1. Chapter 2 Software Process Models

2. Process Models Often referred to as “conventional” process models
Prescribe a set of process elements
Framework activities
Software engineering actions
Tasks
Work products
Quality assurance and
Change control mechanisms for each project
There are a number of process models in operation
They are not perfect but they provide a useful roadmap for SW engineering work
Each process model also prescribes a workflow

3. A Generic Process Model

4. Process Flow

5. Build & Fix Model Product is constructed without specifications
or any attempt at design
Adhoc approach and not well
defined
Simple two phase model

6. Build & Fix Model
Suitable for small programming exercises of 100 or 200 lines
Unsatisfactory for software for any reasonable size
Code soon becomes unfixable & unenhanceable
No room for structured design
Maintenance is practically not possible

7. The Waterfall Model Sometimes called classic life cycle
Suggests a systematic, sequential approach to software development
It reinforces the notion of “define before design” and “design before code”.
Works best when
Requirements of a problem are reasonably well understood
Well-defined adaptations or enhancements to an existing system must be made
Requirements are well-defined and reasonably stable

8. The Waterfall Model This model is named “waterfall
model” because its diagrammatic
representation resembles a cascade of waterfalls.

9. The Waterfall Model - Problems
It is difficult to define all requirements at the beginning of a project
This model is not suitable for accommodating any change
A working version of the system is not seen until late in the project’s life
It does not scale up well to large projects.
Real projects are rarely sequential.

10. The Incremental Model
It combines elements of the waterfall model applied in an iterative fashion
It delivers a series of releases, called increments, that provide progressively more functionality for customer as each increment is delivered
When it is used, the first increment is often a core product. That is, basic requirements are addressed, but many supplementary features remain undelivered
The core product is used by customer. As a result, a plan is developed for next increment

11. The Incremental Model

12. The Incremental Model
This model focuses on the delivery of an operational product with each increment
Incremental development is particularly useful when staffing is unavailable for a complete implementation by the business deadline. Early increments can be implemented with fewer people, and additional staff can be added to later increments
Increments can be planned to manage technical risks

13. The RAD Model
RAD (Rapid Application Development) is an incremental SW process model that emphasizes a short development cycle
RAD model is a “high-speed” adaptation of the waterfall model, in which rapid development is achieved by using a component-based construction approach
If a business application can be modularized in a way that enables each major function to be completed in less than 3 months, it is a candidate for RAD
Each major function can be addressed by a separate RAD team and then integrated to form a whole

14. The RAD Model

15. The RAD Model
Developed by IBM in 1980
User participation is essential

16. The RAD Model With active participation of users
Build a rapid prototype
Give it to user for evaluation & obtain feedback
Prototype is refined
With active participation of users

17. The RAD Model - Drawbacks
Not an appropriate model in the absence of user participation.
For large, but scalable projects, RAD requires sufficient human resources to create right number of RAD teams
Highly specialized & skilled developers are are not easily available.
If a system cannot be properly modularized, building the components necessary or RAD will be problematic
Reusable components are required to reduce development time.
RAD may not be appropriate when technical risks are high

18. Evolutionary Process Models
Evolutionary models are iterative
They are characterized in a manner that enables SW engineers to develop increasingly more complete versions of the software
Example models
Prototyping model
The Spiral model
Concurrent model

19. Evolutionary Models: Prototyping
The prototype may be a usable program but is not suitable as the final software product.
The code for the prototype is thrown away. However, experience gathered helps in developing the actual system.
The development of a prototype might involve extra cost, but overall cost might turnout to be lower than that of an equivalent system developed using the waterfall model.

20. Evolutionary Models: Prototyping

21. Evolutionary Models: Prototyping
The customer sees what appears to be a working version of SW, unaware that in the rush to get it working we haven’t considered overall quality or long-term maintainability
The developer often makes implementation compromises in order to get prototype working quickly

22. Evolutionary Models: Spiral
Couples the iterative nature of prototyping with the controlled and systematic aspects of the waterfall model
It provides the potential for rapid development of increasingly more complete versions of the software
It is a risk-driven process model generator
It has two main distinguishing features
Cyclic approach
Incrementally growing a system’s degree of definition and implementation while decreasing its degree of risk
A set of anchor point milestones
A combination of work products and conditions that are attained along the path of the spiral

23. Evolutionary Models: Spiral

24. Evolutionary Models: Spiral
Unlike other process models that end when software is delivered, the spiral model can be adapted to apply throughout the life of the computer s/w
The circuits around the spiral might represent
Concept development project
New Product development project
Product enhancement project
The spiral model demands a direct consideration of technical risks at all stages of the project

25. Evolutionary Models: Spiral
Difficult to convince customers that evolutionary approach is controllable
Demands considerable risk assessment expertise and relies on this expertise for success
If major risks are uncovered and managed, problems will occur

26. Evolutionary Models: Concurrent
Sometimes called concurrent engineering
Can be represented schematically as a series of framework activities, s/w engineering actions and tasks, and their associated states
Defines a series of events that will trigger transitions from state to state for each of the s/w engineering activities, actions, or tasks
Defines a network of activities
E. g. The modeling activity which existed in none state while initial communication was completed, now makes a transition into under development state. If customer indicates that changes in requirements must be made, modeling activity moves from under development state into awaiting changes state

27. Evolutionary Models: Concurrent

28. Evolutionary Models: Concurrent
Is applicable to all types of software development and provides an accurate picture of the current state of project
All activities exist concurrently but reside in different states
Events generated at one point in the process network trigger transitions among the states

29. Other Process Models
Component-based development—the process to apply when reuse is a development objective
Formal methods—emphasizes the mathematical specification of requirements
AOSD—provides a process and methodological approach for defining, specifying, designing, and constructing aspects
Unified Process—a “use-case driven, architecture-centric, iterative and incremental” software process closely aligned with the Unified Modeling Language (UML)

30. The Unified Process (UP)
Developed by I.Jacobson, G.Booch and J.Rumbaugh
It is a use-case driven, architecture-centric, iterative and incremental software process
UP is an attempt to draw on the best features and characteristics of conventional s/w process models
Also implements many of the best principles of agile software development
UP is a framework for object-oriented software engineering using UML (Unified Modeling Language)

31. Phases of The Unified Process

32. Phases of UP - Inception
Defines scope of the project
Encompasses both customer communication and planning activities
Fundamental business requirements are described through a set of preliminary use-cases
A use-case describes a sequence of actions that are performed by an actor (e.g., a person, a machine, another system) as the actor interacts with the software
A rough architecture for the system is also proposed

33. Phases of UP - Elaboration
Encompasses customer communication and modeling activities
Refines and expands the preliminary use-cases
Expands the architectural representation to include five different views of the software
The use-case model
The analysis model
The design model
The implementation model
The deployment model
In some cases, elaboration creates an “executable architectural baseline” that represents a “first cut” executable system

34. Phases of UP - Construction
Makes each use-case operational for end-users
As components are being implemented, unit tests are designed and executed for each
Integration activities (component assembly and integration testing) are conducted
Use-cases are used to derive a suite of acceptance tests

35. Phases of UP - Transition
Involves many activities like delivering, training, supporting, and maintaining the product.
Software is given to end-users for beta testing
The software team creates the necessary support information
User manuals
Trouble-shooting guides
Installation procedures
At the conclusion of the transition phase, the software increment becomes a usable software release

36. Phases of UP - Production
Coincides with the deployment activity of the generic process
The on-going use of the software is monitored
Support for the operating environment (infrastructure) is provided
Defect reports and requests for changes are submitted and evaluated

37. Unified Process Work Products
Inception
Vision document
Initial use-case model
Elaboration
Analysis model, design model
Construction
Implementation model, deployment model, test model
Transition
Delivered software, beta test reports, general user feedback

38. Initial Development & Evolution Cycles

39. Iterations & Workflow of Unified Process

40. Selection of a Life Cycle Model
Selection of a model is based on: a) Requirements b) Development team c) Users d) Project type and associated risk

41. Based On Characteristics Of Requirements

42. Based On Status Of Development Team

43. Based On User’s Participation

44. Based On Type Of Project With Associated Risk