Software Processes PDF

Chapter 2 Software Processes 11/24/2024 Chapter 2 Software Processes 1 Topics covered  Software process models  Process activities  Coping with change  Process improvement 11/24/2024 Chapter 2 Software Processes 2  The software process  A structured...

Chapter 2 Software Processes 11/24/2024 Chapter 2 Software Processes 1 Topics covered  Software process models  Process activities  Coping with change  Process improvement 11/24/2024 Chapter 2 Software Processes 2  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. 11/24/2024 Chapter 2 Software Processes 3  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 models describing the architecture have been reviewed. 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.  In 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. 11/24/2024 Chapter 2 Software Processes 5  Software process models 11/24/2024 Chapter 2 Software Processes 6  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. 11/24/2024 Chapter 2 Software Processes 7 1- The waterfall model 11/24/2024 Chapter 2 Software Processes 8  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. 11/24/2024 Chapter 2 Software Processes 9  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. 11/24/2024 Chapter 2 Software Processes 10 2- Incremental development 11/24/2024 Chapter 2 Software Processes 11  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. 11/24/2024 Chapter 2 Software Processes 12  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. 11/24/2024 Chapter 2 Software Processes 13 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. 11/24/2024 Chapter 2 Software Processes 14 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. 11/24/2024 Chapter 2 Software Processes 15 Key process stages 1. Requirements specification 2. Software discovery and evaluation 3. Requirements refinement 4. Application system configuration 5. Component adaptation and integration 11/24/2024 Chapter 2 Software Processes 16 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 11/24/2024 Chapter 2 Software Processes 17  Process activities 30/10/2014 Chapter 2 Software Processes 18 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. 11/24/2024 Chapter 2 Software Processes 19  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 analysis 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 11/24/2024 Chapter 2 Software Processes 20 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. 11/24/2024 Chapter 2 Software Processes 21 A general model of the design process 11/24/2024 Chapter 2 Software Processes 22  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. 11/24/2024 Chapter 2 Software Processes 23 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. 11/24/2024 Chapter 2 Software Processes 24 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. 11/24/2024 Chapter 2 Software Processes 25  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. 11/24/2024 Chapter 2 Software Processes 26  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. 11/24/2024 Chapter 2 Software Processes 27 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. 11/24/2024 Chapter 2 Software Processes 28  Coping with change 11/24/2024 Chapter 2 Software Processes 29 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 11/24/2024 Chapter 2 Software Processes 30  Reducing the costs of rework  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. 11/24/2024 Chapter 2 Software Processes 31 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. 11/24/2024 Chapter 2 Software Processes 32 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. 11/24/2024 Chapter 2 Software Processes 33 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. 11/24/2024 Chapter 2 Software Processes 34 The process of prototype development 11/24/2024 Chapter 2 Software Processes 35  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 11/24/2024 Chapter 2 Software Processes 36 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. 11/24/2024 Chapter 2 Software Processes 37  Difference Between Evolutionary Prototyping and Throw-away Prototyping Evolutionary Prototyping Model hrow-away Prototyping Model 11/24/2024 Chapter 2 Software Processes 38 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 requirements for later increments can continue to evolve. 11/24/2024 Chapter 2 Software Processes 39 11/24/2024 Chapter 2 Software Processes 40  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. 11/24/2024 Chapter 2 Software Processes 41 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. 11/24/2024 Chapter 2 Software Processes 42 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.  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. 11/24/2024 Chapter 2 Software Processes 43  Process improvement 11/24/2024 Chapter 2 Software Processes 44 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. 11/24/2024 Chapter 2 Software Processes 45  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. 11/24/2024 Chapter 2 Software Processes 46  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. 11/24/2024 Chapter 2 Software Processes 47 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. 11/24/2024 Chapter 2 Software Processes 48 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. 11/24/2024 Chapter 2 Software Processes 49 11/24/2024 Chapter 2 Software Processes 50 11/24/2024 Chapter 2 Software Processes 51 11/24/2024 Chapter 2 Software Processes 52  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 11/24/2024 Chapter 2 Software Processes 53  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. 11/24/2024 Chapter 2 Software Processes 54  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. 11/24/2024 Chapter 2 Software Processes 55