Software process

Software Processes

Loganathan R

Prof. Loganathan R., CSE, HKBKCE 1

Objectives
• Understand the concept of software process
models
• Understand three generic process models and
when they may be used
• Understand the activities involved in
requirements engineering, software
development, testing and evolution
• Understand the Rational Unified Process model
• Introduce the CASE technology to support
software process activities


The Software Process
• Common fundamental activities to all Software processes are:
– Specification;
– Design;
– Validation;
– Evolution.
• A software process model is an abstract representation of a
process. It presents a description of a process from some
particular perspective.


Generic software process models
• The waterfall model
– Separate and distinct phases of specification and development.
• Evolutionary(Iterative) development
– Specification, development and validation are interleaved.
• Component-Based Software Engineering
– The system is assembled from existing 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 implementable design.


Waterfall Model
Requirements
Definition

System and
Software Design

Implementation
and Unit Testing

Integration and
System Testing

Operation and
Maintenance

Waterfall Model phases
• Requirements analysis and definition
• Services, constraints & goals are established & Defined
• System and software design
• Establishes overall System architecture ,identifies & describes
the software system abstractions & their relationships
• Implementation and unit testing
• Design is realised as program units. Unit testing involves
verifying each unit meets its specification
• Integration and system testing
• Program unit are integrated and tested as a system to ensure it
meets the requirement specification.
• Operation and maintenance
• System is installed & put in use. Maintenance involves
correcting errors, improving implementation & enhancing with
new requirements as discovered


Waterfall model problems
• The main drawback of the waterfall model is the difficulty of
accommodating change after the process is underway. One
phase has to be complete before moving onto the next phase.
• Inflexible partitioning of the project into distinct stages makes
it difficult to respond to changing customer 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.

Evolutionary development
Concurrent
activities

Specification Initial
Version

Outline
Description
Development Intermediate
Versions

Final
Validation
Version


• Develop an initial implementation and expos to
user comment and then refine it through many
versions.
• Types:
• Exploratory development
– Objective is to work with customers and to evolve a final
system from an initial outline specification. Should start with
well-understood requirements and add new features as
proposed by the customer.
• Throw-away prototyping
– Objective is to understand the system requirements. Should
start with poorly understood requirements to clarify what is
really needed.


• Problems
– Lack of process visibility;
– Systems are often poorly structured;
– Special skills (e.g. in languages for rapid
prototyping) may be required.
• Applicability
– For small or medium-size interactive systems;
– For parts of large systems (e.g. the user interface);
– For short-lifetime systems.


Component-based software engineering

Requirements Component Requirements System Design
Specifications Analysis Modifications with Reuse

Development System
and Integration Validation


Component-based software engineering
• Based on systematic reuse where systems are integrated
from existing components or COTS (Commercial-off-the-
shelf) systems.
• Process stages
– Component analysis :- Search for components for given
specification
– Requirements modification :- Analyse the requirements using
the discovered component information and modify to reflect
the available components
– System design with reuse :- Framework of the system is
designed or existing framework is reused
– Development and integration :- non available components are
developed and integrated with COTS system to create the
required system
• This approach is becoming increasingly used as component
standards have emerged.

Process Iteration
• System requirements ALWAYS evolve in the
course of a project so, process iteration where
earlier stages are reworked is always part of
the process for large systems.
• Iteration can be applied to any of the generic
process models.
• Two (related) approaches
– Incremental delivery;
– Spiral development.


Incremental delivery

Define Outline Assign Requirements Design System
Requirements to Increments Architecture

Develop system Validate Integrate Validate
Increment Increment Increment System
Final
System
System Incomplete


• Rather than deliver the system as a single delivery, the
development (Specification, design & implementation)
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.


• 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.


Extreme programming
• Variant of incremental delivery.
• Based on the development based on the
development and delivery of very small
increments of functionality.
• Relies on constant code improvement, user
involvement in the development team and
pair wise programming.


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.

Spiral model of the software process
Deter mine objecti ves,
Evalua te alterna tives,
alterna tives and
identify , resolv e risks
constr aints Risk
analysis
Risk
anal ysis

Risk
Oper a-
anal ysis
Prototype 3 tional
Prototype 2 pr otoype
Risk
REVIEW anal ysis Proto-
type 1
Requir ements plan Simula tions , models , benchmarks
Life-cycle plan Concept of
Oper ation S/W
requir ements Product
design Detailed
Requir ement design
Development
plan validation Code
Unit test
Integ ration Design
V&V Integ ration
and test plan
Plan ne xt phase test
Acceptance
Service test Develop , verify
next-le vel pr oduct

Spiral model Sectors
• Objective setting
– Define the Specific objectives for that phase. Identify the
constraints on the process/product and project risk. Plan for
constraints & find alternate for risk or resolve.
• Risk assessment and reduction
– Risks are analysed & assessed and take steps to reduce the risks.
• Development and validation
– A development model for the system is chosen which can be any
of the generic models. Example for UI risk use evolutionary
prototyping, for safety risk use formal transformation, for sub-
system risk Waterfall model
• Planning
– The project is reviewed and the next phase of the spiral is planned.


Process activities
• 1. Software specification
• 2. Software design and implementation
• 3. Software validation
• 4. Software evolution


1. Software specification
• Software Specification or requirements engineering is the process of
understanding and defining what services are required and identifying
the constraints on the system’s operation and development.
• Requirements engineering process
– Feasibility study:- Estimate whether the current h/w & s/w technology will
satisfy user needs & cost-effective. Feasibility study should be cheap &quick.
– Requirements elicitation and analysis :- Derive the requirements by
observing existing system, discussing with users, task analysis & so on. Produce
system models & prototypes
– Requirements specification :- Translate the previous activity information
into requirements document. Types of requirements:
• User requirements :- for customer & end user
• System requirements : - detailed description of the required functionality
– Requirements validation :- Checks the requirements for realism consistency
& completeness.

The requirements engineering process

Requirements
Feasibility
Elicitation and
Study
Analysis
Requirements
Specification
Feasibility Requirements
Report Validation

System
Models
User and System
Requirements

Requirements
Document


2. Software Design and Implementation

• The process of converting the system
specification into an executable system.
• Software design
– is a description of software structure, data, interfaces
and algorithms used in the system that realises the
specification;
• Implementation
– Translate design structure into an executable
program;
• The activities of design and implementation are
closely related and may be inter-leaved.


The software design process

Requirement
Specification

Design activities

Architectural Abstract Interface Component Data Algorithm
Design Specificatio Design Design Structure Design
n Design

System Software Interface Component Data Algorithm
Architecture Specification Specification Specification Structure Specification
Specification

Design products


Software Design process activities
• Architectural design
Subsystem making up the system & their relationships are identified & documented

• Abstract specification
Abstract specification of subsystem services & its operating constraints are produced

• Interface design
Subsystem interfaces with other subsystem is designed unambiguously & documented

• Component design
Component services are allocated & its interfaces also designed
• Data structure design
The data structures used in the implementation is designed & specified
• Algorithm design
Algorithm to provide services are designed & specified


Design methods
• In Agile method, design process output is represented
in the code of the program
• The Structured methods produces graphical models
and code generated automatically from that. Includes
design process model, design notations, report formats
& design guidelines.
• Structured methods supports the following models:
– Object model :Shows object classes & their dependencies
– Sequence model :Shows how objects interact when system is
executing
– State transition model :Shows system states & triggers for
transition from one state to another
– Structural model :System Components & their aggregations
are documented
– Data-flow model :System is modelled using transformations
that takes place as it is processed

Programming and Debugging
• Translating a design into a program and
removing errors from that program.
• Programming is a personal activity - there is
no generic programming process.
• Programmers carry out some program testing
to discover faults in the program and remove
these faults in the debugging process.


The Debugging Process

Locate Design Error Repair Retest
Error Repair Error Program


3. Software validation
• Verification and validation (V & V) is 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 of the real data(customer data)
to be processed by the system.


The Testing Process

Component System Acceptance
Testing Testing Testing


Testing process stages
• Component or unit testing
– Individual components are tested independently
for correct operation;
– Components may be functions or objects or
coherent groupings of these entities.
• System testing
– Testing of the system as a whole to validate
functional & non-functional requirements. Testing
of emergent properties is particularly important.
• Acceptance testing
– Testing with customer data to check that the
system meets the customer’s needs &
performance.


Testing phases in a Software process
Requirements System System Detailed
Specification Specification Design Design

System Sub-system
Acceptance Module / Unit
Integration Integration
Test Plan Code and Test
Test Plan Test Plan

Acceptance System Sub-system
Service
Test Integration Test Integration Test

• Alpha testing : Acceptance testing
• Beta testing : For marketed products, involves delivering
system to potential customers who agree to use


4. Software evolution
• 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 demarcation
between development and evolution
(maintenance) this is increasingly irrelevant as
fewer and fewer systems are completely new.


System evolution

Define system Assess existing Propose system Modify
requirements systems changes systems

Existing New
systems system


The Rational Unified Process
• A modern process model derived from the work on
the UML and associated Unified Software
Development process.
• It is a Hybrid process model : Combines the elements
of generic process models, supports iteration &
illustrates good practices in specification & design
• Normally described from 3 perspectives
– A dynamic perspective that shows phases over time;
– A static perspective that shows process activities;
– A practice perspective that suggests good practice.


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.
Actors who interact with the system are identified and use cases are
Requirements
developed to model the system requirements.
A design model is created and documented using architectural models,
Analysis and design
component models, object models and sequence models.
The components in the system are implemented and structured into
Implementation implementation sub-systems. Automatic code generation from design
models helps accelerate this process.
Testing is an iterative process that is carried out in conjunction with
Test implementation. System testing follows the completion of the
implementation.
A product release is created, distributed to users and installed in their
Deployment
workplace.
Configuration and
This supporting workflow managed changes to the system
Change management
Project management This supporting workflow manages the system development
This workflow is concerned with making appropriate software tools
Environment
available to the software development team.

Computer-aided software engineering

• Computer-aided software engineering (CASE) is software to
support software development and evolution processes.
• Activity automation
– Graphical editors for system model development;
– Data dictionary to manage design entities;
– Graphical UI builder for user interface construction;
– Debuggers to support program fault finding;
– Automated translators to generate new versions of a program.


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.


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
Cross reference generators, static analysers, dynamic
Program analysis tools
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
Re-engineering tools
Testing tools
Debugging tools
Program analysis tools
Language-processing tools

Method support tools
Prototyping tools
Configuration management
tools
Change management tools
Documentation tools
Editing tools
Planning tools

Specification Design Implementation Verification &
Prof. Loganathan R., CSE, HKBKCE
Validation 45

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
Case
Technology

Tools Workbenches Environments

Integrated Process-centred
Editors Compilers File Comparators
Environments Environments

Analysis and
Programming Testing
Design

Multi-method Single-method General-purpose Language-specific
Workbenches Workbenches Workbenches Workbenches

Software process

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