1. Large Scale Systems Design G52LSS
Lecture 2 – Large Systems Development
Phases of the SDLC
Methodologies for SDLC
Selecting Methodologies
Learning outcomes: describe phases, steps and deliverables of the SDLC; understand the different structured and non-structured SDLC methodologies; appreciate advantages and disadvantages of the different SDLC methodologies.
Large Scale Systems Design
Dr Colin Higgins

2. Large Scale Systems Design
Phases of the SDLC
The Systems Development Life Cycle is a gradual refinement process traditionally consisting of 4 phases:
Planning
Analysis
Design
Implementation
Each phase is composed of steps that rely on techniques
Each step is meant to produce a specific deliverable
Why?
What? When? Where? Who?
How?
Delivery
Large Scale Systems Design
Dr Colin Higgins

3. Planning Phase Opportunity Identification System Request
Feasibility Analysis
(technical, economic, organisational)
Project Management
Planning Phase. Why to build the System?
Opportunity Identification. Solve a problem, improve, innovate.
System Request. Describe business need and how the system will create value.
Feasibility Analysis. Can the system be built? What is the value? Will the system be used?
Project Management. Scheduled times, staff committed, management techniques.
Project Workplan. Describes how the development team will approach the project.
Project Workplan
Large Scale Systems Design
Dr Colin Higgins

4. Analysis Phase Develop Analysis Strategy Define Requirements
Use Cases, Process Model, Data Model
Analysis Phase. What system will do? who/when/where will use the system?
Develop Analysis Strategy. Towards comparing new system with the old one.
Define Requirements. Gather information with interviews, questionnaires, document analysis, JAD, etc. Define functional and non-functional requirements.
Systems Proposal. Describes analysis but also an initial high level design. Identifies clear business requirements.
Systems Proposal
Large Scale Systems Design
Dr Colin Higgins

5. Large Scale Systems Design
Design Phase
Design Selection
Architecture Design
Interface Design
Data Storage Design
Program Design
Design Phase. Determine exactly how the system will work.
Design selection. Outsourcing? Buy design software? Commercial of the shelf software (COTS)?
Architecture design. General infrastructure.
Interface design. User oriented.
Data storage design. Information oriented.
Program design. Coding components.
System specification. Describes in a technical manner how the system should be implemented.
System Specification
Large Scale Systems Design
Dr Colin Higgins

6. Large Scale Systems Design
Implementation
System Construction
Installation Process
Support Plan
Implementation. Deliver the system to users.
System Construction. Building and testing, adequate testing is critical.
Installation Process. Replace current system, training users, training plan is required
Support Plan. Changes and maintenance, maintenance estimated to account for 48-60% of the time.
Functional, efficient and robust system. The system delivered should be fit for purpose.
Functional, Efficient and Robust System
Large Scale Systems Design
Dr Colin Higgins

7. Methodologies for SDLC
Structured Design
Waterfall development
Parallel Development
Rapid Application Development
Phased Development
Prototyping
Throwaway Prototyping
Agile Development
Extreme programming
Other agile methodologies include: Crystal, Scrum, Adaptive Software Development, Dynamic Systems Development, Feature Driven Development.
Formal step-by-step approach
Focuses on quick development
Eliminates modelling and documentation overhead
These methodologies have Advantages and Disadvantages with respect to:
Development time
Resources needed
Documentation required
Adaptability/evolution
Large Scale Systems Design
Dr Colin Higgins

8. Large Scale Systems Design
Waterfall Development Diagram from (Dennis et al. 2006)
Sequential process
Pros
System requirements are identified well in advance to programming
Minimises changes to requirements as project progresses
Cons
Design must be specified on paper before programming begins
Long time between system proposal and delivery of new system
Significant rework if changes needed
Large Scale Systems Design
Dr Colin Higgins

9. Large Scale Systems Design
Parallel Development Diagram from (Dennis et al. 2006)
Division into subprojects
Pros
Tries to reduce schedule time
Less chance of rework
High level design
More specific designs
Cons
Uses paper documents
It is difficult to integrate subprojects
Large Scale Systems Design
Dr Colin Higgins

10. Large Scale Systems Design
Phased Development Diagram from (Dennis et al. 2006)
Versions-based process
Pros
First system delivered quickly
User can identify additional needs for later versions
Cons
The user works with an intentionally incomplete system
Large Scale Systems Design
Dr Colin Higgins

11. Large Scale Systems Design
Prototyping Diagram from (Dennis et al. 2006)
Performs phases concurrently and repeatedly
Pros
Prototype delivered quickly
User can identify changes in needs and requirements can be refined
Prototype (not a 1st version)
Concurrently
Cons
Risk of superficial analysis
Poor initial design decisions
User tries a finished system
Large Scale Systems Design
Dr Colin Higgins

12. Large Scale Systems Design
Throwaway prototyping Diagram from (Dennis et al. 2006)
Uses disposable design prototypes
Pros
Helps to minimise risks
Understand important issues before proper design
Cons
Needs more time than prototyping
High level design
Concurrently
Not fully working system
Large Scale Systems Design
Dr Colin Higgins

13. Large Scale Systems Design
Extreme Programming Diagram from (Dennis et al. 2006)
System grows iteratively
Pros
Results delivered fast
Good for projects with undefined and changing requirements
Cons
Requires considerable input from users
Requires great discipline
Large Scale Systems Design
Dr Colin Higgins

14. Large Scale Systems Design
Exercise 2.1 Suppose you are a project manager using the waterfall development methodology on a large and complex project. Your manager has just read a recent article in a magazine that advocates replacing the waterfall methodology with prototyping and comes to your office requesting you to switch approaches. What would you say? Exercise taken from (Dennis et al. 2006)
Justify the use of waterfall methodology for current project considering the strengths of that approach.
Consider if prototyping would really be better for this scenario, so questions like the following need to be asked:
users are available?
risk of poor analysis and design?
time available for development?
Large Scale Systems Design
Dr Colin Higgins

15. Selecting Methodologies
Difficult because no methodology is always the best
Standards and practices vary between organisations
Important criteria are the following
Ability to develop systems that… WF PA PH PR TP XP
Unclear requirements
Unfamiliar technology
Complex
Reliable
Short schedule
Schedule visibility
P P G E E E
P P G P E P
G G G P E P
Unclear requirements. Then the user should interact with the system to understand what it can do.
Unfamiliar technology. Then users should have time to get used to the system being developed.
Complex. Then careful and detailed analysis is required to consider all details.
Reliable. If crucial then good analysis and design is required in addition to test under different conditions.
Short schedule. Then development should be speedup and should accommodate adjustments.
Schedule visibility. Important to know if the project is on track and on time.
G G G P E G
P G E E G E
P P E E G G
Large Scale Systems Design
Dr Colin Higgins

16. Large Scale Systems Design
The above methodologies can also be combined to produce hybrid SDLC methodologies that would be more adequate for certain project development scenarios.
Exercise 2.2 Suppose you were to combine throwaway prototyping with parallel development. What diagram would illustrate the hybrid methodology? What would be the pros and cons of the hybrid methodology? Exercise taken from (Dennis et al. 2006)
Large Scale Systems Design
Dr Colin Higgins

17. Large Scale Systems Design
Exercise 2.2 (cont.)
Ability to Develop Systems… Hybrid Methodology
With Unclear User Requirements Good
With Unfamiliar Technology Good
That are Complex Excellent
That are Reliable Excellent
With a Short Time Schedule Good
With Schedule Visibility Good
Large Scale Systems Design
Dr Colin Higgins

18. Large Scale Systems Design
Additional Reading
Chapter 1 of (Dennis, Wixom and Roth, 2006)
Chapter 1 of (Kendall and Kendall, 2005)
Large Scale Systems Design
Dr Colin Higgins