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Modelling the Process and Life Cycle

Software development usually involves the following stages:

• Requirements analysis and definition• System design• Program design• Program implementation (writing the program)• Unit testing• Integration testing• System testing• System delivery• Maintenance

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What is a process?

• A series of steps involving activities, constraints and resources that produce an intended output of some kind

• Characteristics of a process:– prescribes all of the major process activities– uses resources, subject to a set of constraints (such as a

schedule), and produces intermediate and final results– may be composed of sub-processes that are linked in some

way.– each process activity has an entry and exit criteria, so we

know when each activity begins and ends

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What is a process? (continued)

– activities are organised in a sequence, so that it is clear when one activity is performed relative to the other activities

– a set of guiding principles that explain the goals of each activity

– constraints or controls may apply to an activity, resource or product.

• e.g. budget or schedule may constrain length of time activity may take

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Reasons for modelling a process• Common understanding of the activities, resources and

constraints

• Helps in the finding of inconsistencies, redundancies and omissions

• Help evaluate candidate activities for their appropriateness in meeting the goals, such as building high-quality software.

• Every process should be tailored for the special situation in which it will be used. Building a model helps the team understand where that tailoring is to occur

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Waterfall model

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Waterfall model: advantages • Very useful in helping developers layout

(very high-level view) what they need to do• Simplicity – makes it easy to explain to

customers (who are not familiar with software developers)– Explicitly states which intermediate products are

necessary in order to begin next stage

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Waterfall model: disadvantages • Failure to treat software as a problem solving

process. Software is a creation process not a manufacturing process. Software evolves as the problem is understood and the alternatives are evaluated.

In particular, creation involves trying a little of this or that, developing and evaluating prototypes, assessing the feasibility of requirements, contrasting several designs, learning from failure and eventually settling on a satisfactory solution to the problem

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Waterfall model: disadvantages

• It provides no guidance of how each activity transforms one artefact into another, such as requirements to design. Thus the model provides no guidance to managers and developers on how to handle changes to products and activities that are likely to occur during development.

If requirements change during coding, what changes do we make to design and code?

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Software development in reality

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Process models

The software development process can help control the thrashing by including activities and sub-processes that enhance understanding.

Prototyping is such a sub-process; a prototype is a partially developed product that enables customers and developers to examine some aspect of the proposed system and decide it is suitable or appropriate for the finished product.

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Prototyping model

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Prototyping model

Prototyping can be the basis of an effective process model. This model allows all or part of the system to be constructed quickly to understand or clarify issues.

The overall goal is to reduce risk and uncertainty in development.

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Phased development model

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Phased development model

This is used to reduce cycle time. The system is designed so that it can be delivered in pieces, enabling users to have some functionality while the rest is being developed. There are usually two systems functioning in parallel: the production system and the development system

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Incremental model

In the incremental model, the system as specified in the requirements is partitioned into sub-systems by functionality. The releases are defined by beginning with one small functional sub-system and then adding functionality with each new release.

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Iterative model

This model delivers a full system at the very beginning and then changes the functionality of each sub-system with each new release.

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Phased development: advantages

• Training can begin on an early release. The training process allows developers to observe how certain functions are executed, suggesting enhancements for later releases.

In this way, the developers can be very responsive to the users

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Phased development: advantages

• Markets can be created early for functionality that has never before been offered

• Frequent releases allow developers to fix unanticipated problems as they are reported

• The development team can focus on different areas of expertise with different releases.

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Question

Should a development organisation adopt a single process model for all of its software development? Discuss the pros and cons.

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AnswerPros:• Standardization of training, terminology, the

collection of process metrics, planning and estimation. Works well if the projects are very similar in nature.

Cons:• Adopting a single standard process may

unnecessarily constrain some projects from using the process that is best suited to the problem and the solution.

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Question

Suppose your contract with the customer specifies that you use a particular software development process. How can work be monitored to enforce the use of this process?

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AnswerConformance to a particular process is often checked with the use of milestones. That is, the process is defined in such a way that there are tangible products in the process whose existence indicates that particular process steps have been carried out.

For example, when using the waterfall process. These intermediate products, or milestones, could be a requirements document, a design document, the code itself, test documents etc. The timing of these products indicate whether or not the process was being followed as planned.

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Answer (continued)

Another way to monitor use of a process is by measuring effort. Developers working on the project could be required to report the effort they spent on different process activities. By tracking when effort is spent on which activities, progress through the steps of the process could be monitored.

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The Rational Unified Process

•a process framework that can be adapted and extended to suit the needs of an adopting organization.•general and comprehensive enough to be used "as is," i.e., out-of-the-box, by many small-to-medium software development organizations, especially those that do not have a very strong process culture.

From an article by Philippe Kruchten(check course webpage)

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The Rational Unified Process•Can also modify, adjust, and expand the RUP to accommodate the specific needs, characteristics, constraints, and history of its organization, culture, and domain.

•Process should not be followed blindly, generating useless work and producing artefacts that are of little added value. •Instead, must be made as lean as possible while still fulfilling its mission to help developers rapidly produce predictably high-quality software.

From an article by Philippe Kruchten(check course webpage)

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The RUP Captures Software Development Best Practices

•RUP captures many of modern software development's best practices in a form suitable for a wide range of projects and organizations:

– Develop software iteratively.– Manage requirements.– Use component-based architectures.– Visually model software.– Continuously verify software quality.– Control changes to software.

From an article by Philippe Kruchten(check course webpage)

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Develop Software Iteratively

•Most software teams still use a waterfall process for development projects, completing in strict sequence the phases of requirement analysis, design, implementation/integration, and test.

– idles key team members for extended periods

– defers testing until the end of the project lifecycle, when problems tend to be tough and expensive to resolve

– pose a serious threat to release deadlines

•By contrast, RUP represents an iterative approach that is superior

From an article by Philippe Kruchten(check course webpage)

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Manage Requirements

Requirements management is a systematic approach to eliciting, organising, communicating, and managing the changing requirements of a software-intensive system or application.

From an article by Philippe Kruchten(check course webpage)

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Continuously Verify Quality

•There is no worker in charge of quality in the RUP– Because quality is not added to a product by a few people.

•Instead, quality is the responsibility of every member of the development organization.•In software development, our concern about quality is focused on two areas:

– product quality – process quality.

From an article by Philippe Kruchten(check course webpage)

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Continuously Verify Quality (continued)

• Product quality -- The quality of the principal product being produced (the software or system) and all the elements it comprises (for example, components, subsystems, architecture, and so on).

• Process quality -- The degree to which an acceptable process (including measurements and criteria for quality) was implemented and adhered to during the manufacturing of the product.

From an article by Philippe Kruchten(check course webpage)

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Rational Unified Process

From an article by Philippe Kruchten(check course webpage)

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From an article by Philippe Kruchten (check course webpage)

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Agile Methods• Agile manifesto focuses on four simple

value statements, which defines preferences:– Individuals and interactions over processes and

tools– Working software over comprehensive

documentation– Customer collaboration over contract

negotiation– Respond to changes over following a plan

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Agile Processes

• Extreme Programming(XP)

• Crystal

• Scrum

• Adaptive Software Development

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Extreme Programming(XP)

• Leveraging the creativity of developers and minimising the amount of administration overhead

• Emphasises four characteristics of agility:– Communication– Simplicity– Courage– Feedback

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XP (continued)

• Communication– Continual interchange between customers and developers

• Simplicity– Encourages developers to select the simplest design or

implementation to address the needs of the customer

• Courage– Commitment to delivering functionality early and often

• Feedback– Loops are built into various activities during

development process

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Crystal

• Collection of approaches based on the notion that every project needs a different set of policies, conventions and methodologies

• Suggests the following:– quality of the projects and processes improves as the

quality of the people involved improves

– Productivity increases through better communication and frequent delivery because there is less need for intermediate products

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Scrum

• Uses iterative development, where each 30-day iteration is called a “sprint”

• During a “sprint”, implement the product’s backlog of prioritised requirements

• Multiple self-organising and autonomous teams implement product increments in parallel

• Coordination is done at a brief daily status meeting called a “scrum”

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Adaptive Software Development

• has six basic principles:• A mission that acts as a guideline• Features are viewed as the crucial point of the

customer value• Iteration is important• Change is embraced• Fixed delivery times• Risk is embraced

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ASD (continued)

• A mission that acts as a guideline– setting out the destination but not prescribing how to

get there

• Features are viewed as the crucial point of the customer value– so the project is organised around building components

to provide features

• Iteration is important– so redoing is as critical as doing

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ASD (continued)

• Change is embraced– so that change is viewed not as a correction but as an

adjustment to the realities of software development

• Fixed delivery times– force the developers to scope down the requirements

essential for each version produced

• Risk is embraced– so that the developer tackles the hardest problems first