Chapter 2 Software Processes PDF

Chapter 2 Software Processes Chapter 2 Software 11/24/2024 1 Process_Dr.asmaa Topics covered  Software process models  Process activities  Coping with change  Process improvement Chapter...

Chapter 2 Software Processes Chapter 2 Software 11/24/2024 1 Process_Dr.asmaa Topics covered  Software process models  Process activities  Coping with change  Process improvement Chapter 2 Software 11/24/2024 2 Process_Dr.asmaa  The software process  A structured set of activities is required to develop a software system.  Many different software processes but all involve: 1. Specification – defining what the system should do; 2. Design and implementation(Software development) – The software to meet the specification must be produced and implemented the system; 3. Validation – The software must be validated to ensure that it does what the customer wants 4. Evolution – The software must evolve to meet changing customer needs.  A software process model is an abstract representation of a process. It presents a description of a process from some particular perspective. Chapter 2 Software 11/24/2024 3 Process_Dr.asmaa  Software process descriptions  When we describe and discuss processes, we usually talk about the activities in these processes such as specifying a data model, designing a user interface, etc., and the ordering of these activities.  Process descriptions may also include: 1. Products are the outcomes of a process activity; For example, the outcome of the activity of architectural design may be a model of the software architecture. 2. Roles, that reflect the responsibilities of the people involved in the process; Examples of roles are project manager, configuration manager, and programmer. 3. Pre- and post-conditions are conditions that must be held before and after a process activity has been enacted or a product produced. For example, before architectural design begins, a precondition may be that the consumer has approved all requirements; after this activity is finished, a post- condition might be that the UML Chapter models2 Software describing the architecture have been reviewed. 11/24/2024 Process_Dr.asmaa 4 Plan-driven and agile processes  Plan-driven processes are processes where all of the process activities are planned in advance and progress is measured against this plan. ‫خطوة خطوة مع الخطة‬  In agile processes, planning is incremental and it is easier to change the process to reflect changing customer requirements. ‫التخطيط تدريجي لتعكس متطلبات‬ ‫العمالء المتغيرة‬.  There are no right or wrong software processes. Chapter 2 Software 11/24/2024 5 Process_Dr.asmaa  Software process models Chapter 2 Software 11/24/2024 6 Process_Dr.asmaa  Software process models 1- The waterfall model  Plan-driven model. Separate and distinct phases of specification and development. 2- Incremental development  Specification, development and validation are interleaved. May be plan- driven or agile. 3- 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. Chapter 2 Software 11/24/2024 7 Process_Dr.asmaa 1- The waterfall model Chapter 2 Software 11/24/2024 8 Process_Dr.asmaa  Waterfall model phases  There are separate identified phases in the waterfall model: 1. Requirements analysis and definition. 2. System and software design. 3. Implementation and unit testing. 4. Integration and system testing. 5. Operation and maintenance. The main drawback of the waterfall model is the difficulty of accommodating change after the process is underway. In principle, a phase has to be completed before moving on to the next phase. Chapter 2 Software 11/24/2024 9 Process_Dr.asmaa  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.  In those circumstances, the plan-driven nature of the waterfall model helps coordinate the work. - The waterfall model is mostly used for large systems engineering projects where a system is developed at several sites. Chapter 2 Software 11/24/2024 10 Process_Dr.asmaa 2- Incremental development Chapter 2 Software 11/24/2024 11 Process_Dr.asmaa  Incremental development benefits 1- The cost of accommodating changing customer requirements is reduced.  The amount of analysis and documentation that has to be redone is much less than is required with the waterfall model. 2- 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. 3- 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 11/24/2024 12 Process_Dr.asmaa  Incremental development problems  The process is not visible.  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.  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 11/24/2024 13 Process_Dr.asmaa 3- Integration and configuration  Based on software reuse systems are integrated from existing components or application systems (sometimes called )COTS - Commercial-off-the-shelf) systems.  Reused elements may be configured to adapt their behavior and functionality to a user’s requirements  Reuse is now the standard approach for building many types of business system  Reuse is covered in more depth in Chapter 15. Chapter 2 Software 11/24/2024 14 Process_Dr.asmaa Types of reusable software 1. Stand-alone application systems (sometimes called COTS) that are configured for use in a particular environment. 2. Collections of objects that are developed as a package to be integrated with a component framework such as.NET or J2EE )Java 2 Platform Enterprise Edition( 3. Web services that are developed according to service standards and which are available for remote invocation. Chapter 2 Software 11/24/2024 15 Process_Dr.asmaa Key process stages 1. Requirements specification 2. Software discovery and evaluation 3. Requirements refinement 4. Application system configuration 5. Component adaptation and integration Chapter 2 Software 11/24/2024 16 Process_Dr.asmaa Advantages and disadvantages for reuse SW  Advantages  Reduced costs and risks as less software is developed from scratch  Faster delivery and deployment of system  Disadvantages  But requirements compromises are inevitable ‫غيرمتوقع‬ so system may not meet the real needs of users  Loss of control over the evolution of reused system elements Chapter 2 Software 11/24/2024 17 Process_Dr.asmaa  Process activities Chapter 2 Software 11/24/2024 18 Process_Dr.asmaa 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.  The four basic process activities of specification, development, validation and evolution are organized differently in different development processes.  For example, in the waterfall model, they are organized in sequence, whereas in incremental development they are interleaved. Chapter 2 Software 11/24/2024 19 Process_Dr.asmaa  1- Software specification  The process of establishing what services are required and the constraints on the system’s operation and development.  There are three main activities in the requirements engineering process:  Requirements elicitation and analysis‫س‬ What do the system stakeholders require or expect from the system?  Requirements specification Defining the requirements in detail  Requirements validation Checking the validity of the requirements Chapter 2 Software 11/24/2024 20 Process_Dr.asmaa 2- 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. Chapter 2 Software 11/24/2024 21 Process_Dr.asmaa A general model of the design process Chapter 2 Software 11/24/2024 22 Process_Dr.asmaa  Design activities  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. Chapter 2 Software 11/24/2024 23 Process_Dr.asmaa System implementation  The software is implemented either by developing a program or programs or by configuring an application system.  Design and implementation are interleaved activities for most types of software system.  Programming is an individual activity with no standard process.  Debugging is the activity of finding program faults and correcting these faults. Chapter 2 Software 11/24/2024 24 Process_Dr.asmaa 3- Software validation  Verification and validation (V & V) is intended to show that a system conforms to its specification and meets the requirements of the system customer.  Involves checking and review processes and system testing.  System testing involves executing the system with test cases that are derived from the specification of the real data to be processed by the system.  Testing is the most commonly used V & V activity. Chapter 2 Software 11/24/2024 25 Process_Dr.asmaa  Testing stages  Component testing  Individual components are tested independently;  Components may be functions or objects or coherent groupings of these entities.  System testing  Testing of the system as a whole. Testing of emergent properties is particularly important.  Customer testing  Testing with customer data to check that the system meets the customer’s needs. Chapter 2 Software 11/24/2024 26 Process_Dr.asmaa  Testing phases in a plan-driven software process (V-model) Figure x Testing phases in a plan-driven software process Figure x illustrates how test plans are the link between testing and development activities. This is sometimes called the V-model of development (turn it on its side to see the V). The V-model shows the software validation activities that correspond to each stage of the waterfall process model. Chapter 2 Software 11/24/2024 27 Process_Dr.asmaa 4- Software evolution  Software is inherently flexible and can change.  As requirements change through changing business circumstances, the software that supports the business must also evolve and change.  Although there has been a demarcation between development and evolution (maintenance) this is increasingly irrelevant as fewer and fewer systems are completely new. Chapter 2 Software 11/24/2024 28 Process_Dr.asmaa  Coping with change Chapter 2 Software 11/24/2024 29 Process_Dr.asmaa 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 implementations  Changing platforms require application changes  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 Chapter 2 Software 11/24/2024 30 Process_Dr.asmaa  Reducing the Costs of Rework ( self reading)  Change anticipation, where the software process includes activities that can anticipate possible changes before significant rework is required.  For example, a prototype system may be developed to show some key features of the system to customers.  Change tolerance, where the process is designed so that changes can be accommodated at relatively low cost.  This normally involves some form of incremental development. 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 be altered to incorporate the change. Chapter 2 Software 11/24/2024 31 Process_Dr.asmaa Coping with changing requirements  System prototyping, where a version of the system or part of the system is developed quickly to check the customer’s requirements and the feasibility of design decisions. This approach supports change anticipation.  Incremental delivery, where system increments are delivered to the customer for comment and experimentation. This supports both change avoidance and change tolerance. Chapter 2 Software 11/24/2024 32 Process_Dr.asmaa Software prototyping  A prototype is an initial version of a system used to demonstrate concepts and try out design options.  A prototype can be used in: 1. The requirements engineering process to help with requirements elicitation and validation; 2. In design processes to explore options and develop a UI design; 3. In the testing process to run back-to-back tests. Chapter 2 Software 11/24/2024 33 Process_Dr.asmaa Benefits of prototyping 1. Improved system usability. 2. A closer match to users’ real needs. 3. Improved design quality. 4. Improved maintainability. 5. Reduced development effort. Chapter 2 Software 11/24/2024 34 Process_Dr.asmaa The process of prototype development Chapter 2 Software 11/24/2024 35 Process_Dr.asmaa  Prototype development  May be based on rapid prototyping languages or tools  May involve leaving out functionality  Prototype should focus on areas of the product that are not well-understood;  Error checking and recovery may not be included in the prototype;  Focus on functional rather than non-functional requirements such as reliability and security Chapter 2 Software 11/24/2024 36 Process_Dr.asmaa Throw-away prototypes  Prototypes should be discarded after development as they are not a good basis for a production system: 1. It may be impossible to tune the system to meet non-functional requirements; 2. Prototypes are normally undocumented; 3. The prototype structure is usually degraded through rapid change; 4. The prototype probably will not meet normal organizational quality standards. Chapter 2 Software 11/24/2024 37 Process_Dr.asmaa  Difference Between Evolutionary Prototyping and Throw-away Prototyping Evolutionary Prototyping Model hrow-away Prototyping Model Chapter 2 Software 11/24/2024 38 Process_Dr.asmaa 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 through for later increments can continue to evolve. Chapter 2 Software 11/24/2024 39 Process_Dr.asmaa  Chapter 2 Software 11/24/2024 40 Process_Dr.asmaa  Incremental development and delivery  Incremental development  Develop the system in increments and evaluate each increment before proceeding to the development of the next increment;  Normal approach used in agile methods;  Evaluation done by user/customer proxy.  Incremental delivery  Deploy an increment for use by end-users;  More realistic evaluation about practical use of software;  Difficult to implement for replacement systems as increments have less functionality than the system being replaced. Chapter 2 Software 11/24/2024 41 Process_Dr.asmaa Incremental delivery advantages 1. Customer value can be delivered with each increment so system functionality is available earlier. 2. Early increments act as a prototype to help elicit requirements for later increments. 3. Lower risk of overall project failure. 4. The highest priority system services tend to receive the most testing. Chapter 2 Software 11/24/2024 42 Process_Dr.asmaa Incremental delivery problems  Most systems require a set of basic facilities that are used by different parts of the system.  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. ‫الصورة تتضح في النهاية‬  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. Chapter 2 Software 11/24/2024 43 Process_Dr.asmaa  Process improvement Chapter 2 Software 11/24/2024 44 Process_Dr.asmaa Process improvement  Many software companies have turned to software process improvement as a way of enhancing the quality of their software, reducing costs or accelerating their development processes.  Process improvement means understanding existing processes and changing these processes to increase product quality and/or reduce costs and development time. Chapter 2 Software 11/24/2024 45 Process_Dr.asmaa  Approaches to improvement 1- The process maturity approach, which focuses on improving process and project management and introducing good software engineering practice.  The level of process maturity reflects the extent to which good technical and management practice has been adopted in organizational software development processes.  2- The agile approach, which focuses on iterative development and the reduction of overheads in the software process.  The primary characteristics of agile methods are rapid delivery of functionality and responsiveness to changing customer requirements. Chapter 2 Software 11/24/2024 46 Process_Dr.asmaa  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. Chapter 2 Software 11/24/2024 47 Process_Dr.asmaa Process measurement  Wherever possible, quantitative process data should be collected  However, where organisations do not have clearly defined process standards this is very difficult as you don’t know what to measure. A process may have to be defined before any measurement is possible.  Process measurements should be used to assess process improvements  But this does not mean that measurements should drive the improvements. The improvement driver should be the organizational objectives. Chapter 2 Software 11/24/2024 48 Process_Dr.asmaa 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. Chapter 2 Software 11/24/2024 49 Process_Dr.asmaa  Chapter 2 Software 11/24/2024 50 Process_Dr.asmaa  Chapter 2 Software 11/24/2024 51 Process_Dr.asmaa  Chapter 2 Software 11/24/2024 52 Process_Dr.asmaa  The (Software Engineering Institute) SEI capability maturity model  Initial  Essentially uncontrolled  Managed / Repeatable  Product management procedures defined and used  Defined  Process management procedures and strategies defined and used  Quantitatively Managed  Quality management strategies defined and used  Optimizing  Process improvement strategies defined and used Chapter 2 Software 11/24/2024 53 Process_Dr.asmaa  Key points  Software processes are the activities involved in producing a software system. Software process models are abstract representations of these processes.  General process models describe the organization of software processes.  Examples of these general models include the ‘waterfall’ model, incremental development, and reuse-oriented development.  Requirements engineering is the process of developing a software specification.  Design and implementation processes are concerned with transforming a requirements specification into an executable software system.  Software validation is the process of checking that the system conforms to its specification and that it meets the real needs of the users of the system.  Software evolution takes place when you change existing software systems to meet new requirements. The software must evolve to remain useful. Chapter 2 Software 11/24/2024 54 Process_Dr.asmaa  Key points  Processes should include activities such as prototyping and incremental delivery to cope with change.  Processes may be structured for iterative development and delivery so that changes may be made without disrupting the system as a whole.  The principal approaches to process improvement are agile approaches, geared to reducing process overheads, and maturity-based approaches based on better process management and the use of good software engineering practice.  The SEI process maturity framework identifies maturity levels that essentially correspond to the use of good software engineering practice. Chapter 2 Software 11/24/2024 55 Process_Dr.asmaa