Lecture 15 (1)

Software Quality Engineering BS(SE)-VI

Dr. Assad Abbas

Department of Computer Science

Topics

n Performing QA Activities

n QA and SDLC Phases

5 Waterfall, Prototyping, Spiral

Introduction…

n Why discuss the models?

n Answer: They represent the framework of a

disciplined approach to development.

5 Have milestones, deliverables, constraints, etc.

n SQA must take place in conjunction with the

completing of these activities or looking at the work products produced from these activities.

n Need to understand the models before we can

Classic and Other Software Development Methodologies

n The Software Development Life Cycle (SDLC)

n The prototyping model

n The spiral model

The SDLC

n The ‘classic model

5 Still in WIDE use today

5 Captures the major building blocks in development

5 Linear sequence

5 Highly structured; plan-driven;

5 Product delivered for evaluation and deployment at the end of development and testing

5 Used for major projects of length

Prototyping Model

n Replaces some of the parts of the SDLC with an

evolutionary and iterative process.

n Software prototypes are repeatedly provided to customer for evaluation and feedback.

5 Primarily iterate design and implementation.

5 Development teams are provided requirements.

n Ultimately, the product reaches a satisfactory completion.

Spiral Model

n Uses an iterative approach designed to address each phase

in development by obtaining customer comments and

change, risk analysis, and resolution.

n The spiral model typically has a ‘spiral’ for each of the

traditional development phases.

n Within a cycle, specific engineering (design, development,

etc.) can take place using any other models, like SDLC, prototyping,..

n The Spiral Model is a risk-centered development model

where each spiral includes major risk activities / assessments.

n Was developed after SDLC in response to delayed risk in

The Object-Oriented Model

n Emphasis here is on re-usability via reusable objects

and components.

n Component-based software development.

n For non-available components, developer may

5 prototype needed modules,

5 use an SDLC approach,

The SDLC

• Requirements

Definition: done by customers.

• Analysis: analyze

requirements to form an initial software model.

• Design: Detailed

The SDLC

• Coding: Design

translated into code.

• Coding includes SQA activities such as

inspections, unit tests and integration tests.

• Many takeoffs from this: These tests done by

The SDLC

• System Tests: Goal: to discover errors / correct errors to achieve an

acceptable level of

quality. Carried out by developers prior to

delivery.

• Sometimes ‘acceptance tests’ carried out by

The SDLC

• Installation / Conversion:

• After testing, system is installed and/or replaces an existing system.

• Requires software / data conversion.

• Important to not interrupt daily activities during

conversion process.

The SDLC

• Operations and Maintenance:

• Hopefully done for years.

• Maintenance:

• Corrective

• Adaptive

• Perfective

• Lots of variations to the classic SDLC many in response to problems….

The Prototyping Model

n One main idea behind prototyping is for the

development of fast prototypes and customer

availability for feedback.

n Often prototyping tools are used to help.

n Developers respond to feedback and add

additional parts as application evolves into an acceptable product.

n Recognize this process can be inserted into

The Prototyping Model

ACCEPTANCE TESTS

Prototyping Model - more

n Advantages

5 Shorter development process.

5 Substantial savings in development resources (time).

5 _{Better fit to customer requirements and reduced risk}

of project failure.

5 Easier and faster user comprehension of new system.

n Disadvantages

The Spiral Model

n A heavy-weight, plan-driven, highly-structured

approach for large projects.

n Especially designed for those with higher chances of

failure.

n Combines iterative model, emphasizes risk

assessment, customer participation, prototyping, and more

The Spiral Model

Each spiral includes:

• _Planning

• Risk Analysis / Resolution

• Engineering activities (design, code, test…)

• _{Customer Evaluation}

The Advanced Spiral Model-The Win-Win Model

Revised Spiral Model provides

customer with improved chances for changes;

developer better chances to stay within budget and time.

Done by increased emphasis on customer participation and on engineering activities.

Extra sections in spiral

dedicated to customer actions

The Object-Oriented Model

n Easy integration of existing software modules (objects / components)

into newly developed software systems.

n Process begins with OOA and OOD.

n Then, acquire suitable components from reusable software component

libraries (or purchase them).

n Otherwise, develop as needed.

n Can involve adding to repertoire of library components.

n Economy: integrating reusable components; much lower cost than

developing.

n Improved quality – using tested components

n Shorter development times: integration of reusable software

Factors affecting intensity of quality assurance activities in the development projects

n Quality assurance activities will be integrated into

development plan that implements one or more SW development models.

n Quality assurance planners for project are required to

determine :

5 The list of QA activities needed for a project

5 For each QA activity:

g Timing

g Who to perform & the resources required g Team members, external body for QA

Factors affecting intensity of quality assurance activities in the development projects…

n Project factors

5 Magnitude of the project

5 Technical complexity and difficulty

5 Extent of reusable SW components

5 Severity of failure outcome if the project fails

n Team factors

5 Professional qualification of team members

5 Team acquaintance with the project and its experience in the area

How project and team factors can

Example 1

n A software development team has planned the quality

assurance activities for its new consumer club project.

The current project contract, signed with a leading furniture store, is the team’s 11th consumer club project dealing in the last three years. The team

estimates that about seven man-months need to be

invested by the two team members assigned to the

Example 1…

n The main considerations affecting this plan are:

5 Degree of team acquaintance with the subject

5 High percentage of software reuse

Example 2

n The real-time software development unit of a hospital’s information

systems department has been assigned to develop an advanced patient

monitoring system. The new monitoring unit is to combine patient’s room unit with a control unit. The patient’s room unit is meant to interface with several types of medical equipment, supplied by different manufacturers, which measure various indicators of the patient’s condition. A

sophisticated control unit will be placed at the nurses’ station, with data to be communicated to cellular units carried by doctors.

n The project leader estimates that 14 months will be required to complete

the system; a team of five will be needed, with an investment of a total of

n The main considerations

affecting this plan are:

5 High complexity and difficulty of the system.

5 Low percentage of reusable software available.

5 Large size of the project.

5 High severity of failure

Exercise 2

References

1. Software Quality Assurance: from Theory to