L1- System Analysis

Software Development Cycle

Analysis → Design → Implementation → Evaluation → Maintenance → (cycle repeats)

Analysis Stage

1. Systems analyst gathers information about what the current system does/if there is one, and what the new systems needs to do

2. To get this information, the systems analyst may:

3. interview people who will use the software

4. use questionnaires to get information from large groups of people

5. observe how the current system works

6. look at existing documentation

Output from Analysis

Systems analyst will produce a decent called something like ‘System Specification’ / ‘User Requirements’

This document defines WHAT the system will do but not HOW it will do it- it is used to create the design and to evaluate the finished product

Design Stage

Software design will include:

1. a description of data: data type, format, and validations

2. database design (if appropriate)

3. input screens

4. output screens & reports

5. how the data will be processed

6. how the software will be tested

Implementation Stage

this stage includes:

1. coding and testing the software

2. writing user and technical documentation

3. installing the software for the user

Testing Strategies

1. Black box testing- carried out independently of the code used in the program- it looks at the program specification and creates a set of test data that covers all the inputs, outputs, and program functions

2. White box testing- depends on the code logic- tests are devised which test each path through the code at least once

3. Alpha testing- carried out by the software developer's in-house team and by the user- can reveal errors/omissions in the definition of the system requirements- user may discover that the program doesn’t do what they want it to do

4. Beta testing- this is when commercial software is being developed (e.g. Ms Windows, Ms Word, etc)- the software is given to a number of potential users, who agree to use the software and report any faults

Evaluation stage

the user now needs to test every aspect of the software to make sure it does what it is supposed to

it is evaluated against the original specification document

this can also be called acceptance testing

Maintenance stage

1. Corrective maintenance- bugs will usually be found when software is put into action, no matter how thoroughly it was tested

2. Adaptive maintenance- over time, user requirements may change and the the software will have to be adapted to meet those requirements

3. Perfective maintenance- even if the software works well, there may be ways of making it even better- faster, easier to use, more functionality, etc.

And then the cycle repeats!

Waterfall model

1. each stage is completed and documented before moving on to the next one

2. customer does not see the end product before it is completed

3. any changes means the project has to start all over again

Advantages of waterfall model

1. simple to understand and use

2. each stage is separate and self-contained with well defined outcomes and written documentation

3. this makes the project relatively straightforward to manage

4. model works well for smaller projects where requirements are very well understood

Disadvantages of waterfall model

1. not much user involvement after the analysis stage

2. no working software is produced until late in the cycle

3. user is presented with finished product and if they don’t like it, it’s too late to make changes

when is the waterfall model suitable?

1. requirements are clear and fixed

2. no ambiguous requirements

3. technology is well understood

4. project is short

Spiral model

Four basic stages of development (A, D, I, E) are followed

software project passes through these phases repeatedly

each successive loop generates a new. more refined prototype until the software meets the user’s requirements

Advantages of the spiral model

1. well defined steps make the project easy to manage

2. software is produced at an early stage so problems and issues can be identified early

3. user gives feedback to each prototype and any changes can be made early in the process

4. added functionality can be added during the process

5. end result is more likely to be what the user wants