Chapter 2 Software Processes Slid
Objectives l l To introduce software process models. To describe a number of generic process models and when they may be used. To outline lower-level process models for (1) requirements engineering, (2) software development, (3) testing, and (4) evolution. To introduce CASE technology to support software process activities Chapter 2 Software Processes Slid
Topics covered l l l l Software process models Process iteration Software specification Software design and implementation Software verification & validation Software evolution Automated process support Chapter 2 Software Processes Slid
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[struhk-cherd] –adjective; having a clearly defined structure or organization. The software process l l A process is a structured set of activities required to develop a software system. Many different software processes, but all involve: • • l l Specification – defining what the system should do; Design & implementation; Validation – checking that it does what the customer wants; Evolution – changing the system in response to changing customer needs. A process model is an abstract representation of a process. It presents a description of a process from some particular perspective Models should be as simple as possible, but no simpler. – A. Einstein Chapter 2 Software Processes Slid
![[struhk-cherd] –adjective; having a clearly defined structure or organization. The software process l l](https://present5.com/presentation/a2e6548fc4a48f519b1f7bdae27589cd/image-5.jpg "[struhk-cherd] –adjective; having a clearly defined structure or organization. The software process l l")
[struhk-cherd] –adjective; having a clearly defined structure or organization. The software process l l A process is a structured set of activities required to develop a software system. Many different software processes, but all involve: • • l l Specification – defining what the system should do; Design & implementation; Validation – checking that it does what the customer wants; Evolution – changing the system in response to changing customer needs. A process model is an abstract representation of a process. It presents a description of a process from some particular perspective Models should be as simple as possible, but no simpler. – A. Einstein Chapter 2 Software Processes Slid
Plan-driven and agile processes l l Plan-driven processes: all of the process activities are planned in advance and progress is measured against this plan. Agile processes: planning is incremental and it is easier to change the process to reflect changing customer requirements. In practice, most practical processes include elements of both plan-driven and agile approaches. There are no right or wrong software processes. Chapter 2 Software Processes Slid
Generic software process models l The Waterfall Model – plan-driven model; separate and distinct phases of specification and development. l Traditionally: not iterative. Incremental Development – specification, development, & validation are interleaved; may be plan-driven or agile. l Reuse-Based Development – e. g. , component-based: the system is assembled from existing components; may be plandriven or agile. l In practice, most large systems are developed using a process that incorporates elements from all of these models. (And, at no additional cost: Boehm’s Spiral Model. ) Chapter 2 Software Processes Slid
Waterfall model (W. Royce) Chapter 2 Software Processes Slid
Waterfall model phases l There are separate phases in the waterfall model: • • • l l Requirements analysis and definition System and software design Implementation and unit testing Integration and system testing Operation and maintenance The waterfall model is mostly used for large systems engineering projects where a system is developed at several sites. In those circumstances, the plan-driven nature of the waterfall model helps coordinate the work. Chapter 2 Software Processes Slid
Waterfall model problems l Inflexible partitioning of the project into distinct stages makes it difficult to respond to changing customer requirements. • • l Thus, this model is only appropriate when the requirements are well-understood (to begin with). Few business systems have stable requirements. ----------------------In general, the drawback of the waterfall model is the difficulty of accommodating change after the process is underway. Chapter 2 Software Processes Slid
Incremental development (cont'd) Chapter 2 Software Processes Slid
Incremental development benefits l The cost of accommodating changing customer requirements is reduced - amount of analysis and documentation that has to be redone is much less than is required with the waterfall model. l It is easier to get customer feedback - customers can comment on demonstrations of the software and see how much has been implemented. l More rapid delivery and deployment of useful software to the customer is possible - customers are able to use and gain value from the software earlier than is possible with a waterfall process. Chapter 2 Software Processes Slid
Incremental development problems l Lack of process visibility - managers need regular deliverables to measure progress. If systems are developed quickly, it is not cost-effective to produce documents that reflect every version of the system. l System structure tends to degrade as new increments are added - unless time and money is spent on refactoring to improve the software, regular change tends to corrupt its structure. Incorporating further software changes becomes increasingly difficult and costly. Chapter 2 Software Processes Slid
Reuse-oriented software engineering l Based on systematic (as opposed to serendipitous) reuse - systems are integrated from existing components or COTS (Commercial-off-the-shelf) systems. l Process stages • • l Component analysis (what’s available? ) Requirements modification (why? ) System design with reuse Development and integration Reuse is now the standard approach for building many types of business systems. (cont'd) Chapter 2 Software Processes Slid
Reuse-oriented software engineering (what’s available? ) (cont'd) Chapter 2 Software Processes Slid
Types of reusable software components l l l Web services that are developed according to service standards and which are available for remote invocation. Collections of objects that are developed as a package to be integrated with a component framework such as. NET or J 2 EE. Stand-alone software systems (COTS) that are configured for use in a particular environment. Chapter 2 Software Processes Slid
Process activities l l Real software processes are interleaved sequences of technical, collaborative and managerial activities with the overall goal of specifying, designing, implementing and testing a software system. The four basic process activities of specification, development, validation and evolution are organized differently in different development processes. In the waterfall model, they are organized in sequence; in incremental development they are interleaved. Chapter 2 Software Processes Slid
Software specification / RE l l The process of establishing what services are required and the constraints on the system’s operation and development. Requirements Engineering (RE) process: • • Feasibility (technical and otherwise) study Requirements elicitation and analysis Requirements specification (documentation) Requirements validation (cont'd) Chapter 2 Software Processes Slid
The requirements engineering process Chapter 2 Software Processes Slid
Software design and implementation l The process of producing an executable system based on the specification • Software design – design a software structure that realizes the specification. • Implementation – translate this structure into an executable program. l The activities of specification, design, and implementation are closely related and may be interleaved. Chapter 2 Software Processes Slid
Design activities l l Architectural design: identify overall structure of system, principal components (sometimes called sub-systems or modules), their relationships, and how they are distributed. Interface design: define the interfaces between system components. Component design: design how each system component will operate. Database design: design the system data structures and how these are to be represented in a database. Chapter 2 Software Processes Slid
Software verification & validation l l l Verification and validation (V&V) determines whether or not a system (1) conforms to its specification and (2) meets the requirements of the customer. Involves checking processes (e. g. , inspections/reviews and program (machine-based) testing. Testing is the most commonly used V&V activity and involves executing program elements with test cases that are derived from specifications and/or program logic. Chapter 2 Software Processes Slid
Testing stages l Development or component testing • • l Individual components are tested independently; Components may be functions or objects or coherent groupings of these entities. System testing • l 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 Chapter 2 Software Processes Slid
Software evolution (maintenance) l l l Software is inherently flexible and subject to change. As requirements change through changing business circumstances, the software that supports the business must also evolve and change. The distinction between development and evolution is increasingly irrelevant as fewer and fewer systems are completely new. (cont'd) Chapter 2 Software Processes Slid
Software evolution (maintenance) e. g. , change requests Chapter 2 Software Processes Slid
Coping with change l Change is inevitable in all large software projects. • • New technologies open up new possibilities for improving implementations. • l Business changes lead to new and changed system requirements. Changing platforms require application changes. Change costs include both rework (e. g. re-analyzing requirements) and the cost of implementing new functionality. Chapter 2 Software Processes Slid
Reducing the costs of rework l Change avoidance: process includes activities that can anticipate possible changes before significant rework is required. • l For example, a prototype system may be developed to stimulate user/stakeholder abticipation. Change tolerance: process is designed so that changes can be accommodated at relatively low cost. • • Proposed changes may be implemented in increments that have not yet been developed. Information hiding techniques may be employed. Chapter 2 Software Processes Slid
Software prototyping Chapter 2 Software Processes Slid
What is prototyping? l An iterative process emphasizing: • Rapid development • Concreteness and Evaluative use (a “real system” is developed and presented to real users for evaluation) • Consideration of alternatives • Feedback • Modification Chapter 2 Software Processes Slid
General Prototyping process What to include & what NOT to include. Chapter 2 Software Processes Slid
Uses of prototypes l Principal use is to help customers and developers better understand system requirements. • • Experimentation stimulates anticipation of how a system could be used. Attempting to use functions together to accomplish some task can easily reveal requirements problems. (Cont’d) Chapter 2 Software Processes Slid
Uses of prototypes (cont’d) l Other potential uses: 1. Evaluating proposed solutions for feasibility (Experimental Prototyping) 2. Develop and evaluate UI designs 3. “Back-to-back” testing 4. Training users before system delivery l Prototyping is most often undertaken as a risk reduction activity. Chapter 2 Software Processes Slid
Classifying prototypes l l By purpose: • Throw-away prototyping – to elicit and validate requirements • Experimental prototyping – to evaluate proposed solutions for feasibility, performance, etc. horizontal vs. vertical (breadth vs. depth) mockups vs. breadboards (form vs. function) “Wizard of Oz” prototyping (Turing test reversed) Chapter 2 Software Processes Slid
Throw-away prototyping Elicit/validate REQMTS Chapter 2 Software Processes Slid
Classifying prototypes l l By purpose: • Throw-away prototyping – to elicit and validate requirements • Experimental prototyping – to evaluate proposed solutions for feasibility, performance, etc. horizontal vs. vertical (breadth vs. depth) mockups vs. breadboards (form vs. function) “Wizard of Oz” prototyping (Turing test reversed) Chapter 2 Software Processes Slid
Classifying prototypes l l By purpose: • Throw-away prototyping – to elicit and validate requirements • Experimental prototyping – to evaluate proposed solutions for feasibility, performance, etc. horizontal vs. vertical (breadth vs. depth) mockups vs. breadboards (form vs. function) “Wizard of Oz” prototyping (Turing test reversed) Chapter 2 Software Processes Slid
Vertical prototype high F I d e l I t y points of comparable effort Horizontal prototype low few Number of features many
Classifying prototypes l l By purpose: • Throw-away prototyping – to elicit and validate requirements • Experimental prototyping – to evaluate proposed solutions for feasibility, performance, etc. horizontal vs. vertical (breadth vs. depth) mockups vs. breadboards (form vs. function) “Wizard of Oz” prototyping (Turing test reversed) Chapter 2 Software Processes Slid
Quin Tech “Self-service check-in and baggage drop-off design” “The design was tested through a full-scale mock-up. ” Chapter 2 Software Processes Slid
Electronic circuit on a breadboard (REUK. co. uk) “There is no need to solder anything, and the components can be moved around and the circuit modified thousands of times without damaging parts. ” Chapter 2 Software Processes Slid
Classifying prototypes l l By purpose: • Throw-away prototyping – to elicit and validate requirements • Experimental prototyping – to evaluate proposed solutions for feasibility, performance, etc. horizontal vs. vertical (breadth vs. depth) mockups vs. breadboards (form vs. function) “Wizard of Oz” prototyping (Turing test reversed) Chapter 2 Software Processes Slid
The Wizard of Oz exposed… “The truth is the Wizard was an illusion created by a man hidden behind a curtain. ” Chapter 2 Software Processes Slid
Prototyping versus simulation l What’s the difference between prototyping and simulation? Chapter 2 Software Processes Slid
Throw-away prototype delivery ? l l Developers may be pressurized to deliver a throwaway prototype as the final system. This is problematic. . . • It may be impossible to meet non-functional requirements. • The prototype is almost certainly undocumented. • The system may be poorly structured and therefore difficult to maintain. • Normal organizational quality standards may not have been applied. Chapter 2 Software Processes Slid
No, no! I won’t deliver the prototype to you! User Mgmt Developer Air Tank Pressurizing the Developer
Implementation techniques l Various techniques may be used for developing prototypes: • • • l l Dynamic high-level languages Database programming (RAD) Component and application assembly These are not mutually exclusive – they are often used together. Visual programming is also an inherent part of most prototype development systems. Chapter 2 Software Processes Slid
Incremental delivery l l l Rather than deliver the system as a single unit, the development and delivery is broken down into increments, each of which incorporates part of the required functionality. User requirements are prioritized and the highest priority requirements are included in early increments. Once the development of an increment is started, its requirements are “frozen” while requirements for later increments can continue to evolve. (Compromise between Waterfall & Evolutionary development) (cont'd) Chapter 2 Software Processes Slid
Incremental delivery (cont'd) Chapter 2 Software Processes Slid
Incremental delivery advantages l l Useful functionality is delivered with each increment, so customers derive value early. 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. (they're subject to more “validation” steps) (cont'd) Chapter 2 Software Processes Slid
Potential problem with incremental delivery l Requirements may NOT be partitionable into standalone increments. (e. g. , a compiler) (A generalization of incremental delivery, known as Incremental Software Development, is discussed in Chap. 17, Rapid Software Development. ) Chapter 2 Software Processes Slid
Extreme programming (Beck ’ 99) l Recent evolution of incremental approach based on • • l l l Development and delivery of very small increments of functionality Significant customer involvement in process Constant code improvement Egoless, pair-wise programming NOT document-oriented Gaining acceptance in some small (and now medium sized) organizations. Representative of the “Agile” development paradigm. www. agilealliance. org Chapter 2 Software Processes Slid
Boehm’s spiral development l l Process is represented as a spiral rather than a sequence of activities. 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. Explicitly incorporates risk assessment and resolution throughout the process. (cont'd) Chapter 2 Software Processes Slid
Spiral model of the software process Chapter 2 Software Processes Slid
Spiral model quadrants l Objective Setting – specific objectives for the phase are identified. l Risk Assessment and Reduction – risks are assessed and activities put in place to reduce the key risks. l Development and Validation – a development model for the system is chosen which can be any of the generic models. l Planning – the project is reviewed and the next phase of the spiral is planned. Chapter 2 Software Processes Slid
The Rational Unified Process l l 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 practice perspective that suggests good practice. A hybrid process model that brings together elements from all of the generic process models…represents a new generation of generic processes (cont'd) Chapter 2 Software Processes Slid
RUP phase model cf Waterfall Model: RUP phases are more closely related to business rather than technical concerns. (cont'd) Chapter 2 Software Processes Slid
RUP phases l Inception • l Elaboration • l Develop an understanding of the problem domain and the system architecture. Construction • l Establish the business case for the system. System design, programming and testing. Transition • Deploy the system in its operating environment. (cont'd) Chapter 2 Software Processes Slid
RUP good practice l l Develop software iteratively Manage requirements Use component-based architectures Visually model software (e. g. , UML packages, sequence models, state machine models) l l Verify software quality Control changes to software (cont'd) Chapter 2 Software Processes Slid
Static workflows (process activities) Chapter 2 Software Processes Slid
Automated process support (CASE) l l Computer-aided software engineering (CASE) is software to support software development and evolution processes. Activity automation (examples): • • • Graphical editors for system model development Data dictionaries for name management GUI builders for user interface construction Debuggers to support program fault finding Automated translators to generate new versions of a program (e. g. , restructuring tools) Chapter 2 Software Processes Slid
CASE technology l CASE technology has led to significant improvements in the software process, but not the order of magnitude improvements that were once predicted. • • Software engineering involves design activity requiring 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 support this well. Chapter 2 Software Processes Slid
CASE classification l l Classification helps us understand the different types of CASE tools / systems 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 – CASE systems are classified according to their breadth of support for the software process. Chapter 2 Software Processes Slid
Functional tool classification TOOL TYPES: Planning tools Editing tools Change mgmt tools Configuration mgmt tools Prototyping tools Method-support tools Language-processing tools Program analysis tools Testing tools Debugging tools Documentation tools Reengineering tools EXAMPLES: PERT tools, estimation tools, spreadsheets Text editors, diagram editors, word processors Rqmts traceability tools, change control sys Version mgmt systems, system building tools V. high-level langs, user interface generators Design editors, data dicts, code generators Compilers, interpreters Cross ref generators, static/dynamic analyzers Test data generators, file comparators Interactive debugging systems Page layout programs, image editors Cross-ref systems, program restructuring systems Chapter 2 Software Processes Slid
Activity-based classification Actually far more lower CASE tools than upper CASE
CASE integration l l l 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. Chapter 2 Software Processes Slid
Tools, workbenches, environments Chapter 2 Software Processes Slid
Key points l l Software processes are the activities involved in producing and evolving a software system. They are represented in a software process model. Fundamental (lower level) activities are specification, design and implementation, validation & verification, and evolution. Generic models are very general process models representing different approaches to development. Iterative process models describe the software process as a cycle of activities. Chapter 2 Software Processes Slid
Key points (cont’d) l l l Requirements engineering is the process of establishing what services are required and the constraints on the system’s operation and development. Design and implementation processes produce an executable system based on the specification. V&V involves checking that the system meets its specification and satisfies user needs. Evolution is concerned with modifying the system after it is placed in use. CASE technology supports software process activities. Chapter 2 Software Processes Slid
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