The Rational Unified Process (RUP) methodology is an example of a modern software process model that has been derived from the UML and the associated Unified Software Development Process. The RUP recognises that conventional process models present a single view of the process. In contrast, the RUP is described from three perspectives [3,11,17,22]:
1. A dynamic perspective that shows the phases of the model over time.
2. A static perspective that shows the process activities.
3. A practice perspective that suggests good practices to be used during the process.
Figure 3.6. Phases of Rational Unified Process.
The RUP (Figure 3.6.) identifies four discrete development phases in the software process that are not equated with process activities. The phases in the RUP are more closely related to business rather than technical concerns. These phases in the RUP are:
1. Inception. The goal of the inception phase is to establish a business case for the system, identify all external entities, i.e. people and systems that will interact with the system and define these interactions. Then this information is used to assess the contribution that the system makes to the business.
2. Elaboration. The goals of the elaboration phase are to develop an understanding of the problem domain, establish an architectural framework for the system, develop the project plan and identify key project risks.
3. Construction. The construction phase is essentially concerned with system design, programming and testing.
4. Transition. The final phase of the RUP is concerned with moving the system from the development community to the user community and making it work in a real environment.
Iteration within the RUP is supported in two ways. Each phase may be enacted in an iterative way with the results developed incrementally. In addition, the whole set of phases may also be enacted incrementally.
The static view of the RUP focuses on the activities that take place during the development process. These are called workflows in the RUP description. There are six core process workflows identified in the process and three core supporting workflows. The RUP has been designed in conjunction with the UML so the workflow description is oriented around associated UML models. The core engineering and support workflows are the followings:
1. Business modelling. The business processes are modelled using business use cases.
2. Requirements. Actors who interact with the system are identified and use cases are developed to model the system requirements.
3. Analysis and design. A design model is created and documented using architectural models, component models, object models and sequence models.
4. Implementation. The components in the system are implemented and structured into implementation sub-systems. Automatic code generation from design models helps accelerate this process.
5. Testing. Testing is an iterative process that is carried out in conjunction with implementation. System testing follows the completion of the implementation.
6. Deployment. A product release is created, distributed to users and installed in their workplace.
7. Configuration and change management. This supporting workflow manages changes to the system.
8. Project management. This supporting workflow manages the system development.
9. Environment. This workflow is concerned with making appropriate software tools available to the software development team.
The advantage in presenting dynamic and static views is that phases of the development process are not associated with specific workflows. In principle at least, all of the RUP workflows may be active at all stages of the process. Of course, most effort will probably be spent on workflows such as business modelling and requirements at the early phases of the process and in testing and deployment in the later phases.
The practice perspective on the RUP describes good software engineering practices that are recommended for use in systems development. Six fundamental best practices are recommended:
1. Develop software iteratively. Plan increments of the system based on customer priorities and develop and deliver the highest priority system features early in the development process.
2. Manage requirements. Explicitly document the customer’s requirements and keep track of changes to these requirements. Analyze the impact of changes on the system before accepting them.
3. Use component-based architectures. Structure the system architecture into components.
4. Visually model software. Use graphical UML models to present static and dynamic views of the software.
5. Verify software quality. Ensure that the software meets the organisational quality standards.
6. Control changes to software. Manage changes to the software using a change management system and configuration management procedures and tools.
The RUP is not a suitable process for all types of development but it does represent a new generation of generic processes. The most important innovations are the separation of phases and workflows, and the recognition that deploying software in a user’s environment is part of the process. Phases are dynamic and have goals. Workflows are static and are technical activities that are not associated with a single phase but may be used throughout the development to achieve the goals of each phase.
3.5 Exercises
1. What software development project does waterfall model recommended for?
2. What software development project does waterfall model not recommended for?
3. List application problems related to waterfall development!
4. What is the meaning of requirements validation?
5. What are the main activities of software design phase?
6. What is the different between the system and acceptance testing?
7. Explain the role of prototypes in the evolutionary development!
8. Explain the reason for software developed by an evolutionary development are often more difficult to maintain!
9. What are the support workflows in RUP?
10. How does RUP support the iterative software process?
4 Agile methods
Nowadays, most organizations and companies have to work under rapidly changing conditions. Software is used in almost all business so it is essential that new software is developed quickly. Rapid software development is therefore one of the most critical requirement for software systems [1,23].
The conventional software development processes that are based on completely specifying the requirements then designing, building and testing the system are not applicable to rapid software development. As the requirements change the system design or implementation has to be reworked and retested. As a consequence, the development process is usually late and the final software is delivered to the customer long after it was originally specified. In some cases the original reason for developing software may have changed so radically that the software becomes effectively useless when it is delivered. Therefore, development processes, especially in the case of business systems, have to focus on rapid software development and delivery.
In the 1980s and early 1990s, it was considered that the best way to achieve better software quality was provided by rigorously planned and controlled conventional software development processes that were normally used for development of large-scale systems.
These development processes usually involve a significant overhead in planning, designing and documenting the system. However, when this plan-based development approach was applied to small and medium-sized business systems, the overhead involved was so large that it sometimes dominated the software development process. Software engineers often spent more time on how the system should be developed, than on program development and testing.
Dissatisfaction with these approaches led a number of software developers in the 1990s to propose new agile methods. These allowed the development team to focus on the software itself rather than on its design and documentation. Agile methods universally rely on an iterative approach to software specification, development and delivery, and were designed primarily to support business application development where the system requirements usually changed rapidly during the development process. They are intended to deliver working software quickly to customers, who can then propose new and changed requirements to be included in later iterations of the system.
Figure 4.1. The Agile Manifesto.
In February 2001, 17 software developers met at the Snowbird, Utah resort, to discuss lightweight development methods. They published the Manifesto for Agile Software Development to define the approach now known as agile software development. The Agile Manifesto reads, in its entirety, as follows:
We are uncovering better ways of developing software by doing it and helping others do it.
Through this work we have come to value:
1. Individuals and interactions over Processes and tools 2. Working software over Comprehensive documentation 3. Customer collaboration over Contract negotiation 4. Responding to change over Following a plan
That is, while there is value in the items on the right, we value the items on the left more.
The meanings of the manifesto items on the left within the agile software development context are:
− Individuals and interactions. In agile development, self-organization and motivation are important, as are interactions like co-location and pair programming.
− Working software. Working software will be more useful and welcome than just presenting documents to clients in meetings.
− Customer collaboration. Requirements cannot be fully collected at the beginning of the software development cycle, therefore continuous customer or stakeholder involvement is very important.
− Responding to change. Agile development is focused on quick responses to change and continuous development.
The Agile Manifesto is based on twelve principles:
1. Customer satisfaction by rapid delivery of useful software.
2. Welcome changing requirements, even late in development.
3. Working software is delivered frequently (weeks rather than months).
4. Working software is the principal measure of progress.
5. Sustainable development, able to maintain a constant pace.
6. Close, daily cooperation between business people and developers.
7. Face-to-face conversation is the best form of communication (co-location).
8. Projects are built around motivated individuals, who should be trusted.
9. Continuous attention to technical excellence and good design.
10. Simplicity, the art of maximizing the amount of work not done, is essential.
11. Self-organizing teams.
12. Regular adaptation to changing circumstances.
Agile software development processes are designed to produce useful software quickly.
Generally, they are iterative processes where specification, design, development and testing are interleaved. The software is not developed and deployed in its entirety but in a series of increments, with each increment including new system functionality. Although there are many approaches to rapid software development, they share some fundamental characteristics:
1. The processes of specification, design and implementation are concurrent. There is no detailed system specification, and design documentation is minimised or generated automatically by the programming environment used to implement the system. The user requirements document defines only the most important characteristics of the system.
2. The system is developed in a series of increments. End-users and other system stakeholders are involved in specifying and evaluating each increment. They may propose changes to the software and new requirements that should be implemented in a later increment of the system.
3. System user interfaces are often developed using an interactive development system that allows the interface design to be quickly created by drawing and placing icons on the interface.
Incremental development involves producing and delivering the software in increments rather than in a single package (Figure 4.2.). Each process iteration produces a new software increment. The two main advantages to adopting an incremental approach to software development are:
1. Accelerated delivery of customer services. Early increments of the system can deliver high-priority functionality so that customers can get value from the system early in its development. Customers can see their requirements in practice and specify changes to be incorporated in later releases of the system.
2. User engagement with the system. Users of the system have to be involved in the incremental development process because they have to provide feedback to the development team on delivered increments.
Figure 4.2. Incremental development process.
However, there can be real difficulties with incremental development, particularly in large companies with fairly rigid procedures and in organisations where software development is usually outsourced to an external contractor. The major difficulties with iterative development and incremental delivery are:
1. Management problems. Software processes that are generally applied for large system development regularly generate documents that can be used to assess the progress of development. However, in an iterative development process a lots of system documentation is produced that is not cost effective. Furthermore, managers may have difficulties relating to the applied technologies and skill of staff.
2. Contractual problems. The contract between a customer and a software developer is normally based on the system specification. In the case of iterative development the complete specification is only available at the end of development, so it may be difficult to design a contract for the system development.
3. Validation problems. An independent V & V team can start work as soon as the specification is available and can prepare tests in parallel with the system implementation. However, iterative development processes interleave specification and development. Hence, independent validation of incrementally developed systems is difficult.
4. Maintenance problems. Continual change may corrupt the structure of any software system and makes it difficult to understand. This problem can be reduced by continual refactoring program codes.
Of course, there are some types of systems where incremental development and delivery is not the best approach. These are very large systems where development may involve teams
working in different locations, some embedded systems where the software depends on hardware development and some critical systems where all the requirements must be analysed to check for interactions that may compromise the safety or security of the system.
Probably the best-known agile method is extreme programming. Other agile approaches include Scrum, Crystal, Adaptive Software Development, DSDM and Feature Driven Development. Although these agile methods are all based around the notion of incremental development and delivery, they propose different processes to achieve this. However, they share a set of principles and therefore have much in common. In this chapter the Extreme Programming, Scrum and Feature Driven Development are overviewed.