Chapter 2

Question 1

What is the software process / model?
Write also what they involve.

Answer 1

A structured set of activities required to develop a software system.

A software process model is an abstract representation of a process. It presents a description of a process from some particular perspective.

Many different software processes but all involve:
▪ Specification – defining what the system should do;
▪ Design and implementation – defining the organization of the system and implementing the system;
▪ Validation – checking that it does what the customer wants;
▪ Evolution – changing the system in response to changing customer needs.

Question 2

What can you tell about software process descriptions?

Answer 2

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:
▪ Products, which are the outcomes of a process activity;
▪ Roles, which reflect the responsibilities of the people involved in the process;
▪ Pre- and post-conditions, which are statements that are true before and after a process activity has been enacted or a product produced.

Question 3

What is a Plan-Driven Process?

Answer 3

Plan-driven processes are processes where all of the process activities are planned in advance and progress is measured against this plan.

Question 4

What is an Agile Process?

Answer 4

In agile processes, planning is incremental and it is easier to change the process to reflect changing customer requirements.

Question 5

Talk about the Waterfall Model. Draw a schema.

Answer 5

Plan-driven model. Separate and distinct phases of specification and development.

There are separate identified phases in the waterfall model:
▪ Requirements analysis and definition
▪ System and software design
▪ Implementation and unit testing
▪ Integration and system testing
▪ 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 complete before moving onto the next phase.

Question 6

What are the Waterfall Model Problems?

Answer 6

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.
 The waterfall model is mostly used for large systems engineering projects where a system is developed at several sites.
▪ In those circumstances, the plan-driven nature of the waterfall model helps coordinate the work.

Question 7

Write a description about the process of the waterfall model.

Answer 7

First, the systems’ goals are established. Then, we establish an overall system architecture. Then, we verify if each unit meets its specifications, while implementing the software design. After that, the programs are tested as a complete system, to ensure that the requirements are met. Finally, the system is installed and put into practical use, correcting errors.

Question 8

Talk about the Incremental Development Model and its benefits. Draw a schema.

Answer 8

May be plan-driven or agile. Specification, development and validation are interleaved.

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.

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.

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.

Question 9

Talk about the Incremental Development Model Problems.

Answer 9

The process is not visible.
▪ Managers need regular deliverables to measure progress. Rapid system development makes it impractical to document every version.

System structure tends to degrade as new increments are added.

Question 10

What is the Reuse-Oriented Software Engineering? Write its stages.

Answer 10

Based on systematic reuse where systems are integrated from existing components or COTS (Commercial-off-the-shelf) systems.
Reuse is now the standard approach for building many types of business system.

Process stages
▪ Component analysis;
▪ Requirements modification;
▪ System design with reuse;
▪ Development and integration.

Question 11

What are the types of software component?

Answer 11

Web services that are developed according to service standards and which are available for remote invocation.

Collections of objects that are developed as a package to be integrated with a component framework such as .NET or J2EE.

Stand-alone software systems (COTS) that are configured for use in a particular environment.

Question 12

What is software specification?

Answer 12

The process of establishing what services are required and the constraints on the system’s operation and development.

Requirements engineering process:
Feasibility study
* Is it technically and financially feasible to build the system?

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

Question 13

Talk about software design and implementation.

Answer 13

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

Software design
▪ Design a software structure that realizes the specification;

Implementation
▪ Translate this structure into an executable program;

The activities of design and implementation are closely related and may be inter-leaved.

Question 14

What are some design activities?

Answer 14

Architectural design, where you identify the overall structure of the system, the principal components (sometimes called sub-systems or modules), their
relationships and how they are distributed.

Interface design, where you define the interfaces between system components.

Component design, where you take each system component and design how it will operate.

Database design, where you design the system data structures and how these are to be represented in a database.

Question 15

What can you say about software validation?

Answer 15

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.

Question 16

What are the testing stages?

Answer 16

Development or 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.

Acceptance testing
▪ Testing with customer data to check that the system meets the customer’s needs.

Question 17

How can we reduce the costs of rework?

Answer 17

Change avoidance, where the software process includes activities that can anticipate possible changes before
significant rework is required.

Change tolerance, where the process is designed so that changes can be accommodated at relatively low cost.

Question 18

What can you write about software prototyping? Write also the benefits.

Answer 18

A prototype is an initial version of a system used to demonstrate concepts and try out design options.
 A prototype can be used in:
▪ The requirements engineering process to help with requirements elicitation and validation;
▪ In design processes to explore options and develop a UI design;
▪ In the testing process to run back-to-back tests.

Benefits:
 Improved system usability.
 A closer match to users’ real needs.
 Improved design quality.
 Improved maintainability.
 Reduced development effort.

Question 19

What can you say about the prototype development?

Answer 19

 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

Question 20

What can you say about throw-away prototypes?

Answer 20

Prototypes should be discarded after development as they are not a good basis for a production system:
▪ It may be impossible to tune the system to meet non-functional requirements;
▪ Prototypes are normally undocumented;
▪ The prototype structure is usually degraded through rapid change;
▪ The prototype probably will not meet normal organizational quality standards.

Question 21

What is Incremental Delivery?

Answer 21

 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 prioritized and the highest priority requirements are included in early increments.

 Once the development of an increment is started, the requirements are frozen though requirements for later increments can continue to evolve.

Question 22

Incremental Development vs. Incremental Delivery

Answer 22

 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.

Question 23

Write the Incremental Delivery advantages:

Answer 23

 Customer value can be delivered with each increment so system functionality is available earlier.
 Early increments act as a prototype to help elicit requirements for later increments.
 Lower risk of overall project failure.
 The highest priority system services tend to receive the most testing.

Question 24

Write the Incremental Delivery Problems.

Answer 24

 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.

Question 25

Write about the Boehm’s Spiral Model.

Answer 25

 Process is represented as a spiral rather than as a sequence of activities with backtracking.
 Each loop in the spiral represents a phase in the process.
 No fixed phases such as specification or design - loops in the spiral are chosen depending on what is required.
 Risks are explicitly assessed and resolved throughout the process.

Question 26

Write about the spiral model sectors.

Answer 26

 Objective setting
▪ Specific objectives for the phase are identified.

 Risk assessment and reduction
▪ Risks are assessed and activities put in place to reduce the key risks.

 Development and validation
▪ A development model for the system is chosen which can be any of the generic models.

 Planning
▪ The project is reviewed and the next phase of the spiral is planned.

Question 27

Write shortly about the spiral model usage.

Answer 27

 Spiral model has been very influential in helping people think about iteration in software processes and introducing the risk-driven approach to development.

 In practice, however, the model is rarely used as published for practical software development.