Software Processes PDF

10/18/2021 The software process  Software processes are a set of related activities involved in...

10/18/2021 The software process  Software processes are a set of related activities involved in producing a software system. Software Processes  There is no universal software engineering method for different software systems type, but  Fundamental software engineering activities are: Software process models  Specification – defining what the system should do;  Design and implementation – defining the organization of the Process activities system and implementing the system; Coping with change  Validation – checking that it does what the customer wants;  Evolution – changing the system in response to changing Process improvement customer needs.  A software process model is an abstract representation of a process. It presents a description of a process from some particular perspective. Dr. Noha Adly CSE 322 - Software Processes 1 Dr. Noha Adly CSE 322 - Software Processes 2 1 2 Software process descriptions Plan-driven and agile processes  When we describe and discuss processes, we usually talk  Plan-driven processes are processes where all of the about the activities in these processes such as specifying a process activities are planned in advance and progress is data model, designing a user interface, etc. and the ordering measured against this plan. of these activities.  In agile processes, planning is incremental and continual  Activities are complex and include sub-activities such as as the software develops and it is easier to change the requirements validation, architectural design, unit testing, etc. process to reflect changing customer requirements.  Process descriptions may also include:  For safety-critical systems, a very structured development  Products or deliverables, which are the outcomes of a process process is required. For business systems, with rapidly activity; e.g a model of the software architecture changing requirements, a more flexible, agile process is  Roles, which reflect the responsibilities of the people involved in likely to be better the process; e.g project manager, configuration manager, programmer  Pre- and post-conditions, which are statements that are true  There are no right or wrong software processes. before and after a process activity has been enacted or a  In practice, most practical processes include elements of product produced. Dr. Noha Adly CSE 322 - Software Processes 3 both plan-driven andCSEagile Dr. Noha Adly approaches. 322 - Software Processes 4 3 4 1  10/18/2021 Software process models The waterfall model  The waterfall model  Plan-driven model. Separate and distinct phases of specification and development.  Incremental development  Specification, development and validation are interleaved. May be plan-driven or agile.  Integration and configuration  The system is assembled from existing configurable components. May be plan-driven or agile.  In practice, most large systems are developed using a process that incorporates elements from all of these models. Dr. Noha Adly CSE 322 - Software Processes 5 Dr. Noha Adly CSE 322 - Software Processes 6 5 6 Waterfall model phases The Waterfall Model  There are separate identified phases in the waterfall model:  The main drawback of the waterfall model is the difficulty  Requirements analysis and definition of accommodating change after the process is underway.  System and software design  Inflexible partitioning of the project into distinct stages makes it  Implementation and unit testing difficult to respond to changing customer requirements.  Integration and system testing  Therefore, this model is only appropriate when the requirements  Operation and maintenance are well-understood and changes will be fairly limited during the All Process activities must be planned and scheduled before design process. E.g. Embedded systems and Critical safety starting development systems  Few business systems have stable requirements. Result of each phase is one or more documents that are approved (‘signed off’).  The waterfall model is mostly used for large systems The following phase should not start until the previous phase has engineering projects where a system is developed at finished. several sites.  In those circumstances, the plan-driven nature of the waterfall model helps coordinate the work. Dr. Noha Adly CSE 322 - Software Processes 7 Dr. Noha Adly CSE 322 - Software Processes 8 7 8 2  10/18/2021 Incremental development Incremental development benefits Based on the idea of developing an initial implementation, exposing this to user comment and evolving it through several versions until an adequate system has been developed  The cost of accommodating changing customer Specification, development, and validation activities are interleaved rather than separate, requirements is reduced. with rapid feedback across activities.  The amount of analysis and documentation that has to be redone is much less than is required with the waterfall model.  It is easier to get customer feedback on the development work that has been done.  Customers can comment on demonstrations of the software and see how much has been implemented.  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. Dr. Noha Adly CSE 322 - Software Processes 9 Dr. Noha Adly CSE 322 - Software Processes 10 9 10 Incremental development problems Integration and configuration  The process is not visible. Based on software reuse where systems are  Managers need regular deliverables to measure progress. If integrated from existing components or systems are developed quickly, it is not cost-effective to produce documents that reflect every version of the system. application systems (sometimes called COTS – (Commercial-Off-The-Shelf) systems).  System structure tends to degrade as new increments are added. Reused elements may be configured to adapt  Regular change leads to messy code their behaviour and functionality to a user’s  Increasingly costly to add new features requirements  Unless time and money is spent on refactoring to improve the software, regular change tends to corrupt its structure. Reuse is now the standard approach for building  Acute for large complex systems many types of business system Dr. Noha Adly CSE 322 - Software Processes 11 Dr. Noha Adly CSE 322 - Software Processes 12 11 12 3  10/18/2021 Types of reusable software Advantages and disadvantages Stand-alone application systems (COTS) that Advantages are configured for use in a particular  Reduced costs and risks as less software is environment. developed from scratch Collections of objects that are developed as a  Faster delivery and deployment of system package to be integrated with a component Disadvantages framework such as.NET or J2EE.  requirements compromises are inevitable so system may not meet real needs of users Web services that are developed according to  Loss of control over evolution of reused system service standards and which are available for elements remote invocation. Dr. Noha Adly CSE 322 - Software Processes 13 Dr. Noha Adly CSE 322 - Software Processes 15 13 15 Process activities  Real software processes are inter-leaved sequences of technical, collaborative and managerial activities with the overall goal of specifying, designing, implementing and testing a software system. Process activities  The four basic process activities of  Specification  Development  Validation  Evolution are organized differently in different development processes.  In the waterfall model, they are organized in sequence, whereas in incremental development they are interleaved Dr. Noha Adly CSE 322 - Software Processes 16 Dr. Noha Adly CSE 322 - Software Processes 17 16 17 4  10/18/2021 Software specification Requirement Engineering Activities  The process of establishing what services are required and identifying  Requirements elicitation and analysis the constraints on the system’s operation and development.  What do the system stakeholders require or expect from the system?  Requirements engineering is the process of developing a software  Done through observation of existing systems, discussions with potential specification. users and procurers, task analysis, and so on.  may involve the development of system models and prototypes.  Critical stage as a mistake leads to later problem in design and implementation  Requirements specification  A feasibility study is carried out before the requirement engineering to  Defining the requirements in detail trough translation of information gathered during the analysis activity assess whether there is a market need and whether it is realistic technically and financially  Two types of requirements may be included User requirements: abstract statements of the system  Requirements are usually presented at two levels of detail. system requirements: more detailed description of the functionality  End-users and customers with a high-level statement of the requirements  Requirements validation  System developers with a more detailed system specification.  Checking the validity of the requirements for realism, consistency, and completeness. Dr. Noha Adly CSE 322 - Software Processes 18 Dr. Noha Adly CSE 322 - Software Processes 19 18 19 The requirements engineering process 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;  Describe data models and structures  Define interfaces between components  Design is developed in stages with constant backtracking  Implementation  Translate this structure into an executable program;  The activities of design and implementation are closely related and may be inter-leaved. Dr. Noha Adly CSE 322 - Software Processes 20 Dr. Noha Adly CSE 322 - Software Processes 21 20 21 5  10/18/2021 A general model of the design process Design Inputs  Most software interfaces with other software systems. These include the operating system, database, middleware, and other application systems. These make up the ‘software platform’, the environment in which the software will execute.  Information about this platform is an essential input to the design process, as designers must decide how best to integrate it with the software’s environment.  The requirements specification is a description of the functionality the software must provide and its performance and dependability requirements.  If the system is to process existing data, then the description of that data may be included in the platform specification; otherwise, the data description must be an input to the design process so that the system data organization to be defined. Dr. Noha Adly CSE 322 - Software Processes 22 Dr. Noha Adly CSE 322 - Software Processes 23 22 23 Design activities A general model of the design process  Architectural design, where you identify the overall structure of the system, the principal components (subsystems or modules), their relationships and how they are distributed.  Database design, where you design the system data structures and how these are to be represented in a database.  Interface design, where you define the interfaces between system components.  Component selection and design, where you search for reusable components. If unavailable, you design how it will operate.  The design process activities are both interleaved and interdependent. Dr. Noha Adly CSE 322 - Software Processes 24 Dr. Noha Adly CSE 322 - Software Processes 25 24 25 6  10/18/2021 System implementation Software validation  The software is implemented either by developing a  Verification and validation (V & V) is intended to show program or programs or by configuring an application that a system conforms to its specification and meets the system. requirements of the system customer.  Design and implementation are interleaved activities for  Involves checking and review processes and system most types of software system. testing.  Programming is an individual activity with no standard  System testing involves executing the system with test process. cases that are derived from the specification of the real  Debugging is the activity of finding program faults and data to be processed by the system. correcting these faults.  Testing is the most commonly used Validation technique. Dr. Noha Adly CSE 322 - Software Processes 26 Dr. Noha Adly CSE 322 - Software Processes 27 26 27 Testing phases in a plan-driven software Testing stages process (V-model)  Component testing Testing is driven by a set of plans  Individual components are tested independently; Independent team of testers work from these pre-formulated test plans  Components may be functions or objects or coherent groupings of these entities.  System testing: Testing of the system as a whole.  Testing interactions between components  Showing that the system meets its functional and non functional requirements  Testing of emergent properties.  Customer testing: Testing with real data to check that the system meets the customer’s needs. (Alpha and Beta testing) Dr. Noha Adly CSE 322 - Software Processes 28 Dr. Noha Adly CSE 322 - Software Processes 29 28 29 7  10/18/2021 Software evolution System evolution  Software is inherently flexible and can change – Rather than two separate processes, it is more realistic to think of compared to hardware system software engineering as an evolutionary process where software is continually changed over its lifetime in response to changing  As requirements change through changing business requirements and customer needs. circumstances, the software that supports the business must also evolve and change.  Although there has been a split between development and evolution (maintenance) - this is increasingly irrelevant as very few systems are completely new.  it makes much more sense to see development and maintenance as a continuum Dr. Noha Adly CSE 322 - Software Processes 30 Dr. Noha Adly CSE 322 - Software Processes 31 30 31 Coping with change  Change is inevitable in all large software projects.  Business changes lead to new and changed system requirements  New technologies open up new possibilities for improving Coping with change implementations  Changing platforms require application changes  Whatever software process model is used, it is essential that it can accommodate changes to the software  Change leads to rework so the costs of change include both rework (e.g. re-analysing requirements) as well as the costs of implementing new functionality Dr. Noha Adly CSE 322 - Software Processes 32 Dr. Noha Adly CSE 322 - Software Processes 33 32 33 8  10/18/2021 Reducing the costs of rework Software prototyping  Change anticipation, where the software process  A prototype is an initial version of a system used to includes activities that can anticipate possible changes demonstrate concepts and try out design options. before significant rework is required.  A prototype can be used to anticipate changes in:  For example, a prototype system may be developed to show some key features of the system to customers. They can  The requirements engineering process to help with experiment with the prototype and refine their requirements requirements elicitation and validation; before committing to high software production costs.  In design processes to  Change tolerance, where the process is designed so that explore software solutions changes can be accommodated at relatively low cost. development of a UI design for the system  This normally involves some form of incremental development.  In the testing process to run back-to-back tests. Proposed changes may be implemented in increments that have not yet been developed. If this is impossible, then only a single increment (a small part of the system) may have to be altered to incorporate the change. Dr. Noha Adly CSE 322 - Software Processes 34 Dr. Noha Adly CSE 322 - Software Processes 36 34 36 Software prototyping The process model of prototype development Qu Quick i ck p l an Com m u n icat io n plan communication Modeling Mo d e li n g Q u ic k d e si g n Quick design Deployment Deployment D e live r y delivery & Co n st r uct io n & Fe e db ack Construction feedback of of p r oprototype t o t yp e  May be based on rapid prototyping languages or tools Dr. Noha Adly CSE 322 - Software Processes 37 Dr. Noha Adly CSE 322 - Software Processes 38 37 38 9  10/18/2021 Prototype development Throw-away prototypes  Decide objective of prototype before start Prototypes should be discarded after  E.g. To develop user interface, Validate some functional system development as they are not a good basis for a requirements, demonstrate applications to managers, etc production system:  The same prototype cannot meet all objectives.  If the objectives are left unstated, management or end-users may  It may be impossible to tune the system to meet non- misunderstand the function of the prototype. Consequently, they functional requirements; may not get the benefits that they expected from the prototype  Prototypes are normally undocumented; development.  The prototype structure is usually degraded through  Decide on functionality to include and what to leave out rapid change;  should focus on areas of the product that are not well-understood  The prototype probably will not meet normal  Error checking and recovery may not be included in the prototype; organizational quality standards.  Focus on functional rather than non-functional requirements such as reliability and security Dr. Noha Adly CSE 322 - Software Processes 39 Dr. Noha Adly CSE 322 - Software Processes 41 39 41 Incremental delivery 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.  increments are delivered and deployed for use in a real operational environment  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.  Experimenting with the system helps them clarify their requirements for later system increments  Architectural design must be open and completed before the implementation for the various increments commences. Dr. Noha Adly CSE 322 - Software Processes 42 Dr. Noha Adly CSE 322 - Software Processes 43 42 43 10  10/18/2021 Incremental delivery Incremental delivery advantages  One of the main advantages of the incremental models  Customer value can be delivered with each increment so is their ability to cope with change during the system functionality is available earlier. development of the system.  Early increments act as a prototype to help elicit  As an example, consider an error in the requirements. requirements for later increments.  With the waterfall model, the error may not be noticed until  Lower risk of overall project failure. acceptance testing, when it is probably too late to correct it. (Note that the client probably does not see the software running  The highest priority system services tend to receive the until the acceptance tests.) most testing.  In the incremental model, there is a good chance that a requirements error will be recognized as soon as the corresponding software is incorporated into the system. Dr. Noha Adly CSE 322 - Software Processes 44 Dr. Noha Adly CSE 322 - Software Processes 45 44 45 Incremental delivery disadvantages  Difficult to implement for existing systems as increments have less functionality than the system being replaced.  Most systems require a set of basic facilities that are used by different parts of the system. Process improvement  As requirements are not defined in detail until an increment is to be implemented, it can be hard to identify common facilities that are needed by all increments.  The essence of iterative processes is that the specification is developed in conjunction with the software.  However, this conflicts with the procurement model of many organizations, where the complete system specification is part of the system development contract. Dr. Noha Adly CSE 322 - Software Processes 46 Dr. Noha Adly CSE 322 - Software Processes 47 46 47 11  10/18/2021 Process improvement Approaches to improvement  Process improvement means understanding existing  The process maturity approach, which focuses on processes and changing these processes to increase improving process and project management and product quality and/or reduce costs and development introducing good software engineering practice time.  The level of process maturity reflects the extent to which good technical and management practice has been adopted in  Many software companies have turned to software organizational software development processes. process improvement as a way of enhancing the quality of their software, reducing costs or accelerating their  The agile approach, which focuses on iterative development processes. development and the reduction of overheads in the software process.  The principal approaches to process improvement are  The primary characteristics of agile methods are rapid delivery of agile approaches, geared to reducing process functionality and responsiveness to changing customer overheads, and maturity-based approaches based on requirements. better process management and the use of good software engineering practice. Dr. Noha Adly CSE 322 - Software Processes 48 Dr. Noha Adly CSE 322 - Software Processes 49 48 49 The process improvement cycle Process improvement activities  Process measurement  You measure one or more attributes of the software process or product. These measurements forms a baseline that helps you decide if process improvements have been effective.  Process analysis  The current process is assessed, and process weaknesses and bottlenecks are identified. Process models (sometimes called process maps) that describe the process may be developed.  Process change  Process changes are proposed to address some of the identified process weaknesses. These are introduced and the cycle resumes to collect data about the effectiveness of the changes. Dr. Noha Adly CSE 322 - Software Processes 50 Dr. Noha Adly CSE 322 - Software Processes 51 50 51 12  10/18/2021 Software Engineering Institute (SEI) Process measurement Capability maturity levels  Wherever possible, quantitative process data should be collected  The SEI process maturity framework identifies maturity  However, where organisations do not have clearly defined process levels that essentially correspond standards this is very difficult as you don’t know what to measure. A to the use of good software process may have to be defined before any measurement is possible. engineering practice.  Process measurements should be used to assess process  The maturity of a software improvements company processes reflects the  But this does not mean that measurements should drive the process management, improvements. The improvement driver should be the organizational measurement and use of good objectives. software engineering practice in the company  Process metrics  Time taken for process activities to be completed e.g Calendar time or effort to complete an activity or process  Resources required for processes or activities e.g. Total effort in person- days  Number of occurrences of a particular event e.g. Number of defects discovered Dr. Noha Adly CSE 322 - Software Processes 52 Dr. Noha Adly CSE 322 - Software Processes 53 52 53 The SEI capability maturity model Process Assessment and Improvement  Initial - Essentially uncontrolled: goals associated with the process are satisfied,  CMM-Based Appraisal for Internal Process Improvement (CBA IPI)— the scope of work to is explicitly set out and communicated to the team members provides a diagnostic technique for assessing the relative maturity of a software organization; uses the SEI CMM as the basis for the  Managed - Product management procedures defined and used: goals assessment associated with the process are met and organizational policies are in place that define when each process should be used. There must be documented project plans that define  Standard CMMI Assessment Method for Process Improvement (SCAMPI) the project goals. Resource management and process monitoring procedures must be in place across the institution. — provides a five step process assessment model that incorporates five phases: initiating, diagnosing, establishing, acting and learning.  Defined - Process management procedures and strategies defined and  SPICE—The SPICE (ISO/IEC15504) standard defines a set of used: Each project has a managed process, adapted to the requirements from a defined set of organizational processes. Process assets and measurements must be collected and requirements for software process assessment. The intent of the used for future process improvements. standard is to assist organizations in developing an objective evaluation of the efficacy of any defined software process.  Quantitatively Managed - Quantitative management strategies defined and used: there is an organizational responsibility to use statistical and other  ISO 9001:2000 for Software—a generic standard that applies to any quantitative methods to control sub-processes organization that wants to improve the overall quality of the products, systems, or services that it provides. Therefore, the standard is directly  Optimising - Process improvement strategies defined and used: Trends applicable to software organizations and companies. must be analyzed and the processes adapted to changing business needs. Dr. Noha Adly CSE 322 - Software Processes 54 Dr. Noha Adly CSE 322 - Software Processes 55 54 55 13  10/18/2021 The Rational Unified Process RUP Phases  RUP is a very general iterative software development process framework based on UML.  A development cycle in RUP has four phases. Each phase usually done in one or more iteration. The end of each phase  It is a hybrid process model that brings together elements from is marked by a milestone.  All of the generic process models (Waterfall and Incremental)  Inception: Create a business case for the project; may involve  illustrates good practice in specification and design requirements analysis, risk analysis, prototyping. Milestone:  Supports prototyping and incremental delivery. (Objectives)  The activities of (requirements, design, implementation, test, etc.)  Elaboration. Develop and analyze models for the S/W; project exist in RUP, but they may occur many times during development. development plans, identify risks, user documentation, release  For example, requirements may be derived for each component many description. Milestone: (requirement model, Architecture, times instead of once only for the entire product. development plan)  Normally described from 3 perspectives  Construction. System design, Coding and quality assurance.  A dynamic perspective that shows phases over time; Milestone: (Operational Capability)  A static perspective that shows process activities;  Transition. Transfer the program or component to the user;  A practice perspective that suggests good practice. ensure that the user has adequate documentation and other resources to make use of it. Milestone: (Release) Dr. Noha Adly CSE 322 - Software Processes 56 Dr. Noha Adly CSE 322 - Software Processes 57 56 57 RUP iteration Static workflows in the RUP  Iteration within the RUP is supported in two ways  The static view of the RUP focuses on the activities that  In-phase iteration: Each phase is iterative with results developed take place during the development process incrementally.  These are called workflows  Cross-phase iteration As shown by the loop in the RUP model, the whole set of phases may be enacted incrementally.  There are six core process workflows identified in the process and three core supporting workflows.  There are two main families of RUP workflows  Engineering  Management  The RUP has been designed in conjunction with the UML, so the workflow description is oriented around associated UML models such as sequence models, object models, etc. Dr. Noha Adly CSE 322 - Software Processes 58 Dr. Noha Adly CSE 322 - Software Processes 59 58 59 14  10/18/2021 Static workflows in the RUP – (Supporting Static workflows in the RUP - Core Management) Workflow Description Workflow Description Business The business processes are modelled using business use cases. Configuration and This supporting workflow managed changes to the modelling change system Requirements Actors who interact with the system are identified and use cases management are developed to model the system requirements. Project This supporting workflow manages the system Analysis and A design model is created and documented using architectural management development design models, component models, object models and sequence models. Environment This workflow is concerned with making appropriate software tools available to the software development Implementation The components in the system are implemented and structured into team. implementation sub-systems. Automatic code generation from design models helps accelerate this process. The advantage in presenting dynamic and static views is that phases of Testing Testing is an iterative process that is carried out in conjunction with the development process are not associated with specific workflows. So, implementation. System testing follows the completion of the implementation. all of the RUP workflows may be active at all stages of the process. In the early phases of the process, most effort will probably be Deployment A product release is created, distributed to users and installed in spent on workflows such as business modelling and requirements their workplace. in the later phases, in testing and deployment. Dr. Noha Adly CSE 322 - Software Processes 60 Dr. Noha Adly CSE 322 - Software Processes 61 60 61 RUP good software engineering practice RUP – Phases versus Workflows – six practices recommended  Develop software iteratively Plan increments based on customer priorities and deliver highest priority increments first.  Manage requirements Explicitly document customer requirements and keep track of changes to these requirements. Analyze the impact of changes on the system before accepting them.  Use component-based architectures Organize the system architecture as a set of reusable components.  Visually model software Use graphical UML models to present static and dynamic views of the software  Verify software quality Ensure that the software meet’s organizational quality standards.  Control changes to software Manage software changes using a change management system and configuration management tools. Dr. Noha Adly CSE 322 - Software Processes 62 Dr. Noha Adly CSE 322 - Software Processes 63 62 63 15