Data, programs, ideas and knowledge are all valuable assets to

the owner: unauthorised access, loss or corruption may cause significant loss or penaltye.g. the tax file number is owned by the Commonwealth and its use as a primary key is forbidden by law

Backup and Recovery

a standard system of controls that should be built into all systems

principles:• data can be reconstructed in the event of loss

or corruption• application and system software can be

reinstated in the event of loss or corruption loss or corruption may be deliberate or

accidental - controls are essentially the same

Design computer outputs and inputs and on-line interfaces

the precise format and layout of all outputs must be specified: may be on paper, pre-printed forms or screens

the data capture method for all inputs must be specified: initial manual capture and/or direct entry into the computer system

build easy-to-learn and easy-to-use dialogue around the input and output screens designed in earlier tasks

End-users and managers must be involved: their requirements, opinions and feedback

Prototyping is useful

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Human–Computer Interface Design

INTERFACE

INTERFACE

ProgramsProgramsDatabase

end userdirect user

The interface is the link between the users and the computer

To many users the interface is the system

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Interface and dialogue design the process of defining the manner in which

humans and computers exchange information analogous to a conversation between 2 people interface and dialogue design is critical for

successful information systems “to the user the interface is the system” should provide a uniform structure for finding,

viewing, and invoking different components of an information system

Inputs and outputs: forms and reports form and report design are key ingredients for

successful information systems - especially for users

each input data flow to a process will be associated with a form

each output data flow from a process will be associated with either a form or a report

forms and reports can be paper-based or screen-based

Forms and reports A FORM is a business document containing some

predefined data and also some areas for other data to be filled in

typically based on one database record a turnaround document is produced as an output

by a system and then returned with input data

A REPORT is a business document that contains only predefined data: a passive document for reading

typically contains data from many different database records

Inputs and outputs Outputs present information to users: Internal outputs:

• Detailed reports, summary reports, exception reports External outputs:

• E.g. invoices, statements, turnaround documents Input design involves:

• How the data is initially captured, entered and processed

• The method and technology used to capture and enter the data

• Controls for accuracy of input data

Design guidelines

Consistency - of operation efficiency - related to user task ease - output self explanatory format - consistent format between

entry and display flexibility - must be convenient to user

Usability typically refers to: speed - efficient completion of task accuracy - output provides what is expected Satisfaction - output is liked

References

WHITTEN, J.L., BENTLEY, L.D. and DITTMAN, K.C. (2001) 5th ed., Systems Analysis and Design Methods, Irwin/McGraw-HilI, New York, NY.

Chapters 9, 10

HOFFER, J.A., GEORGE, J.F. and VALACICH (1999) 2nd ed., Modern Systems Analysis and Design, Benjamin/Cummings, Massachusetts.

Chapter 11