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Software Process Models in Software Engineering
The document introduces software processes, outlining various process models such as waterfall, evolutionary, formal systems, and reuse-oriented development. It highlights the key steps involved in software specification, design, implementation, validation, and the importance of process iteration to adapt to evolving requirements. The content also discusses the testing phases and methods used to ensure software quality and conformity to specifications.
Software Process Models in Software Engineering
- 1. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 1 Software Processes Coherent sets of activities for specifying, designing, implementing and testing software systems
- 2. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 2 Objectives To introduce software process models To describe a number of different process models and when they may be used To describe outline process models for requirements engineering, software development, testing and evolution To introduce CASE technology to support software process activities
- 3. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 3 Topics covered Software process models Process iteration Software specification Software design and implementation Software validation Software evolution Automated process support
- 4. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 4 The software process A structured set of activities required to develop a software system • 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
- 5. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 5 Generic software process models The waterfall model • Separate and distinct phases of specification and development Evolutionary development • Specification and development are interleaved Formal systems development • A mathematical system model is formally transformed to an implementation Reuse-based development • The system is assembled from existing components
- 6. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 6 Waterfall model R e q u i r e m e n t s d e f i n i t i o n S y s t e m a n d s o f t w a r e d e s i g n I m p l e m e n t a t i o n a n d u n i t t e s t i n g I n t e g r a t i o n a n d s y s t e m t e s t i n g O p e r a t i o n a n d m a i n t e n a n c e
- 7. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 7 Waterfall model phases Requirements analysis and definition System and software design Implementation and unit testing Integration and system testing Operation and maintenance The drawback of the waterfall model is the difficulty of accommodating change after the process is underway
- 8. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 8 Waterfall model problems Inflexible partitioning of the project into distinct stages This makes it difficult to respond to changing customer requirements Therefore, this model is only appropriate when the requirements are well-understood
- 9. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 9 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 Throw-away prototyping • Objective is to understand the system requirements. Should start with poorly understood requirements
- 10. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 10 Evolutionary development V a l i d a t i o n F i n a l v e r s i o n D e v e l o p m e n t I n t e r m e d i a t e v e r s i o n s S p e c i f i c a t i o nI n i t i a l v e r s i o n O u t l i n e d e s c r i p t i o n C o n c u r r e n t a c t i v i t i e s
- 11. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 11 Evolutionary development 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
- 12. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 12 Formal systems development Based on the transformation of a mathematical specification through different representations to an executable program Transformations are ‘correctness-preserving’ so it is straightforward to show that the program conforms to its specification Embodied in the ‘Cleanroom’ approach to software development
- 13. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 13 Formal systems development R e q u i r e m e n t s d e f i n i t i o nF o r m a l s p e c i f i c a t i o nF o r m a l t r a n s f o r m a t i o nI n t e g r a t i o n a n d s y s t e m t e s t i n g
- 14. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 14 Formal transformations R 2 F o r m a l s p e c i f i c a t i o n R 3E x e c u t a b l e p r o g r a m P 2P 3P 4 T 1T 2T 3T 4 P r o o f s o f t r a n s f o r m a t i o n c o r r e c t n e s s F o r m a l t r a n s f o r m a t i o n s R 1 P 1
- 15. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 15 Formal systems development Problems • Need for specialised skills and training to apply the technique • Difficult to formally specify some aspects of the system such as the user interface Applicability • Critical systems especially those where a safety or security case must be made before the system is put into operation
- 16. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 16 Reuse-oriented development Based on systematic reuse where systems are integrated from existing components or COTS (Commercial-off-the-shelf) systems Process stages • Component analysis • Requirements modification • System design with reuse • Development and integration This approach is becoming more important but still limited experience with it
- 17. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 17 Reuse-oriented development R e q u i r e m e n t s s p e c i f i c a t i o nC o m p o n e n t a n a l y s i s D e v e l o p m e n t a n d i n t e g r a t i o n S y s t e m d e s i g n w i t h r e u s e R e q u i r e m e n t s m o d i f i c a t i o n S y s t e m v a l i d a t i o n
- 18. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 18 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 development • Spiral development
- 19. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 19 Incremental development 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
- 20. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 20 Incremental development V a l i d a t e i n c r e m e n t D e v e l o p s y s t e m i n c r e m e n t D e s i g n s y s t e m a r c h i t e c t u r e I n t e g r a t e i n c r e m e n t V a l i d a t e s y s t e m D e f i n e o u t l i n e r e q u i r e m e n t sA s s i g n r e q u i r e m e n t s t o i n c r e m e n t s S y s t e m i n c o m p l e t e F i n a l s y s t e m
- 21. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 21 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
- 22. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 22 Extreme programming New approach to 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 pairwise programming
- 23. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 23 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
- 24. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 24 Spiral model of the software process R i s k a n a l y s i s R i s k a n a l y s i s R i s k a n a l y s i s Risk anal ysis P r o t o - t y p e 1 P r o t o t y p e 2 P r o t o t y p e 3 O p e r a - t i o n a l p r o t o y p e C o n c e p t o f O p e r a t i o n S i m u l a t i o n s , m o d e l s , b e n c h m a r k s S / W r e q u i r e m e n t s R e q u i r e m e n t v a l i d a t i o n D e s i g n V & V P r o d u c t d e s i g n D e t a i l e d d e s i g n C o d e U n i t t e s t I n t e g r a t i o n t e s t A c c e p t a n c e t e s t S e r v i c e D e v e l o p , v e r i f y n e x t - l e v e l p r o d u c t E v a l u a t e a l t e r n a t i v e s i d e n t i f y , r e s o l v e r i s k s D e t e r m i n e o b j e c t i v e s a l t e r n a t i v e s a n d c o n s t r a i n t s P l a n n e x t p h a s eI n t e g r a t i o n a n d t e s t p l a n D e v e l o p m e n t p l a n R e q u i r e m e n t s p l a n L i f e - c y c l e p l a n R E V I E W
- 25. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 25 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
- 26. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 26 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
- 27. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 27 The requirements engineering process F e a s i b i l i t y s t u d yR e q u i r e m e n t s e l i c i t a t i o n a n d a n a l y s i sR e q u i r e m e n t s s p e c i f i c a t i o n R e q u i r e m e n t s v a l i d a t i o n F e a s i b i l i t y r e p o r t S y s t e m m o d e l sU s e r a n d s y s t e m r e q u i r e m e n t sR e q u i r e m e n t s d o c u m e n t
- 28. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 28 Software design and implementation The process of converting the system specification into an executable system Software design • Design a software structure that realises the specification Implementation • Translate this structure into an executable program The activities of design and implementation are closely related and may be inter-leaved
- 29. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 29 Design process activities Architectural design Abstract specification Interface design Component design Data structure design Algorithm design
- 30. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 30 The software design process Ar chitectur al design Abstr act specific tion Interfa design Com desig Da ta stru e des A d System ar chitectur eSoftw ar e specific tion Interfa specifi tion Com spec tion Da ta stru e spe tio A sp ti R equir ements specifica tion Desig vitie Desig oduc
- 31. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 31 Design methods Systematic approaches to developing a software design The design is usually documented as a set of graphical models Possible models • Data-flow model • Entity-relation-attribute model • Structural model • Object models
- 32. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 32 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
- 33. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 33 The debugging process L o c a t e e r r o r D e s i g n e r r o r r e p a i rR e p a i r e r r o r R e - t e s t p r o g r a m
- 34. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 34 Software validation Verification and validation 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
- 35. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 35 The testing process S u b - s y s t e m t e s t i n g M o d u l e t e s t i n g U n i t t e s t i n g S y s t e m t e s t i n gA c c e p t a n c e t e s t i n g C o m p o n e n t t e s t i n gI n t e g r a t i o n t e s t i n gU s e r t e s t i n g
- 36. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 36 Testing stages Unit testing • Individual components are tested Module testing • Related collections of dependent components are tested Sub-system testing • Modules are integrated into sub-systems and tested. The focus here should be on interface testing System testing • Testing of the system as a whole. Testing of emergent properties Acceptance testing • Testing with customer data to check that it is acceptable
- 37. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 37 Testing phases R e q u i r e m e n t s s p e c i f i c a t i o nS y s t e m s p e c i f i c a t i o nS y s t e m d e s i g nD e t a i l e d d e s i g nM o d u l e a n d u n i t c o d e a n d t e s s S u b - s y s t e m i n t e g r a t i o n t e s t p l a n S y s t e m i n t e g r a t i o n t e s t p l a n A c c e p t a n c e t e s t p l a n S e r v i c eA c c e p t a n c e t e s t S y s t e m i n t e g r a t i o n t e s tS u b - s y s t e m i n t e g r a t i o n t e s t
- 38. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 38 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
- 39. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 39 System evolution A s s e s s e x i s t i n g s y s t e m s D e f i n e s y s t e m r e q u i r e m e n t s P r o p o s e s y s t e m c h a n g e sM o d i f y s y s t e m s N e w s y s t e m E x i s t i n g s y s t e m s
- 40. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 40 Automated process support (CASE) 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
- 41. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 41 Case technology Case technology has led to significant improvements in the software process though not the order of magnitude improvements that were once predicted • Software engineering requires creative thought - this is not readily automatable • Software engineering is a team activity and, for large projects, much time is spent in team interactions. CASE technology does not really support these
- 42. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 42 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
- 43. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 43 Functional tool classification
- 44. Activity-based classification R e e n g i n e e r i n g t o o ls T e s ti n g t o o ls D e b u g g in g to o l s P r o g r a m a n a l y s is to o l s L a n g u a g e - p r o c e s s in g to o l s M e t h o d s u p p o r tto o l s P r o t o t y p in g t o o ls C o n f ig u r a ti o n m a n a g e m e n tto o l s C h a n g e m a n a g e m e n tt o o ls D o c u m e n t a ti o n t o o ls E d i ti n g t o o ls P la n n i n g t o o ls S p e c if i c a ti o n D e s i g nI m p le m e n ta ti o nV e r i f ic a ti o n a n d V a li d a t io n
- 45. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 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
- 46. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 46 Tools, workbenches, environments S i n g l e - m e t h o d w o r k b e n c h e sG e n e r a l - p u r p o s e w o r k b e n c h e s M u l t i - m e t h o d w o r k b e n c h e s L a n g u a g e - s p e c i f i c w o r k b e n c h e s P r o g r a m m i n gT e s t i n g A n a l y s i s a n d d e s i g n I n t e g r a t e d e n v i r o n m e n t sP r o c e s s - c e n t r e d e n v i r o n m e n t s F i l e c o m p a r a t o r s C o m p i l e r s E d i t o r s E n v i r o n m e n t s W o r k b e n c h e s T o o l s C A S E t e c h n o l o g y
- 47. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 Slide 47 Key points Software processes are the activities involved in producing and evolving a software system. They are represented in a software process model General activities are specification, design and implementation, validation and evolution Generic process models describe the organisation of software processes Iterative process models describe the software process as a cycle of activities
- 48. ©Ian Sommerville 2000Software Engineering, 6th edition. Chapter 1 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 CASE technology supports software process activities