ICT｜系統發展生命周期（SDLC）的各個階段 Phases of Systems Development Life Cycle (SDLC)

Phases of Systems Development Life Cycle (SDLC)

System analysis
System design
System implementation
System testing
System conversion
System maintenance

Overview: Tasks involved in each phase

System analysis	System analysts collect users requirements and write system requirement specifications
System design	System analysts design user interfaces and draw flowcharts for the system
System implementation	Programmers write the source codes of the system
System testing	Unit testing, system testing and users acceptance testing are performed
System conversion
System maintenance

System Analysis

The following should be done in the system analysis:

Collecting users’ requirements ^{[DSE 2015 P2D Q2(b)(i), DSE 2018 P2D Q2(c)]}
Conducting feasibility study

Collecting users’ requirements

A system analyst needs to collect the following information:

The function of the system
The users of the system
Major dataflow of the system
Existing hardware and software of the system
Process time and capacity

There are different ways to collect user requirements ^{[DSE 2015 P2D Q2(b)(i), DSE 2018 P2D Q2(c)]}

Interviews
Questionnaires
Observation
Documentation reviews (e.g., documentation of the existing system)

Feasibility study

It is used to assess the effectiveness of various solutions

Three are three aspects of the feasibility study:

Technical feasibility	Evaluate whether the objectives can be achieved using the current level of technologies
Operational feasibility	Evaluate the effects of the system on employees and customers
Economic feasibility	Evaluate using cost and benefit analysis Estimating the costs and the benefits of the system If marginal benefit ≥ marginal cost then implement, else not implement

System Requirement Specifications (SRS)

Requirements include:

Business requirement
Functional requirement
Non-functional requirement

	Functions
Business requirement	Requirements that company needs / functions that the company expected
Functional requirement	What the system must do to fulfill business requirements Emphasizes functions provided by the system e.g., input / output methods
Non-functional requirement	About other aspects of the system apart from the functions e.g., system performance, costs, reliability, security, portability

System Design

Components of a computer-based system

Hardware platform
Software
Inputs
Outputs
User interface
Data (e.g., Database, Data processing, Data control, Data security)
System security

Types of user interface

Command Line Interface (CLI)
Graphical User Interface (GUI)

System design tools

System flowchart
Structure chart
Data flow diagram (DFD)
Data dictionary

Data Flow diagram (DFD) ^{[DSE 2013 P2D Q3(c), DSE 2015 P2D Q4(a)]}

Showing the main requirements of a system
Showing the process, information/data flow in, and out of the system
Showing what data will be stored

Gantt Chart ^{[DSE 2019 P2D Q3(a)(iii),}^{DSE 2021 P2D Q2(d)]}

Usage

Project management

Clarifies the project schedule by illustrating multiple tasks and timelines into a single document^{[DSE 2019 P2D Q3(a)(iii)]}
→ helping project managers to make a realistic assessment of the progress / the completion of time

Showing the dependencies between various tasks and concurrent activities/tasks that are going ^{[DSE 2019 P2D Q3(a)(iii)]}

Supports critical path analysis ^{[DSE 2019 P2D Q3(a)(iii)]}

What is critical path?

A critical path is a sequence of tasks in a project that must be completed in order to ensure that the project is finished on time

System Testing

	Function	Done by who?
Unit test	To ensure that a particular module performs its function as defined in specification / does not contain error	Implemented by developers who write the modules
System test	Implemented by developers who write the modules	Done by developers
Acceptance test	To ensure the system meet the company's users’ requirements Test the system with authentic data	Done by ultimate users to test the system with authentic data

Order of system testing (from the first to the end): ^{[DSE 2017 P2D Q3(c)]}

Unit test → System test → Acceptance test

Supplementary notes: There are three types of system test

Volume test

Functions
To determine whether the system can handle the volume of activities that occur during the peak of processing demands

Storage test

Functions
To test whether the storage capacity of a system can store all transaction data

Performance time test

Functions
To test the length of time used by the system to process data

System Conversion

	Direct cutover conversion	Parallel conversion	Phased conversion	Pilot conversion
Characteristics	^{[DSE 2018 P2D Q2(d)]} The original system is instantly changed to the new system on a given date	^{[DSE 2018 P2D Q2(d)]} Both systems run for some periods at the same time	Different modules of the new system are replaced in different phases	The new system is installed in specific places (pilots, a subset of an organization)
When this conversion should be implemented?	System cannot be run in parallel System is not critical Insufficient resources	The system that cannot tolerate failure / risks made by conversion Important resources for the system are available	Suitable for a large and complex system which is difficult to be implemented in one single phase	Higher risks of the new system and its impacts on the organization are hard to predict
Advantages	^{[DSE 2012 P2D Q2(c)(ii), DSE 2018 P2D Q2(d), DSE 2020 P2D Q4(c)]} Lowest cost of conversion (money, manpower, time) within all conversion No need to manage two systems at the same time	^{[DSE 2019 P2D Q3(a)(iv)]} The risks of conversion is low [The old system can act as a backup, if the new system cannot be operated, operation will not be disrupted] Compare the results / outputs of two systems → easier to find out bugs / errors in the new system	As the conversion is done in parts, time is available for adjustment Lower risks of conversion → impacts of the. failure of new phase will be limited	^{[DSE 2020 P2D Q4(c), DSE 2022 P2D Q3(f)]} Minimizes the impacts on changes → Errors are contained to the first implemented locations only, with limited harmful effects on other places → Reducing the risks of conversion Other places can learn from the experience from pilots, especially in terms of operations
Disadvantages	^{[DSE 2012 P2D Q2(c)(i)]} If there is any problem in the new system → disrupt the operation → the entire system will be affected → higher risks	Parallel run is not feasible under some scenarios Extra resources are needed for running two systems at the same time	If the components of a system is very dependent/integrated, implementing phased conversion will be difficult due to difficulties in dividing into different phases → Increasing the complexity of conversion	Even if the system is run successfully in pilots, it does not mean that other places can be run successfully too

Factors affecting the choice of conversion

Risks
Costs

System maintenance

Why is system maintenance needed? ^{[DSE 2020 P2D Q4(d)]}

Adding / improving more functions/features
Fixing program bugs
Improving security
Improving efficiency

System Documentation

System documentation should be done throughout different stages

System documentation ^{[DSE 2015 P2D Q2(b)(ii), DSE 2022 P2D Q4(d)(ii)]}

	Audience	Function
User manual	Users	Teach users how to use the system
Technical documentation	Developers	Enabling them to understand the system and do the maintenance

Alternative Approaches in System Development

	When to use?	Advantages	Disadvantages
Waterfall model	User requirements are fixed / completed → waterfall model is more systematic	More systematic (Need to complete the previous stage before going to the next stage)	Longer development time Only applicable to projects with clear and frozen requirements
Prototype Approach	Creating a prototype first for a complex system → allowing feedback and insight to be incorporated into the future system	Reducing development time	The prototype may not able to accurately reflect the performance of the actual system
RAD (Rapid application development)	Design and implementation processes are done in an interleave, iterative manner (alternatively) User requirements are not completed / changing → more flexible	Reducing the development time	^{[DSE 2016 P2D Q1(a)(iv)]} Requires sufficient resources (e.g. highly skilled developers) to create the right number of RAD teams If the system cannot be properly modularized, building components for RAD will be problematic Requires user involvement during implementation Lower program re-usability

^{[DSE Practice Paper P2D Q4(e), DSE 2019 P2D Q3(a)]}

Project manager
System analyst
Programmer
Database administrator
Computer operator
Technical support staff

	Main duties
Project managers	Assign resources and roles to members of the development team Set essential milestones of the development plan
System analyst	Communicate with users e.g., collect user requirements Write user requirement specifications Doing system design
Programmer	Code the program Carry out testing