Even tho there are many different types of software systems(as introduced in chap1), and there is no universal process that can be applied to all of them, the right process depends on:

• customer and regulatory requirements
• environment where the software will be used
• type of software being developed

they all must include in some form the four fundamental activities of software engineering: specification, design implementation, validation and evolution.

Its also important to describe what is produced, who is involved and conditions that influence the sequence of activities:

1. Product: outcome of the process activity.
2. Roles: people involved in the process activity.
3. Pre- and post-conditions: conditions that must be satisfied before and after the process activity.

Software processes categories:

Plan-driven processes	Agile processes
All of the process activities are planned in advance	Planning is incremental
Progress is measured against the plan	Easier to change the process to reflect changing customer requirements
Process activities are performed in a fixed sequence	Process activities are performed in a flexible sequence

Software Process Modules

Its an abstract representation of a process. it presents a descreption of the process from some particular perspective.

Generic Process Modules

The waterfall model

Plan-driven model. This approach separates the process into distinct phases, each of which is completed before the next phase begins.

Benefits	Drawbacks	Applicability
Clear and seperate phases	Difficut to change requirements	Well-defined requirements
		No feedback from the customer.	Changes are limited during the design process
			Large systems
			Embedded systems
			Critical systems

Incremental development

This approach interleaves the process activities of specification, design, implementation and validation. The system is developed as a series of versions, with each version adding new functionality to the previous version. Could be plan-driven or agile.

Benefits	Drawbacks	Applicability
Reduce cost of changes	Invisible process, need regular deliveables to measure progress	Clear requirements
Early feedback from the customer	System structure degrade as new increments are added	Product needs to be delivered quickly
Fast software delivery & deployment		New tech is being used

Integration and configuration

This approach relies on the availability of reusable components or systems. The system development focuses on configuring these components for use in the new setting and integrating them into a system. Could be plan-driven or agile.

Type of reuseable software:

• Stand-alone application systems – COTS (Commercial Off-The-Shelf)
• Objects collection - .NET, Java Spring framework, React, etc.
• Web service that provides remote invocation - REST API, SOAP, etc.

Benefits	Drawbacks
Reduse costs and risks	System may not meet the customer’s requirements
Faster delivery	Lost control on evolution of reused software

Process Activities

Specification

Two things are established in this process:

1. What services are required?
2. What are the constraints on the system?

Requirements engineering

• To produce an agreed requirements document that specifis a system satisfying stakeholder(owner) requirements.

• Presented at two levels of detail:
  1. End-users and customers - high level statements of the requirements. (abstract)
  2. System developers - detailed system specifications.(logical)
• The RE process has 4 main activities:
  1. Feasibility study
     • Can the identified user needs may be satisfied using current software and hardware technologies?
     • Will the proposed system will be cost-effective from a business point of view?
     • Can the proposed system develop within existing budgetary constraints?
     • Should we develop the proposed system?
  2. Requirements elicitation and analysis - delivering the system requirements through observation of existing systems, discussions with potential users and so on. May involve the develpoment of one or more system models and prototypes to help you understand the system to be specified.
  3. Requirements specification - translating the info gathered during the Requirements Elicitation and Analysis activity into a document that defines a set of requirements. two types: end-user requirements and system requirements.
  4. Requirements validation - checks the requirements for realism, consistency and completeness. erroes in the requirements document discovered and corrected.

Design and implementation

The process of converting the system specification into an executable system.

• Design, designing a software structure that realizes the specification.
• Implementation, translating the design into an executable program. These two are closely related and may be interleaved(meaning that they may be performed in parallel).

A general model of the design process:

• Platform information - most software interfaces with othe software systems, these other systems include operating systems, databases, middleware, etc. These make up the “Software Platform”. environment in which the software will execute. Information about the platform is needed for designers to decide how to best integrate the software with its environment.

Design Activities:

• Architectural design - identify the overall structure of the system. the principal components and how they relate to each other.
• Database design - design the system data structure and how these are represented in a database.
• Interface design - design the interface between system components. must be unambiguous.
• Component selection and design - searching for reusable components and designing new components.

System implementation:

• By developing a program(s) or configuring an application system.
• Design and implementation are interleaved for most systems.
• Programming is an individual activity with no standard process.
• Debugging is the process of finding and correcting errors in the program.

Validation

Verification and validation (V & V) : 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.
• 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.

Stages of testing:

1. Component testing - testing of individual components independently. components may be functions, objects or coherent grouping of theseb entities.
2. System testing - testing the system as a whole
3. Customer acceptance testing - testing the system in the real environment.

Evolution

As requirements change through changing business circumstances, the software that supports the business must also evolve and change.

Coping with Change

Chnage is inevitable in large software projects because:

• Business changes lead to new and changed requirements.
• New technologies are introduced.
• Changing platforms.

Change leads to rewor(work that has been completed has to be redone), Cost of change = cost of rework(e.g. re-analysing requirements) + cost of implementing new functionality.

To reduce cost of rework:

• Change anticipation - anticipate(predict) the need for change and plan for it. e.g Prototyping
• Change tolerance - the process is designed so changes can be accommodated at relatively low cost.. e.g. incremental development

Two ways of coping with change and changing system requirements:

• System prototyping - a version of the system or part of the system is developed quickly to check the customers requirements and the feasibility of design decisions. supports change anticipation.
• Incremental delivery - system increments are delivered to the customer for comment and experimentation. supports change tolerance and change avoidance(efers to the practice of minimizing the need for changes in the first place.).

Process Improvement

A way of enhancing the quality of software, reducing costs or accelerating the development process. understands the existing processes and changing these proceses to increase product quality and reduce costs and development time.

Approaches to process improvement: | | The process maturity approach | The agile approach — | — | — Focuses | improving process and project management. | Iterative development | | introducing good software engineering practice. | The reduction of overhead in the software process Description | The level of process maturity reflects the extent to which good technical and management practice has been adopted in organizational software development processes. | The primary characteristics of agile methods are rapid delivery of functionality and responsiveness to changing customer requirements.

The process improvment cycle:

1. Measurement - measure one or more attributes of the process or product, this forms a baseline to decide whether the process improvement has been successful.
2. Analysis - the current process is assessed, and process weaknesses and bottlenecks are identified.
3. Change - Address some of the identified process weaknesses. when the changes are made, the cycle repeats to collect data about the effectiveness of the changes.

Process maturity models:(levels)

1. Initial - processes unpredictable, chaotic, ad hoc, no documentation, no process improvement.
2. Repeatable - processes are characterized for the project and often reactive.
3. Defined - processes characterized for the project and proactive.
4. Quantitatively managed - processes measured and controlled.
5. Optimizing - focus on process improvement.