dr izzat m alsmadi edited from ©ian sommerville & others software engineering, chapter 2 slide...

Dr Izzat M Alsmadi Edited from ©Ian Sommerville & others Software Engineering, Chapter 2 Slide 1

Software Processes(Chapter 4 from the textbook)


Objectives

To introduce software process models To describe Some generic process models

and when they may be used To describe outline process models for

requirements engineering, software development, testing and evolution

To explain the Rational Unified Process model

To introduce CASE technology to support software process activities


Topics covered

Software process models Process iteration Process activities The Rational Unified Process Computer-aided software engineering Agile development methods and processes.


The software process

A structured set of activities required to develop a software system. Major activities or stages include: Requirements, Design, Implementation, Testing, and Deployment.

Each stage of those listed may have one or more sub stages. For example, Requirement may include: communication, elicitation, specification, and verification. Design may include architectural and detail design.

In some projects, a stage maybe shortened, but it can never be ignored.


Framework Activities; different terminologies

In different books or references, some of those processes may be mixed, combined, or have different names.

Communication Planning Modeling (Design and specs)

• Analysis of requirements• Design

Construction (Implementation and testing)• Code generation• Testing

Deployment


Umbrella Activities

Those are considered as – secondary processes. Some projects may or may not include them.

Software project management Formal technical reviews Software quality assurance Software configuration management Work product preparation and production Reusability management Measurement Risk management


Generic software process models The waterfall model : Separate and distinct phases of

specification and development. Does not go to the next phase until completing the current phase.

Evolutionary development ( Prototyping).•Specification, development and validation are interleaved.

Develop “prototypes” for customers to see and verify. Component-based software engineering

•The system is assembled from existing components off-shelf components.

There are many variants of these models e.g. formal development where a waterfall-like process is used but the specification is a formal specification that is refined through several stages to an implement-able design.


The Waterfall Model

Communication Planning

ModelingConstruction

Deployment analysis design code

test

project initiation requirement gathering estimating

scheduling tracking

delivery support feedback

We don’t go back to a stage once it is completed, and “usually” we don’t start a stage until the previous stage is completed.


Waterfall model phases Requirements analysis and definition System and software design Implementation and unit testing – developers tasks. Integration and system testing- testers tasks. Operation and maintenance. Customer support and

Customer service tasks. We use the waterfall model when we have fixed,

stable and known requirements. The main drawback of the waterfall model is the

difficulty of accommodating changes after the process is underway. One phase has to be completed before moving to the next phase.


Waterfall model problems

Inflexible partitioning of the project into distinct stages makes it difficult to respond to changing customer requirements (not suitable for unstable requirements).

Therefore, this model is only appropriate when the requirements are well-understood and changes will be fairly limited during the design process.

Few business systems have stable requirements. The waterfall model is mostly used for large systems

engineering projects where a system is developed at several sites. (such as space or govt projects).


Evolutionary development We want the software to “evolve” to its final form

“requirements are not completely known, or we need to verify them with the customers.

Exploratory development : The Objective is to work with customers and to evolve a final system from an initial outline specification.• We should start with those requirements that are well-understood and agreed upon and then add new features as proposed by the customer.

Throw-away prototyping : The objective is to understand the system requirements.

We may start with poorly understood requirements, then build prototypes to clarify what is really needed.


Evolutionary Models: Prototyping

Communication

Quick plan

Construction of prototype

Modeling Quick design

Delivery & Feedback

Deployment

communication

Quickplan

ModelingQuick design

Constructionof prototype

Deploymentdelivery &feedback


Evolutionary development

Problems• Lack of process visibility ( We don’t have the complete

requirements and hence we are not sure how much resources we may need, or of the project will be a successful one);

• Systems are often poorly structured (because they evolve and change continuously);

• Special skills (e.g. in languages for rapid prototyping) may be required.


Evolutionary development

Applicability• For small or medium-size interactive systems;• For parts of large systems (e.g. the user

interface);• For short-lifetime systems.• Prototyping can be used in initial stages as a

way of collecting requirements. (Customers may find it easier to make comments on actual product and not just papers or documents).


Process iteration

System requirements ALWAYS evolve in the course of a project. As a result, process iteration where earlier stages are reworked is always part of large systems’ processes. (MS Windows & Office continuously have updates, newer versions, batches and bug fixes).

Iteration can be applied to any of the generic process models.

Two (related) approaches• Incremental delivery;• Spiral development.


Incremental delivery

Rather than delivering the system as a single delivery, the development and delivery is broken down into increments with each increment delivering part of the required functionality.

User requirements are prioritised and the highest priority requirements are included in early increments.

Once the development of an increment is started, the requirements are frozen though requirements for later increments can continue to evolve.


The Incremental Model

C o m m u n i c a t i o n

P l a n n i n g

M o d e l i n g

C o n s t r u c t i o n

D e p l o y m e n t

d e l i v e ry f e e d b a c k

analys is

des ign code

t es t

increment # 1

increment # 2

delivery of 1st increment

delivery of 2nd increment

delivery of nth increment

increment # n

project calendar time

C o m m u n i c a t i o nP l a n n i n g

M o d e l i n g


D e p l o y m e n t

d e l i v e r y

f e e d b a c k

analys is

des ign code

t es t

C o m m u n i c a t i o nP l a n n i n g

M o d e l i n g


D e p l o y m e n t

d e l i v e r y

f e e d b a c k

analys is

des igncode t es t


Incremental development advantages

Customer value can be delivered with each increment so system functionality is available earlier.

Early increments act as a prototype to help elicit requirements for later increments.

Lower risk of overall project failure. The highest priority system services tend to

receive the most testing.


Spiral development

Process is represented as a spiral rather than as a sequence of activities with backtracking.

Each loop in the spiral represents a phase in the process.

No fixed phases such as specification or design - loops in the spiral are chosen depending on what is required.

Risks are explicitly assessed and resolved throughout the process. (This is the main difference from the Incremental model).


Spiral model of the software process

Riskanalysis

Riskanalysis

Riskanalysis

Riskanalysis Proto-

type 1

Prototype 2

Prototype 3Opera-tionalprotoype

Concept ofOperation

Simulations, models, benchmarks

S/Wrequirements

Requirementvalidation

DesignV&V

Productdesign Detailed

design

Code

Unit test

IntegrationtestAcceptance

testService Develop, verifynext-level product

Evaluate alternatives,identify, resolve risks

Determine objectives,alternatives and

constraints

Plan next phase

Integrationand test plan

Developmentplan

Requirements planLife-cycle plan

REVIEW


Evolutionary Models: The Spiral

communication

planning

modeling

constructiondeployment delivery feedback

start

analysis design

code test

estimation scheduling risk analysis


Spiral model sectors

Objective setting• Specific objectives for the phase are identified.

Risk assessment and reduction• Risks are assessed and activities put in place to

reduce the key risks. Development and validation

• A development model for the system is chosen which can be any of the generic models.

Planning• The project is reviewed and the next phase of the

spiral is planned.


General process activities

Software specification Software design and implementation Software validation Software evolution


Software specification

The process of establishing what services are required and the constraints on the system’s operation and development.

Requirements engineering process• Feasibility study;• Requirements elicitation and analysis;• Requirements specification;• Requirements validation.


The requirements engineering process

Feasibilitystudy

Requirementselicitation and

analysisRequirementsspecification

Requirementsvalidation

Feasibilityreport

Systemmodels

User and systemrequirements

Requirementsdocument


Software design and implementation

Software design : To design a software structure or model that realises the specification; The design is the link between the requirements and the code (The blueprint such as the one used in buildings).

Implementation : The process of converting the system specification into an executable system (i.e. the code or the software).

The activities of design and implementation are closely related and may be inter-leaved.


Design process activities

Architectural design Abstract specification Interface design Component or detail design Data structure design Algorithm design


The software design process

Architecturaldesign

Abstractspecification

Interfacedesign

Componentdesign

Datastructuredesign

Algorithmdesign

Systemarchitecture

Softwarespecification

Interfacespecification

Componentspecification

Datastructure

specification

Algorithmspecification

Requirementsspecification

Design activities

Design products


Programming and debugging

Translating a design into a program and removing errors from that program.

We use programming or developing to refer to the implementation stage.

Programming is a personal activity - there is no generic programming process, but there are coding standards (such as naming conventions).

Programmers carry out some program testing to discover faults in the program and remove these faults in the debugging process (i.e. unit testing).


The debugging process

Locateerror

Designerror repair

Repairerror

Re-testprogram


Software validation

Verification and validation (V & V) are intended to show that a system conforms to its specification and meets the requirements of the system customer.

Involves checking and review processes and system testing.

System testing involves executing the system with test cases that are derived from the specification in order to be processed by the system.

Validation and verification occurs in the requirement stage while testing occurs within or after the implementation stage.


Testing stages

Component or unit testing : Individual components are tested independently; • Components may be functions or objects or

coherent groupings of these entities. Usually done by developers.

System testing: Testing of the system as a whole. Testing of emergent properties is particularly important. Usually done by local company testers.

Acceptance testing: Testing with customer data to check that the system meets the customer’s needs. Usually done by customers or independent testers.


The testing process

Componenttesting

Systemtesting

Acceptancetesting


Testing phases

Requirementsspecification

Systemspecification

Systemdesign

Detaileddesign

Module andunit codeand test

Sub-systemintegrationtest plan

Systemintegrationtest plan

Acceptancetest plan

ServiceAcceptance

testSystem

integration testSub-system

integration test


Other types of testing

Unit or white box testing (i.e. component testing). Black box testing (can be part of system testing). Integration testing (related to system testing). User Interface testing (can be part of system

testing). Alpha and Beta testing (can be part of

acceptance testing).


Software evolution or maintenance

Software is inherently flexible and can change. As requirements change, through changing

business circumstances, the software that supports the business must also evolve and change.

Although there has been a mixing between development and evolution (maintenance) this is increasingly irrelevant as fewer and fewer systems are completely new.


System evolution

Assess existingsystems

Define systemrequirements

Propose systemchanges

Modifysystems

Newsystem

Existingsystems


The Rational Unified Process

A modern process model derived from the work on the UML and associated process.

Normally described from 3 perspectives• A dynamic perspective that shows phases over

time;• A static perspective that shows process

activities;• A proactive perspective that suggests good

practices.


RUP phase model

Phase iteration

Inception Elaboration Construction Transition


RUP phases

Inception• Establish the business case for the system.

Elaboration• Develop an understanding of the problem

domain and the system architecture. Construction

• System design, programming and testing. Transition

• Deploy the system in its operating environment.


RUP good practice

Develop software iteratively Manage requirements Use component-based architectures Visually model software Verify software quality Control changes to software


Static workflows

Workflow Description

Business modelling The business processes are modelled using business use cases.

Requirements Actors who interact with the system are identified and use cases aredeveloped to model the system requirements.

Analysis and design A design model is created and documented using architecturalmodels, component models, object models and sequence models.

Implementation The components in the system are implemented and structured intoimplementation sub-systems. Automatic code generation from designmodels helps accelerate this process.

Test Testing is an iterative process that is carried out in conjunction withimplementation. System testing follows the completion of theimplementation.

Deployment A product release is created, distributed to users and installed in theirworkplace.

Configuration andchange management

This supporting workflow managed changes to the system (seeChapter 29).

Project management This supporting workflow manages the system development (seeChapter 5).

Environment This workflow is concerned with making appropriate software toolsavailable to the software development team.


Computer-aided software engineering CASE

Computer-aided software engineering (CASE) is a software to support software development and evolution processes (Example, .NET IDE).

Activity automation• Graphical editors for system model development (such as

UML, .NET, Eclipse, etc);• Data dictionary to manage design entities (OO design

tools);• Graphical UI builder for user interface construction (.NET,

Eclipse, etc.);• Debuggers to support program fault finding;• Automated translators to generate new versions of a

program (such as Installers).


CASE technology

CASE technology has led to significant improvements in the software process. However, these are not the order of magnitude improvements that were once predicted• Software engineering requires creative thought - this

is not readily automated;• Software engineering is a team activity and, for large

projects, much time is spent in team interactions. CASE technology does not really support these. (i.e. the personal activities, Some tools can be used to work as a communication media between project team members, project or defect tracking tools).


CASE classification

Classification helps us understand the different types of CASE tools and their support for process activities.

Functional perspective• Tools are classified according to their specific function.

Process perspective• Tools are classified according to process activities that

are supported. Integration perspective

• Tools are classified according to their organisation into integrated units.


Functional tool classification

Tool type Examples

Planning tools PERT tools, estimation tools, spreadsheets

Editing tools Text editors, diagram editors, word processors

Change management tools Requirements traceability tools, change control systems

Configuration management tools Version management systems, system building tools

Prototyping tools Very high-level languages, user interface generators

Method-support tools Design editors, data dictionaries, code generators

Language-processing tools Compilers, interpreters

Program analysis tools Cross reference generators, static analysers, dynamic analysers

Testing tools Test data generators, file comparators

Debugging tools Interactive debugging systems

Documentation tools Page layout programs, image editors

Re-engineering tools Cross-reference systems, program re-structuring systems


Activity-based tool classification

Specification Design Implementation Verificationand

Validation

Re-engineering tools

Testing tools

Debugging tools

Program analysis tools

Language-processingtools

Method support tools

Prototyping tools

Configurationmanagement tools

Change management tools

Documentation tools

Editing tools

Planning tools


CASE integration

Tools• Support individual process tasks such as design

consistency checking, text editing, etc. Workbenches

• Support a process phase such as specification or design, Normally include a number of integrated tools.

Environments• Support all or a substantial part of an entire

software process. Normally include several integrated workbenches.


Tools, workbenches, environments

Single-methodworkbenches

General-purposeworkbenches

Multi-methodworkbenches

Language-specificworkbenches

Programming TestingAnalysis and

design

Integratedenvironments

Process-centredenvironments

Filecomparators

CompilersEditors

EnvironmentsWorkbenchesTools

CASEtechnology


The Manifesto for Agile Software Development

“We are uncovering better ways of developing software by doing it and helping others do it. Through this work we have come to value:

•Individuals and interactions over processes and tools •Working software over comprehensive documentation •Customer collaboration over contract negotiation •Responding to change over following a plan

That is, while there is value in the items on the right, we value the items on the left more.”

Kent Beck et alKent Beck et al


What is “Agility”?

Effective (rapid and adaptive) response to change

Effective communication among all stakeholders

Drawing the customer onto the team Organizing a team so that it is in control of

the work performed

Yielding … Rapid, incremental delivery of software


An Agile Process

Is driven by customer descriptions of what is required (scenarios)

Recognizes that plans are short-lived Develops software iteratively with a heavy

emphasis on construction activities Delivers multiple ‘software increments’ Adapts as changes occur


Extreme Programming (XP)

The most widely used agile process, originally proposed by Kent Beck

XP Planning• Begins with the creation of “user stories”• Agile team assesses each story and assigns a cost• Stories are grouped to for a deliverable increment• A commitment is made on delivery date• After the first increment “project velocity” is used to help

define subsequent delivery dates for other increments



XP Design• Follows the KIS principle• Encourage the use of CRC cards .• For difficult design problems, suggests the creation of “spike

solutions”—a design prototype• Encourages “refactoring”—an iterative refinement of the internal

program design XP Coding

• Recommends the construction of a unit test for a store before coding commences (Test driven development).

• Encourages “pair programming” XP Testing

• All unit tests are executed daily• “Acceptance tests” are defined by the customer and executed to

assess customer visible functionality



unit test continuous integration

acceptance testing

pair programming

Release

user stories values acceptance test criteria iteration plan

simple design CRC cards

spike solutions prototypes

refactoring

software incrementproject velocity computed


Scrum

Originally proposed by Schwaber and Beedle Scrum—distinguishing features

• Development work is partitioned into “packets”• Testing and documentation are on-going as the

product is constructed• Work occurs in “sprints” and is derived from a

“backlog” of existing requirements• Meetings are very short and sometimes conducted

without chairs• “demos” are delivered to the customer with the time-

box allocated


Scrum


Crystal

Proposed by Cockburn and Highsmith Crystal—distinguishing features

• Actually a family of process models that allow “maneuverability” based on problem characteristics

• Face-to-face communication is emphasized• Suggests the use of “reflection workshops” to

review the work habits of the team


Key points

Software processes are the activities involved in producing and evolving a software system.

Software process models are abstract representations of these processes.

General activities are specification, design and implementation, validation and evolution.

Generic process models describe the organisation of software processes. Examples include the waterfall model, evolutionary development and agile development.

Iterative process models describe the software process as a cycle of activities.


Key points

Requirements engineering is the process of developing a software specification.

Design and implementation processes transform the specification to an executable program.

Validation involves checking that the system meets to its specification and user needs.

Evolution is concerned with modifying the system after it is in use.

The Rational Unified Process is a generic process model that separates activities from phases.

CASE technology supports software process activities.


Key Points

Agile development methodologies are suggested to deal with the continuously evolving requirements and the need of company to deliver software in a reasonable time.

Agile development accept changes on requirements and deal with them continuously. They focus on the product rather than the documents. They focus on customer satisfaction rather than contracts.


Key Points

The 2 factors that affect the software process is the stability of the requirements and the flexibility to change requirements. We need to keep a balance between those 2 factors because instable requirements causes a lot of troubles for the project management, while inflexible project may have problems with customers and come up to a complete failure.

dr izzat m alsmadi edited from ©ian sommerville & others software engineering, chapter 2 slide...

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