Pressman ch-3-prescriptive-process-models

Chapter 3
Prescriptive Process
Models

- Generic process framework (revisited)
- Traditional process models
- Specialized process models
- The unified process

Generic Process Framework

 Communication
 Involves communication among the customer and other stake holders;
encompasses requirements gathering
 Planning
 Establishes a plan for software engineering work; addresses technical
tasks, resources, work products, and work schedule
 Modelling (Analyze, Design)
 Encompasses the creation of models to better under the requirements and
the design
 Construction (Code, Test)
 Combines code generation and testing to uncover errors
 Deployment
 Involves delivery of software to the customer for evaluation and feedback

2

Modeling: Software
Requirements Analysis
 Helps software engineers to better understand the problem they
will work to solve
 Encompasses the set of tasks that lead to an understanding of
what the business impact of the software will be, what the
customer wants, and how end-users will interact with the
software
 Uses a combination of text and diagrams to depict requirements
for data, function, and behavior
 Provides a relatively easy way to understand and review
requirements for correctness, completeness and consistency

3

Modeling: Software Design

 Form the “blueprint” for a product
 Creates a model that that provides detail about software data structures,
software architecture, interfaces, and components that are necessary to
implement the system
 Architectural design
 Represents the structure of data and program components that are required
to build the software
 User Interface Design
 Creates an effective communication medium between a human and a
computer
 Component-level Design
 Defines the data structures, algorithms, interface characteristics, and
communication mechanisms allocated to each software component

4

Prescriptive Process Model

 Defines a distinct set of activities, actions, tasks, milestones,
and work products that are required to engineer high-quality
software
 The activities may be linear, incremental, or evolutionary

6

Waterfall Model
(Diagram)
Communication
Project initiation
Requirements
gathering
Planning
Estimating
Scheduling
Tracking Modeling
Analysis
Design Construction
Code
Test Deployment
Delivery
Support
Feedback
7

Waterfall Model
(Description)
 Oldest software lifecycle model and best understood by upper
management
 Used when requirements are well understood and risk is low
 Work flow is in a linear (i.e., sequential) fashion
 Used often with well-defined adaptations or enhancements to current
software

8

Waterfall Model
(Problems)
 Doesn't support iteration, so changes can cause confusion
 Difficult for customers to state all requirements explicitly and up front
 Requires customer patience because a working version of the
program doesn't occur until the final phase
 Problems can be somewhat alleviated in the model through the
addition of feedback loops (see the next slide)

9

Waterfall Model with
Feedback
(Diagram)
Communication
Project initiation
Requirements
gathering

Planning
Estimating
Scheduling
Tracking Modeling
Analysis
Design Construction
Code
Test Deployment
Delivery
Support
Feedback
10

Incremental Model
(Diagram)
Increment #1
Communication
Planning
Modeling
Construction
Deployment

Increment #2
Communication
Planning
Modeling
Construction
Deployment

Increment #3

Communication
Planning
Modeling
Construction
Deployment

11

Incremental Model
(Description)
 Used when requirements are well understood
 Multiple independent deliveries are identified
 Work flow is in a linear (i.e., sequential) fashion within an increment
and is staggered between increments
 Iterative in nature; focuses on an operational product with each
increment
 Provides a needed set of functionality sooner while delivering optional
components later
 Useful also when staffing is too short for a full-scale development

12

Prototyping Model
(Diagram)
Quick
Planning

Communication
Start

Modeling
Quick Design
Deployment,
Delivery,
and Feedback

Construction
Of Prototype
13

Prototyping Model
(Description)
 Follows an evolutionary and iterative approach
 Used when requirements are not well understood
 Serves as a mechanism for identifying software requirements
 Focuses on those aspects of the software that are visible to the
customer/user
 Feedback is used to refine the prototype

14

Prototyping Model
(Potential Problems)
 The customer sees a "working version" of the software, wants to stop
all development and then buy the prototype after a "few fixes" are
made
 Developers often make implementation compromises to get the
software running quickly (e.g., language choice, user interface,
operating system choice, inefficient algorithms)
 Solution:
 Define the rules up front on the final disposition of the prototype before it
is built
 In most circumstances, plan to discard the prototype and engineer the
actual production software with a goal toward quality

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THE RAD MODEL

60-90 Days
Team#3
Communication
Modeling
Planning Team#2
Modeling Construction
Team#1 Modeling
Construction

Construction

Deployement

RAD MODEL
(Description)
 Rapid application development (RAD) is an incremental process model
that emphasizes on extremely short development cycle (e.g., 60 to 90
days)
 …Provided requirements are well understood and project scope is
constrained. encompasses following phases:
 Communication:
 Works to understand the business problems.
 Planning:
 is essential because multiple software teams work in parallel on
different system functions.
 Modeling includes
 Business modeling-
 The information flow among business functions is modeled.

RAD MODEL
(Description)
 Data modeling-
 Previous information flow is refined into a set of data objects.
 Process modeling-
 The data objects defined in the data modeling phase are transformed to
implement a business function.
 Construction :
 RAD assumes the use of fourth generation techniques Rather
than conventional third generation programming languages.
 Reuse
 Automated tools are used for construction.
 Deployment :

RAD MODEL
(Drawbacks)
 For large but scalable projects, RAD requires sufficient human
resources to create the right number of RAD teams.
 RAD requires developers and customers who are committed to
rapid fire activities.
 Not all types of applications are appropriate for RAD.
 RAD is not appropriate when technical risks are high.

Spiral Model
(Diagram)
Planning

Communication

Start Modeling

Start

Deployment Construction

20

Spiral Model
(Description)
 Follows an evolutionary approach
 Used when requirements are not well understood and risks are high
 Inner spirals focus on identifying software requirements and project risks;
may also incorporate prototyping
 Outer spirals take on a classical waterfall approach after requirements
have been defined, but permit iterative growth of the software
 Operates as a risk-driven model…a go/no-go decision occurs after each
complete spiral in order to react to risk determinations
 Requires considerable expertise in risk assessment
 Serves as a realistic model for large-scale software development

21

General Weaknesses of
Evolutionary Process Models
1) Prototyping poses a problem to project planning because of the
uncertain number of iterations required to construct the product
2) Evolutionary software processes do not establish the maximum
speed of the evolution
• If too fast, the process will fall into chaos
• If too slow, productivity could be affected
3) Software processes should focus first on flexibility and
extensibility, and second on high quality
• We should prioritize the speed of the development over zero defects
• Extending the development in order to reach higher quality could
result in late delivery

22

Component-based Development
Model
 Consists of the following process steps
 Available component-based products are researched and evaluated
for the application domain in question
 Component integration issues are considered
 A software architecture is designed to accommodate the
components
 Components are integrated into the architecture
 Comprehensive testing is conducted to ensure proper functionality
 Relies on a robust component library
 Capitalizes on software reuse, which leads to documented
savings in project cost and time

24

Formal Methods Model
(Description)
 Encompasses a set of activities that leads to formal
mathematical specification of computer software
 Enables a software engineer to specify, develop, and verify a
computer-based system by applying a rigorous, mathematical
notation
 Ambiguity, incompleteness, and inconsistency can be
discovered and corrected more easily through mathematical
analysis
 Offers the promise of defect-free software
 Used often when building safety-critical systems

25

Formal Methods Model
(Challenges)
 Development of formal methods is currently quite time-
consuming and expensive
 Because few software developers have the necessary
background to apply formal methods, extensive training is
required
 It is difficult to use the models as a communication mechanism
for technically unsophisticated customers

26

Pressman ch-3-prescriptive-process-models

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