Unit3 Software Process
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Software Processes
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 1
Objectives ● ●
●
● ●
To introduce software process models To describe three 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
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 2
Topics covered ● ● ● ● ●
Software process models Process iteration Process activities The Rational Unified Process Computer-aided software engineering
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 3
The software process ●
A structured set of activities required to develop a software system • • • •
●
Specification –Functionality of the software and constraints on its operation must be defined; Design and implementation- The software to meet the specification must be produced; Validation- Must be validated to ensure that it does what the customer wants ; Evolution –The software must evolve to meet changing customers need.
A software process model is an abstract representation of a process. It presents a description of a process from some particular perspective and thus provides only partial information about that process.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 4
Generic software process models ●
The waterfall model •
●
Evolutionary development •
●
Specification, development and validation are interleaved.
Component-based software engineering •
●
Separate and distinct phases of specification and development.
The system is assembled from existing components.
There are many variants of these models .They are not mutually exclusive and are often used together 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.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 5
Waterfall model Requirements definition System and software design Implementation and unit testing Integration and system testing Operation and maintenance
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 6
Waterfall model phases ●
●
● ● ● ●
Requirements analysis and definition-The system’s services,constraints and goals are established by consultation with system users. System and software design- The system design process partitions the requirements to either hardware or software systems.It establishes an overall system architecture.Software design involves identifying and describing the fundamental software system abstractions and their relationships. Implementation and unit testing Integration and system testing Operation and maintenance 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.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 7
Waterfall model problems ●
●
● ●
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.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 8
Evolutionary development ●
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.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 9
Evolutionary development Concurrent activities
Specification
Outline description
Development
Validation
©Ian Sommerville 2004
Software Engineering, 7th edition.
Initial version
Intermediate versions
Final version
Slide 10
Evolutionary development ●
Problems • • •
●
Lack of process visibility-need regular deliverables to measure progress,it is not cost –effective to produce documents that reflect every version of the system; Systems are often poorly structured- Continual change tends to corrupt the software structure; 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.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 11
Component-based software engineering (CBSE) ●
●
●
Based on systematic reuse where systems are integrated from existing components or COTS (Commercial-off-theshelf) systems. Process stages • Component analysis -Given the requirements specification, a search is made for components to implement that specification; • Requirements modification – The requirements are analysed using information about the components that have been discovered and modify to reflect the available components; • System design with reuse- The framework of the system is designed or an existing framework is reused; • Development and integration- System that cannot be externally obtained is developed.
This approach is becoming increasingly used as component standards have emerged.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 12
Reuse-oriented development
Requirements specification
Component analysis
Requirements modification
System design with reuse
Development and integ ration
©Ian Sommerville 2004
Software Engineering, 7th edition.
System validation
Slide 13
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.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 14
Incremental delivery ●
●
●
Rather than deliver 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.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 15
Incremental development
Define outline requirements
Develop system increment
Assign requirements to increments
Validate increment
Design system architecture
Integrate increment
Validate system Final system
System incomplete
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 16
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.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 17
Spiral development ●
●
● ●
●
●
The spiral model of the software was originally proposed by Boehm. 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. The main difference between the spiral model and other software process models is the explicit recognition of risk in the spiral model
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 18
Spiral model of the software process Deter mine objecti ves, alternatives and constraints
Evaluate alternatives, identify, resolve risks
Risk analysis Risk analysis Risk analysis
REVIEW Requir ements plan Life-cycle plan
Plan ne xt phase
©Ian Sommerville 2004
Oper ational protoype
Prototype 3
Prototype 2 Risk analysis Prototype 1
Simulations, models, benchmar ks Concept of Oper ation
S/W requir ements
Development plan
Requir ement validation
Integration and test plan
Design V&V Acceptance test Service
Product design
Detailed design Code
Unit test Integration test
Software Engineering, 7th edition.
Develop , verify next-level pr oduct
Slide 19
Spiral model sectors ●
Objective setting •
●
Risk assessment and reduction •
●
Risks are assessed and activities put in place to reduce the key risks.
Development and validation •
●
Specific objectives for the phase are identified.
After risk evaluation,a development model for the system is chosen which can be any of the generic models.
Planning •
The project is reviewed and a decision made whether to continue with a further loop of the spiral,If it is decided to continue, the next phase of the project is planned.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 20
Process activities ● ● ● ●
Software specification Software design and implementation Software validation Software evolution
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 21
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.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 22
The requirements engineering process Feasibility study
Requirements elicitation and analysis Requirements specification Requirements validation
Feasibility report System models User and system requirements
Requirements document
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 23
Software design and implementation ●
●
The process of converting the system specification into an executable system. Software design •
●
Implementation •
●
Design a software structure that realises the specification; Translate this structure into an executable program;
The activities of design and implementation are closely related and may be inter-leaved.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 24
Design process activities ● ● ● ● ● ●
Architectural design Abstract specification Interface design Component design Data structure design Algorithm design
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 25
The software design process
Requirements specifica tion Design acti vities Architectur al design
Abstract specifica tion
Interface design
Component design
Data structur e design
Algorithm design
System architectur e
Software specifica tion
Interface specifica tion
Component specifica tion
Data structur e specifica tion
Algorithm specifica tion
Design pr oducts
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 26
Structured methods ●
●
●
Systematic approaches to developing a software design. The design is usually documented as a set of graphical models. Possible models • • • • •
Object model; Sequence model; State transition model; Structural model; Data-flow model.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 27
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.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 28
The debugging process
Locate error
©Ian Sommerville 2004
Design error repair
Repair error
Software Engineering, 7th edition.
Re-test program
Slide 29
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 to be processed by the system.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 30
The testing process
Component testing
©Ian Sommerville 2004
System testing
Software Engineering, 7th edition.
Acceptance testing
Slide 31
Testing stages ●
Component or unit testing • •
●
System testing •
●
Individual components are tested independently; Components may be functions or objects or coherent groupings of these entities. Testing of the system as a whole. Testing of emergent properties is particularly important.
Acceptance testing •
Testing with customer data to check that the system meets the customer’s needs.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 32
Testing phases
Requirements specification
System specification
System integration test plan
Acceptance test plan
Service
System design
Acceptance test
©Ian Sommerville 2004
Detailed design
Sub-system integration test plan
System integration test
Module and unit code and test
Sub-system integration test
Software Engineering, 7th edition.
Slide 33
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.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 34
System evolution
Define system requirements
Assess existing systems
Propose system changes
Existing systems
©Ian Sommerville 2004
Modify systems
New system
Software Engineering, 7th edition.
Slide 35
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 practive perspective that suggests good practice.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 36
RUP phase model
Phase iteration
Inception
Elaboration
©Ian Sommerville 2004
Construction
Software Engineering, 7th edition.
Transition
Slide 37
RUP phases ●
Inception •
●
Elaboration •
●
Develop an understanding of the problem domain and the system architecture.
Construction •
●
Establish the business case for the system.
System design, programming and testing.
Transition •
Deploy the system in its operating environment.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 38
RUP good practice ● ● ● ● ● ●
Develop software iteratively Manage requirements Use component-based architectures Visually model software Verify software quality Control changes to software
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 39
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 are developed to model the system requirements.
Analysis and design
A design model is created and documented using architectural models, component models, object models and sequence models.
Implementation
The components in the system are implemented and structured into implementation sub-systems. Automatic code generation from design models helps accelerate this process.
Test
Testing is an iterative process that is carried out in conjunction with implementation. System testing follows the completion of the implementation.
Deployment
A product release is created, distributed to users and installed in their workplace.
Configuration and change management
This supporting workflow managed changes to the system (see Chapter 29).
Project management
This supporting workflow manages the system development (see Chapter 5).
Environment
This workflow is concerned with making appropriate software tools available to the software development team.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 40
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.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 41
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.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 42
CASE classification ●
●
Classification helps us understand the different types of CASE tools and their support for process activities. Functional perspective •
●
Process perspective •
●
Tools are classified according to their specific function. Tools are classified according to process activities that are supported.
Integration perspective •
Tools are classified according to their organisation into integrated units.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 43
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
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 44
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
©Ian Sommerville 2004
Design
Implementation
Verification and Validation
Software Engineering, 7th edition.
Slide 45
CASE integration ●
Tools •
●
Workbenches •
●
Support individual process tasks such as design consistency checking, text editing, etc. 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.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 46
Tools, workbenches, environments CASE technology
Workbenches
Tools
Editors
Compilers
File comparators
Analysis and design
Multi-method workbenches
©Ian Sommerville 2004
Integrated environments
Programming
Single-method workbenches
Environments
Process-centred environments
Testing
General-purpose workbenches
Software Engineering, 7th edition.
Language-specific workbenches
Slide 47
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 componentbased software engineering. Iterative process models describe the software process as a cycle of activities.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 48
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.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 49
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 1
Objectives ● ●
●
● ●
To introduce software process models To describe three 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
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 2
Topics covered ● ● ● ● ●
Software process models Process iteration Process activities The Rational Unified Process Computer-aided software engineering
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 3
The software process ●
A structured set of activities required to develop a software system • • • •
●
Specification –Functionality of the software and constraints on its operation must be defined; Design and implementation- The software to meet the specification must be produced; Validation- Must be validated to ensure that it does what the customer wants ; Evolution –The software must evolve to meet changing customers need.
A software process model is an abstract representation of a process. It presents a description of a process from some particular perspective and thus provides only partial information about that process.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 4
Generic software process models ●
The waterfall model •
●
Evolutionary development •
●
Specification, development and validation are interleaved.
Component-based software engineering •
●
Separate and distinct phases of specification and development.
The system is assembled from existing components.
There are many variants of these models .They are not mutually exclusive and are often used together 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.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 5
Waterfall model Requirements definition System and software design Implementation and unit testing Integration and system testing Operation and maintenance
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 6
Waterfall model phases ●
●
● ● ● ●
Requirements analysis and definition-The system’s services,constraints and goals are established by consultation with system users. System and software design- The system design process partitions the requirements to either hardware or software systems.It establishes an overall system architecture.Software design involves identifying and describing the fundamental software system abstractions and their relationships. Implementation and unit testing Integration and system testing Operation and maintenance 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.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 7
Waterfall model problems ●
●
● ●
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.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 8
Evolutionary development ●
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.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 9
Evolutionary development Concurrent activities
Specification
Outline description
Development
Validation
©Ian Sommerville 2004
Software Engineering, 7th edition.
Initial version
Intermediate versions
Final version
Slide 10
Evolutionary development ●
Problems • • •
●
Lack of process visibility-need regular deliverables to measure progress,it is not cost –effective to produce documents that reflect every version of the system; Systems are often poorly structured- Continual change tends to corrupt the software structure; 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.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 11
Component-based software engineering (CBSE) ●
●
●
Based on systematic reuse where systems are integrated from existing components or COTS (Commercial-off-theshelf) systems. Process stages • Component analysis -Given the requirements specification, a search is made for components to implement that specification; • Requirements modification – The requirements are analysed using information about the components that have been discovered and modify to reflect the available components; • System design with reuse- The framework of the system is designed or an existing framework is reused; • Development and integration- System that cannot be externally obtained is developed.
This approach is becoming increasingly used as component standards have emerged.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 12
Reuse-oriented development
Requirements specification
Component analysis
Requirements modification
System design with reuse
Development and integ ration
©Ian Sommerville 2004
Software Engineering, 7th edition.
System validation
Slide 13
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.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 14
Incremental delivery ●
●
●
Rather than deliver 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.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 15
Incremental development
Define outline requirements
Develop system increment
Assign requirements to increments
Validate increment
Design system architecture
Integrate increment
Validate system Final system
System incomplete
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 16
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.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 17
Spiral development ●
●
● ●
●
●
The spiral model of the software was originally proposed by Boehm. 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. The main difference between the spiral model and other software process models is the explicit recognition of risk in the spiral model
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 18
Spiral model of the software process Deter mine objecti ves, alternatives and constraints
Evaluate alternatives, identify, resolve risks
Risk analysis Risk analysis Risk analysis
REVIEW Requir ements plan Life-cycle plan
Plan ne xt phase
©Ian Sommerville 2004
Oper ational protoype
Prototype 3
Prototype 2 Risk analysis Prototype 1
Simulations, models, benchmar ks Concept of Oper ation
S/W requir ements
Development plan
Requir ement validation
Integration and test plan
Design V&V Acceptance test Service
Product design
Detailed design Code
Unit test Integration test
Software Engineering, 7th edition.
Develop , verify next-level pr oduct
Slide 19
Spiral model sectors ●
Objective setting •
●
Risk assessment and reduction •
●
Risks are assessed and activities put in place to reduce the key risks.
Development and validation •
●
Specific objectives for the phase are identified.
After risk evaluation,a development model for the system is chosen which can be any of the generic models.
Planning •
The project is reviewed and a decision made whether to continue with a further loop of the spiral,If it is decided to continue, the next phase of the project is planned.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 20
Process activities ● ● ● ●
Software specification Software design and implementation Software validation Software evolution
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 21
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.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 22
The requirements engineering process Feasibility study
Requirements elicitation and analysis Requirements specification Requirements validation
Feasibility report System models User and system requirements
Requirements document
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 23
Software design and implementation ●
●
The process of converting the system specification into an executable system. Software design •
●
Implementation •
●
Design a software structure that realises the specification; Translate this structure into an executable program;
The activities of design and implementation are closely related and may be inter-leaved.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 24
Design process activities ● ● ● ● ● ●
Architectural design Abstract specification Interface design Component design Data structure design Algorithm design
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 25
The software design process
Requirements specifica tion Design acti vities Architectur al design
Abstract specifica tion
Interface design
Component design
Data structur e design
Algorithm design
System architectur e
Software specifica tion
Interface specifica tion
Component specifica tion
Data structur e specifica tion
Algorithm specifica tion
Design pr oducts
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 26
Structured methods ●
●
●
Systematic approaches to developing a software design. The design is usually documented as a set of graphical models. Possible models • • • • •
Object model; Sequence model; State transition model; Structural model; Data-flow model.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 27
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.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 28
The debugging process
Locate error
©Ian Sommerville 2004
Design error repair
Repair error
Software Engineering, 7th edition.
Re-test program
Slide 29
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 to be processed by the system.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 30
The testing process
Component testing
©Ian Sommerville 2004
System testing
Software Engineering, 7th edition.
Acceptance testing
Slide 31
Testing stages ●
Component or unit testing • •
●
System testing •
●
Individual components are tested independently; Components may be functions or objects or coherent groupings of these entities. Testing of the system as a whole. Testing of emergent properties is particularly important.
Acceptance testing •
Testing with customer data to check that the system meets the customer’s needs.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 32
Testing phases
Requirements specification
System specification
System integration test plan
Acceptance test plan
Service
System design
Acceptance test
©Ian Sommerville 2004
Detailed design
Sub-system integration test plan
System integration test
Module and unit code and test
Sub-system integration test
Software Engineering, 7th edition.
Slide 33
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.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 34
System evolution
Define system requirements
Assess existing systems
Propose system changes
Existing systems
©Ian Sommerville 2004
Modify systems
New system
Software Engineering, 7th edition.
Slide 35
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 practive perspective that suggests good practice.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 36
RUP phase model
Phase iteration
Inception
Elaboration
©Ian Sommerville 2004
Construction
Software Engineering, 7th edition.
Transition
Slide 37
RUP phases ●
Inception •
●
Elaboration •
●
Develop an understanding of the problem domain and the system architecture.
Construction •
●
Establish the business case for the system.
System design, programming and testing.
Transition •
Deploy the system in its operating environment.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 38
RUP good practice ● ● ● ● ● ●
Develop software iteratively Manage requirements Use component-based architectures Visually model software Verify software quality Control changes to software
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 39
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 are developed to model the system requirements.
Analysis and design
A design model is created and documented using architectural models, component models, object models and sequence models.
Implementation
The components in the system are implemented and structured into implementation sub-systems. Automatic code generation from design models helps accelerate this process.
Test
Testing is an iterative process that is carried out in conjunction with implementation. System testing follows the completion of the implementation.
Deployment
A product release is created, distributed to users and installed in their workplace.
Configuration and change management
This supporting workflow managed changes to the system (see Chapter 29).
Project management
This supporting workflow manages the system development (see Chapter 5).
Environment
This workflow is concerned with making appropriate software tools available to the software development team.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 40
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.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 41
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.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 42
CASE classification ●
●
Classification helps us understand the different types of CASE tools and their support for process activities. Functional perspective •
●
Process perspective •
●
Tools are classified according to their specific function. Tools are classified according to process activities that are supported.
Integration perspective •
Tools are classified according to their organisation into integrated units.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 43
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
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 44
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
©Ian Sommerville 2004
Design
Implementation
Verification and Validation
Software Engineering, 7th edition.
Slide 45
CASE integration ●
Tools •
●
Workbenches •
●
Support individual process tasks such as design consistency checking, text editing, etc. 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.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 46
Tools, workbenches, environments CASE technology
Workbenches
Tools
Editors
Compilers
File comparators
Analysis and design
Multi-method workbenches
©Ian Sommerville 2004
Integrated environments
Programming
Single-method workbenches
Environments
Process-centred environments
Testing
General-purpose workbenches
Software Engineering, 7th edition.
Language-specific workbenches
Slide 47
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 componentbased software engineering. Iterative process models describe the software process as a cycle of activities.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 48
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.
©Ian Sommerville 2004
Software Engineering, 7th edition.
Slide 49
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