Chapter 2 Modeling the Process and Life Cycle Shari L. Pfleeger Joanne M. Atlee 4 th Edition

Chapter 2

Modeling the Process and LifeCycle

Shari L. Pfleeger

Joanne M. Atlee

4th Edition

Pfleeger and Atlee, Software Engineering: Theory and Practice

Chapter 2.2

2.1 The Meaning of Process

• A process: a series of steps involving activities, constraints, and resources that produce an intended output of some kind

• A process involves a set of tools and techniques


Chapter 2.3

2.1 The Meaning of ProcessProcess Characteristics

• Prescribes all major process activities• Uses resources, subject to set of constraints (such as

schedule)• Produces intermediate and final products• May be composed of subprocesses with hierarchy or

links• Each process activity has entry and exit criteria• Activities are organized in sequence, so timing is

clear• Includes goals of each activity• Constraints may apply to an activity, resource or

product


Chapter 2.4

2.1 The Meaning of ProcessThe Importance of Processes

• Impose consistency and structure on a set of activities

• Guide us to understand, control, examine, and improve the activities

• Enable us to capture our experiences and pass them along


Chapter 2.5

2.2 Software Process ModelsReasons for Modeling a Process

• To form a common understanding• To find inconsistencies, redundancies,

omissions• To find and evaluate appropriate activities

for reaching process goals• To tailor a general process for a particular

situation in which it will be used


Chapter 2.6

2.2 Software Process ModelsSoftware Life Cycle

• When a process involves building a software, the process may be referred to as software life cycle– Requirements analysis and definition– System (architecture) design– Program (detailed/procedural) design– Writing programs (coding/implementation)– Testing: unit, integration, system– System delivery (deployment)

– Maintenance


Chapter 2.7

2.2 Software Process ModelsSoftware Development Process Models

• Waterfall model• V model• Prototyping model• Phased development: increments and

iteration• Spiral model• Agile methods


Chapter 2.8

2.2 Software Process ModelsWaterfall Model

• One of the first process development models proposed

• Works for well understood problems with minimal or no changes in the requirements

• Simple and easy to explain to customers• It presents

– a very high-level view of the development process– sequence of process activities

• Each major phase is marked by milestones and deliverables (artifacts)


Chapter 2.9

2.2 Software Process ModelsWaterfall Model (continued)


Chapter 2.10

2.2 Software Process ModelsDrawbacks of The Waterfall Model

• Views software development as manufacturing process

• No guidance how to handle changes to products and activities during development

• There is no iteration• The clients may not know the requirements• Changing requirements in later stages cause

increased overall project cost• Long wait before a final product


Chapter 2.11

2.2 Software Process ModelsV Model

• A variation of the waterfall model• Uses unit testing to verify module design• Uses integration testing to verify system design• Uses acceptance testing to validate the

requirements• If problems are found during verification and

validation, the left side of the V can be re-executed before testing on the right side is re-enacted

• Adoption by medical device industry


Chapter 2.12

2.2 Software Process ModelsV Model (continued)


Chapter 2.13

2.2 Software Process ModelsDrawbacks of The V Model

• Has similar drawbacks as the waterfall model• Too simple - may not reflect the software

process accurately• Use of inefficient and ineffective testing

techniques• Rigid link between left-side and right-side

(acceptance testing corresponds to the user requirements)


Chapter 2.14

2.2 Software Process ModelsPrototyping Model

• Reduces risk and uncertainty in the development as well as time and cost

• Online systems and HCI


Chapter 2.15

2.2 Software Process ModelsDrawbacks of The Prototype Model

• Not sufficient analysis (functionality, scalability, maintainability)

• User misunderstanding (prototype vs. final product)

• Developer misunderstanding the user reqs.• Too much time spent on prototype

development – Increased cost– Increased involvement and attachment to

prototype


Chapter 2.16

2.2 Software Process ModelsPhased Development: Increments and Iterations

• Shorter cycle time• System delivered in pieces

– enables customers to have some functionality while the rest is being developed

• Allows two systems functioning in parallel– the production system (release n): currently

being used– the development system (release n+1): the next

version

• Supported by US DoD, NASA


Chapter 2.17

2.2 Software Process ModelsPhased Development: Increments and Iterations(continued)


Chapter 2.18


• Incremental development: starts with small functional subsystem and adds functionality with each new release

• Iterative development: starts with full system, then changes functionality of each subsystem with each new release


Chapter 2.19


• Phased development is desirable for several reasons– Markets can be created early for functionality that

has never before been offered– The development team can focus on different

areas of expertise with different releases– Easier to test and debug– Regression testing after each iteration


Chapter 2.20

2.2 Software Process ModelsSpiral Model

• Suggested by Boehm (1988)• Combines development activities with risk

management to minimize and control risks• The model is presented as a spiral in which

each iteration is represented by a circuit around four major activities– Plan– Determine goals, alternatives and constraints– Evaluate alternatives and risks– Develop and test


Chapter 2.21

2.2 Software Process ModelsSpiral Model (continued)


Chapter 2.22

2.2 Software Process ModelsAgile Methods

• Emphasis on flexibility in producing software quickly and capably

• Agile manifesto– Value individuals and interactions over process

and tools– Prefer to invest time in producing working software

rather than in producing comprehensive documentation

– Focus on customer collaboration rather than contract negotiation

– Concentrate on responding to change rather than on creating a plan and then following it


Chapter 2.23

2.2 Software Process ModelsAgile Methods: Examples of Agile Process

• Extreme programming (XP)• Scrum: 30-day iterations; multiple self-

organizing teams; daily “scrum” coordination

• Adaptive software development (ASD)


Chapter 2.24

2.2 Software Process ModelsAgile Methods: Extreme Programming

• Emphasis on four charateristics of agility– Communication: continual interchange between

customers and developers– Simplicity: select the simplest design or

implementation– Courage: commitment to delivering functionality

early and often– Feedback: loops built into the various activitites

during the development process


Chapter 2.25

2.2 Software Process ModelsAgile Methods: Twelve Facets of XP

• Planning game (weekly meeting or per

iteration)

• Small release (weeks rather than months)

• Common vision• Simple design• Writing tests first• Refactoring

• Pair programming• Collective ownership• Continuous

integration (small increments)

• Sustainable pace (40 hours/week)

• On-site customer• Coding standard


Chapter 2.26

2.2 Software Process ModelsExtreme Programming

• Frequent releases in short development cycles to achieve higher quality and productivity

• Programming pairs, extensive code review, and unit testing

• Frequent communication with the customer and programmers


Chapter 2.27

2.2 Software Process ModelsSidebar 2.2 When Extreme is Too Extreme?

• XP's practices are interdependent – A vulnerability if one of them is modified

• Requirements expressed as a set of test cases must be passed by the software– System passes the tests but is not what the customer is

paying for

• Refactoring issue– Difficult to rework a system w/o degrading architecture

• User stories: scalability, vague, incomplete, non-functional requirements


Chapter 2.28

2.2 Software Process ModelsAgile Methods: Scrum

• 30-day iterations• multiple self-organizing teams• daily “scrum” coordination• three roles: product owner, development

team, and scrum master• sprint (iteration): basic unit in scrum


Chapter 2.29

• Notation depends on what we want to capture in the model

• The two major notation categories– Static model: depicts the process– Dynamic model: enacts the process

2.3 Tools and Techniques for Process Modeling


Chapter 2.30

• Element of a process are viewed in terms of seven types– Activity– Sequence– Process model– Resource– Control – Policy– Organization

• Several templates, such as an Artifact Definition Template

2.3 Tools and Techniques for Process ModelingStatic Modeling: Lai Notation


Chapter 2.31

Name Car Synopsis This is the artifact that represents a class of cars. Complexity type Composite Data type (car_c, user-defined) Artifact-state list parked ((state_of(car.engine) = off)

(state_of(car.gear) = park) (state_of(car.speed) = stand))

Car is not moving, and engine is not running.

initiated ((state_of(car.engine) = on) (state_of(car.key_hole) = has-key) (state_of(car-driver(car.)) = in-car) (state_of(car.gear) = drive) (state_of(car.speed) = stand))

Car is not moving, but the engine is running

moving ((state_of(car.engine) = on) (state_of(car.keyhole) = has-key) (state_of(car-driver(car.)) = driving) ((state_of(car.gear) = drive) or (state_of(car.gear) = reverse)) ((state_of(car.speed) = stand) or (state_of(car.speed) = slow) or (state_of(car.speed) = medium) or (state_of(car.speed) = high))

Car is moving forward or backward.

Sub-artifact list doors The four doors of a car. engine The engine of a car. keyhole The ignition keyhole of a

car. gear The gear of a car. speed The speed of a car. Relations list car-key This is the relation between a car and a key. car-driver This is the relation between a car and a driver.

2.3 Tools and Techniques for Process ModelingStatic Modeling: Lai Notation


Chapter 2.32

2.3 Tools and Techniques for Process ModelingStatic Modeling: Lai Notation (continued)

• The process of starting a car


Chapter 2.33

2.3 Tools and Techniques for Process ModelingStatic Modeling: Lai Notation (continued)

• Transition diagram illustrates the transition for a car


Chapter 2.34

• Enables enaction of process to see what happens to resources and artifacts as activities occur

• Simulate alternatives and make changes to improve the process

• Example: systems dynamics model

2.3 Tools and Techniques for Process ModelingDynamic Modeling


Chapter 2.35

2.3 Tools and Techniques for Process ModelingDynamic Modeling: System Dynamics (continued)• Pictorial presentation of factors affecting

productivity• Arrows indicate how changes in one factor change

another


Chapter 2.36

2.5. Information System ExamplePiccadilly Television Advertising System

• Needs a system that is easily maintained and changed

• Requirements may change– Waterfall model is not applicable

• User interface prototyping is an advantage• There is uncertainty in regulation and

business constraints– Need to manage risks

• Spiral model is the most appropriate


Chapter 2.37

2.5. Information System ExamplePiccadilly System (continued)

• Risk can be viewed in terms of two facets– Probability: the likelyhood a particular problem

may occur– Severity: the impact it will have on the system

• To manage risk, it needs to include characterization of risks in the process model– Risk is an artifact that needs to be described


Chapter 2.38

2.5. Information System ExampleLai Artifact Table for Piccadilly System

Name Risk (problemX) Synopsis This is the artifact that represents the risk that problem X

will occur and have a negative affect on some aspect of the development process.

Complexity type Composite Data type (risk_s, user_defined) Artifact-state list low ((state_of(probability.x) = low)

(state_of(severity.x) = small)) Probability of problem is low, severity problem impact is small.

high-medium ((state_of(probability.x) = low) (state_of(severity.x) = large))

Probability of problem is low, severity problem impact is large.

low-medium ((state_of(probability.x) = high) (state_of(severity.x) = small))

Probability of problem is high, severity problem impact is small.

high ((state_of(probability.x) = high) (state_of(severity.x) = large))

Probability of problem is high, severity problem impact is large.

Sub-artifact list probability.x The probability that

problem X will occur. severity.x The severity of the

impact should problem X occur on the project.


Chapter 2.39

2.6 Real Time ExampleAriane-5 Software

• Involved reuse of software from Ariane-4• The reuse process model

– Identify resuable subprocesses, describe them and place them in a library

– Examine the requirements for the new software and the reusable components from library and produce revised set of requirements

– Use the revised requirements to design the software

– Evaluate all reused design components to certify the correctness and consistency

– Build or change the software


Chapter 2.40

2.6 Real Time ExampleAriane-5 Software (continued)

• Reuse process model presentation


Chapter 2.41

2.7 What this Chapter Means for You

• Process development involves activities, resources, and product

• Process model includes organizational, functional, behavioral and other prespectives

• A process model is useful for guiding team behavior, coordination and collaboration

Documents

Chapter 2 Modeling the Process and Life Cycle Shari L. Pfleeger Joanne M. Atlee 4 th Edition