the software engineering process and the personal software process (psp)

The Software Engineering Process

andThe Personal Software

Process(PSP)

The Software Engineering Process

• The Software Product• The Software Process• The Traditional Approach (SDLC)• Software Process Models• SP Modeling – why, what, how• OO Modeling - UML• Software Process Measurement• Software Process Maturity Model (CMM)• The Personal Software Process (PSP)• Appendix – Application Domains

Software Engineering Products and Processes

The software customer wants quality software products at reasonable prices

The software producer wantsa well managed software production process that consistently produces quality software in a cost-effective manner

Some organisations have a defined and managed software engineering process

The Software Product

Composed of programs, data and documents

Delivers hardware computing potential Delivers information

Software Product Characteristics»developed or engineered,

not manufactured»doesn’t wear out»most is custom built

The Software Process

• The software product is created as part of the Software Engineering Process

Definition:– the Software Process is a

description of the process which guides the software engineers as they work

The Software Process

The set of activities which produce a software product

The sequence of steps to develop and maintain software

Sets out the technical and management framework for applying methods, tools and people to the software task

The Software Process ...Software Engineering is a

Layered Technology (Diagram Pressman p.21):

Quality Focus - bedrock of SE» commitment to quality

Process – foundation of SE» framework of key processes as: a basis for control of

projects; and a context for development & methods

Methods – set of basic SE principles» technical ‘how to’ for building software, including

methods for analysis, design, programming, testing etc.

Tools – ideal is an integrated SE environment» automated support for the process and the methods

The Software Process ...

There is no ‘right’ or ‘wrong’ software process.

But poor processes reduce the quality or usefulness of the product

Software processes are complex and involve a large number of activities


Generic Phases (Pressman) Definition Phase focuses on ‘what’

- the methods will include these tasks:» system or information engineering» software project planning» requirements analysis

Development Phase focuses on ‘how’- the methods will include these tasks:

» software design» code generation» software testing

Maintenance Phase focuses on the change of the software due to correction, evolution & improvement.


Has a common process framework containing (Diagram Pressman p.24):

framework activities - for all software projects work tasks project milestones software work products and deliverables quality assurance points

umbrella activities - occur throughout the process

software quality assurance software configuration management software metrics or measurement


To solve SE problems a team of software engineers develops a strategy that includes the process, methods and tool layers, and the generic phases.

This strategy is called a Software Process Model

The process model is based on the nature of the application, & the methods, tools and deliverables.

Traditional ModelSoftware Development Life Cycle (SDLC) (Waterfall or Linear Sequential Model)

SDLC Phases:

1. System Feasibility» Aims to establish the technological, economic, social

feasibility of the proposed system.

2. Software Requirements» Requirements are the functions and features of software

desired by the customer.» Requirements are validated by obtaining the customer's

agreement to the specs.

3. Software Plans» Software planning is concerned with How much, How long?

What resources and skills will be needed? When? Estimating, scheduling, budgeting.

SDLC Phases ...

4. Product Design & Detailed Design

»Concerned with how to meet the requirements.

»Design documents are verified - checked against requirements

5. Coding and Module Testing»Programming, implementation »Producing operational models»Testing them

SDLC Phases ...

6. Integration Testing»Testing the whole product

7. Implementation»Put into operation for the first time. »Create data files / databases, user training,»Parallel running, acceptance testing.

8. Operation & Maintenance»As we have seen, covers many different

activities!

Deficiencies in the Traditional Model

Gross oversimplification In reality phases are not clear-cut. Defects in the products of earlier phases are

discovered in later phases.Best approach is an iterative one which feeds the defect information back to the earlier phase.

Documenting is a nightmare - detection of a design fault during coding - do we go back and revise the design documents? Or are they an historical artifact?

SDLC - the reality

Overlapping phases Large, complex systems are usually

broken into subsystems and other smaller components

Each subsystem may have its own mini-lifecycle.

In reality there will be a continuous stream of change requests.

Software Process Models1. Linear Sequential or ‘Waterfall’ Model

2. Prototyping Model 3. Rapid Application Development Model 4. Evolutionary Development:

Incremental Model Spiral Model Concurrent Development Model

5. Component-Based Development Model6. Formal Methods Model7. Fourth Generation Techniques Model8. Extreme Programming Model

Software Process Models ...

• Component-Based Development Model– OO technologies provide the framework – Focus is on the reuse of components (Classes)

– The Unified Software Development Process is the main component-based development model

• The Unified Development Model (UML)Unified Development Model (UML) is the notation used to define the system components

• Fourth Generation Techniques Model– When coupled with UML may become the dominant

approach to software development.

Software Process Models ...

Process TechnologyThe process models

• have different strengths and weaknesses• are adapted for use by each particular project team• are aided by process technology tools

Process Technology Tools allow:– Organisations to build automated models of the process– Team monitoring and control of the SE tasks – Each team member to plan individual project tasks

Software Process Modeling

Software Process Modeling Requirements

1. Why? - do we need to model software processes and their components?

2. What? - aspects and objects of the software process do we need to model?

3. How? - are we going to model them?

SP Modeling - Why?

The over-riding purpose The over-riding purpose

of software process modelingof software process modeling

isis

software process software process

understanding and understanding and management.management.

SP Modeling - Why?...

• Modeling levels- to allow a general view as well as a more

detailed view of the process- to allow for refinement, explosion,

elaboration- to allow managers to see the woods as

well as the trees

• Flexibility- to allow for model flexibility and

extensibility

SP Modeling - Why?...

Enaction - to allow both project managers and

developers to use the models, supported in a computer-aided manner.

Metrication (measurement)‘You cannot control what you cannot

measure’- Tom de Marco

SP Modeling - What?

Products» Important to model requirements and

design documents - the evolving product;»Products can be measured - size,

complexity, quality...

Activities»Consume resources and lead to the

development of products

SP Modeling - What? ...

Events » Important occurrences on the project time-line.»e.g.

Project start; Approval to produce a detailed proposal; Requirements acceptance;

Decisions»Branch points in the software process»e.g.

Undertake prototyping to reduce risk of inadequate requirements.

SP Modeling

How?»More advanced topic» In practice most companies select and

customise a model, supported by a CASE tool

Software Process SelectionIssues affecting process selection are related to the particular application domain

Some Application Domains(refer Appendix)

• Data-centred systems• Real-time systems• Systems programs• Life/mission-critical systems• Scientific/engineering systems• Spatial information systems (GIS)• Knowledge-based systems• Networks/data comms including intranet,

internet, WAN, LAN, e-commerce• Other including CAD/CAM, office automation

OO Modeling Concepts Static Model – the Class Diagram or Class Chart

» Classes showing specification by class contract

» Grouping into clusters/subsystems

» Relations: client/supplier and inheritance - fundamental

Dynamic models

» Identification of events

» Scenarios of communicating objects

» State charts for more dynamic parts of the system

Unified Modeling Language (UML)

is the international standard

Software Process Measurement

or Software Process Metrics– the gathering of quantitative data about

the software process– does not measure the product quality

Classes or types of Process Metrics– time taken for the process to be completed– resources required for a particular process– the number of occurrences of a particular event

Software Process Maturity

Measurement

The model to measure the maturity of an organisation is:

The SEI Process Maturity Model or The Capability Maturity Model(CMM)

Level 1: InitialLevel 2: RepeatableLevel 3: DefinedLevel 4: ManagedLevel 5: Optimizing

At each level, Key Process Areas (KPAs) provide goals

The SEI ProcessMaturity Model ...

Level 1: Initial– process is ad hoc and sometimes

chaotic– few processes defined – success depends upon individual effort

Key Process Areas (KPAs)»none

The SEI Process Maturity Model ...

Level 2: Repeatable– basic project management processes defined– process discipline in place to repeat successes

Key Process Areas»software configuration management»software quality assurance»software subcontract management»software project tracking»software project planning» requirements management


Level 3: Defined– process is documented, standardised and

integrated into a standard software process– all projects use this standard software process

Key Process Areas»peer reviews» intergroup coordination»software product engineering» integrated software management» training program»software process definition and focus


Level 4: Managed– detailed measures of software process and

product quality are collected– process and products are quantitatively

controlled

Key Process Areas»quality management»qualitative process management


Level 5: Optimizing– continuous process improvement is enabled– there is quantitative feedback from the

process and from piloting innovative ideas and technologies

Key Process Areas»process change management»technology change management»defect prevention


or Capability Maturity Model (CMM)– is the best available description of the

goals, methods and practices needed for the industrial practice of software engineering

But how do we do this in the classroom?– this is the role of the PSP

i.e. the Personal Software Process

The Personal Software Process or PSP

• PSP Objectives:– To introduce students to a process-based

approach to developing software– To show students how to measure, estimate,

schedule, and track their work– To show students how to improve the quality

of their programs

– In general PSP improves quality and productivity

• The time saved in testing because of better quality reduces time across the project by 20-40%

The Personal Software Process or PSP

a self improvement process designed to

help you be a better software engineer help you control, manage and improve the

way you work requires research and study of your

work needs personal motivation to pay off

The Personal Software Process

PSP helps you to:» manage your work & assess/build your

talents/skills» plan better» track your performance precisely» measure the quality of your software products

- as a framework for determining:» why you make errors and how you find them» the quality of your reviews» the types of errors you make


PSP has a maturity framework like CMM- some KPAs are removed eg training program

Structure:PSP0: establish a measured performance baselinePSP1: make size, resource and schedule plansPSP2: learn defect and yield managementPSP3: scale up PSP methods to larger projects


Baseline Process - PSP0– includes some basic measurements and a

reporting format– the process you currently use to write software

but enhanced to provide measurements

PSP0.1 - PSP0 enhanced by adding: »a coding standard»size measurement and size counting

standard»process improvement proposal (PIP)


The Personal Planning Process (PSP1)– adds planning steps to PSP0

»test report»size and resource estimation

PSP1.1– establishes a performance rate for planning– PSP1 enhanced by adding

»task planning»schedule planning


The Personal Quality Management Process (PSP2)– adds review techniques to PSP1 to help

you find defects early»design reviews»code reviews

PSP2.1– establishes design completeness criteria

»design templates


A Cyclic Personal Process (PSP3)– for large programs e.g. 10,000 LOC

– subdivide into PSP2-sized modules– enhance the base module in iterative cycles– in each iteration do a complete PSP2

including design, code, compile, test– effective scale up from base module to large

program if each increment is of a high quality


• The parts of PSP you will be using: •PSP0 for Stage 1 of your assignment•PSP1 & 2 for Stages 2 & 3 of your

assignment

•The following documents:Time Log, Defect Log and Project Summary - use manually (refer Attachments) or - use electronically in PASEWEB

(Personal Assistant for Software Engineers)

•Process scripts and instructions(refer Attachments)


• The PSP uses 3 types of measures:– Effort, Size and Defects

• Effort measurement• Measured in minutes• Students keep records of time spent on tasks• Interruption time is recorded and subtracted

• Size measurement• Size will be measured in number of lines of code and FP

• Defect measurement• Students record changes to correct an error• Fix time and defect type is recorded


PSP Logic - based on the Principles:• Need measured historical data for effective

planning• A defined process can improve working efficiency• Defined personal processes should fit the individual

skills of the software engineer• Continuous process improvement is enhanced by

rapid and explicit feedback

Competent work is possible when professionals know the basic methods of their field and practice them with discipline.

Summary

The CMM sets out the principal practices for managing the processes in large-scale software development

The PSP sets out the principal practices for defining, measuring and analysing an individual’s own processes

Appendix – Application Domains

Data-Centred Systems Many business applications - payroll,

inventory control Often centred on a database, with

user interaction objects, and ability to generate customised reports.

Essentially passive - you do things to the data periodically.

Application Domains ...

Real-time Systems Air-line reservations, air-traffic control,

nuclear power station Reactive. Things are happening all the

time to change the state of the system. Parallelism, inter-process

communication States and events Direct real-world interfacing Concern with messages, signals,

control parameters.


Systems Programs Concerned with the control of computer

resources - memory, disk, ports, buses. Software is Operating systems, device

drivers, IOCS, compilers etc. Shares many of the concerns of real-

time systems. In addition has terms like interrupts,

masks, registers etc. which relate specifically to computer resource allocation and control


Life/mission-critical systems Heart monitor, air-traffic control,

rocket launch, nuclear power plant... Typically real-time, often embedded Extra-high reliability requirement

– e.g. Department of Defense specifies the quality standards, and languages to be used in development of its systems.


Scientific/Engineering Concerned with scientific and engineering

calculations Evaluation of complex formulae Sophisticated numerical or statistical

methods. Low on input and output

Spatial Information Systems (GIS) Mass data storage Map coordinate digitization, scanning and

image processing, relational DB, SQL


Knowledge-based Systems Knowledge acquisition, building a

knowledge base, expert system shell, inference mechanisms.

Networks/Data Communications Including distributed components and

intranet, internet, WAN, LAN Other

Office automation, EDI, CAD/CAM

the software engineering process and the personal software process (psp)

Documents

methodsthe software

wrong software process

software projectswork

building software

workthe software

quality software products

team of software engineers

processesthe software