Advanced Software Engineering Lecture 2: The Software Process.

Advanced Software Engineering

Lecture 2: The Software Process

Today’s Topics The role of process in SE Typical process elements Evolution of processes (CMM) Specific life-cycle models Associated Reading:

Chapter 4 in SEPA 5/e

Fundamental Questions

What is the problem to be solved? What are the characteristics of a possible

solution? How will the solution be designed? How will the solution be built? How will we test the design and implementation? How will we maintain over time?

3 Conceptual Phases Definition

• What is to be constructed?

Development• How shall we construct it?

Support• How will we maintain it over time?

Who are the Players? Roles

• Client: person(s) requesting the SW

• Developer: person(s) building the SW

• User: person(s) using the SW

User and client may be different! Internal SW development vs.

contract SW development

Typical Activities (Phases)

Requirements Elicitation (Phase) Specification Phase Design Phase Implementation Phase Integration Phase Maintenance Phase Retirement Phase

Requirements Elicitation (Phase)

What’s the problem? What are the constraints?

• Cost, deadlines, performance, platform, …

Elicitation of requirements Successive refinement

• Technical feasibility

• Financial justification

Requirements [2] Challenges:

• “I know this is what I asked for, but it’s not what I needed”

• Software is complex

• The customer doesn’t understand the problem well

Possible Solution: rapid prototyping

Specification Phase Specification Document

• Explicit description of functionality

• Explicit list of constraints

• List of inputs and outputs

Specification is a Contract• Includes acceptance criteria

• Should be written as precisely as possible!

Specification Phase [2]

Challenges• Ambiguous: a specification has more than one interpretation

• Incomplete: an important specification is omitted

• Contradictory: two statements about the same situation which don’t agree

Possible Solution:formal specification review

Design Phase

Specification=“what” to build Design=“how” to build it Data flow Modular decomposition Algorithms and data structures Two components:

• Architectural Design (global level)• Detailed Design (module level)

Design Phase [2]

Challenges:• Generality vs. Complexity

• Planning for future enhancements

• Design for reusability, maintainability

Approach:• Be explicit about your goals

• Conduct formal design reviews

Implementation Phase

Coding up the data structures, algorithms, and modules Commenting the code Separate written documentation Testing document, test cases Unit (module) Testing Evaluation:

formal code walk-throughs

Integration Phase

Combine all the modules Realistic operational tests Methods

• Bottom-up integration

• Top-down integration

Challenges• Both methods have drawbacks

• Best to integrate while implementing

Integration Phase [2]

Product Testing• Developer vs. SQA group

• Installation testing

• Documentation testing

• Performance testing

• Robustness testing

Acceptance Testing• Client tests specified functionality

Maintenance Phase Activities

• Correction

• Adaptation

• Enhancement

• Prevention

Integration• Regression testing

Retirement Phase

Good software is maintained Sometimes software is rewritten from scratch

• Software is now unmaintainable because• A drastic change in design has occurred• The product must be implemented on a totally new

hardware/operating system• Documentation is missing or inaccurate• Hardware is to be changed—it may be cheaper to rewrite the software

from scratch than to modify it

True retirement is a rare event

Process-Specific Difficulties

Does the product meets the user’s real needs? Is the specification document free of ambiguities,

contradictions, and omissions?

Umbrella Activities

Project tracking, formal reviews Formal technical reviews Quality assurance Configuration management Documentation preparation and production Reusability management Measurement / testing Risk management

Common process framework Tasks Milestones, deliverables SQA points

Process Evolution How can we measure the effectiveness of our SE

processes? Reflective practice involves a cycle of

measurement, analysis, and adjustment(“learning from experience”)

Capability Maturity Model (CMM)

Improving the Software Process

U.S. Department of Defense initiative Software Engineering Institute (SEI) The fundamental problem with software

• The software process is badly managed

Improving the Software Process (contd)

Software process improvement initiatives• Capability maturity model (CMM)

• ISO 9000-series

• ISO/IEC 15504

Capability Maturity Model

Not a life-cycle model A set of strategies for improving the software process

• SW–CMM for software• P–CMM for human resources (“people”)• SE–CMM for systems engineering• IPD–CMM for integrated product development• SA–for software acquisition

These strategies are being unified into CMMI (capability maturity model integration)

SW–CMM

A strategy for improving the software process Put forward in 1986 by the SEI Fundamental ideas:

• Improving the software process leads to• Improved software quality• Delivery on time, within budget

• Improved management leads to• Improved techniques

Five levels of “maturity” are defined Organization advances stepwise from level to level

Level 1. Initial Level

Ad hoc approach• Entire process is unpredictable

• Management consists of responses to crises

Most organizations world-wide are at level 1

Level 2. Repeatable Level

Basic software management• Management decisions should be made on the basis of

previous experience with similar products• Measurements (“metrics”) are made• These can be used for making cost and duration predictions in

the next project• Problems are identified, immediate corrective action is taken

Level 3. Defined Level

The software process is fully documented• Managerial and technical aspects are clearly defined

• Continual efforts are made to improve quality, productivity

• Reviews are performed to improve software quality

• CASE tools are applicable now (and not at levels 1 or 2)

Level 4. Managed Level

Quality and productivity goals are set for each project• Quality, productivity are continually monitored

• Statistical quality controls are in place

Level 5. Optimizing Level

Continuous process improvement• Statistical quality and process controls

• Feedback of knowledge from each project to the next

Summary

Key Process Areas

There are key process areas (KPAs) for each level Level 2 KPAs include:

• Requirements management• Project planning• Project tracking• Configuration management• Quality assurance

Compare• Level 2: Detection and correction of faults• Level 5: Prevention of faults

Experience

It takes:• 3 to 5 years to get from level 1 to level 2

• 1.5 to 3 years from level 2 to level 3

• SEI questionnaires highlight shortcomings, suggest ways to improve the process

Original idea:• Defense contracts would be awarded only to capable

firms

Experience (contd)

Profitability• Hughes Aircraft (Fullerton, CA) spent $500K (1987–90)

• Savings: $2M per year, moving from level 2 to level 3

• Raytheon moved from level 1 in 1988 to level 3 in 1993• Productivity doubled

• Return of $7.70 per dollar invested in process improvement

Other SPI Initiatives Other software process improvement (SPI) initiatives:

• ISO 9000-series

• ISO/IEC 15504

ISO 9000

Set of five standards for industrial activities• ISO 9001 for quality systems

• ISO 9000-3, guidelines to apply ISO 9001 to software

• There is an overlap with CMM, but they are not identical

• Not process improvement

• Stress on documenting the process

• Emphasis on measurement and metrics

• ISO 9000 is required to do business with the E.U.

• Also by many U.S. businesses, for example, GE

• More and more U.S. businesses are ISO 9000 certified

ISO/IEC 15504

Original name: Software Process Improvement Capability dEtermination (SPICE)• International process improvement initiative

• Started by British Ministry of Defence (MOD)

• Includes process improvement, software procurement

• Extends and improves CMM, ISO 9000

• Framework, not a method• CMM, ISO 9000 conform to this framework

• Now referred to as ISO/IEC 15504

• Or just 15504 for short

Process Improvement Data

SEI report on 13 organizations in the original study They used a variety of process improvement techniques, not

just SW–CMM

Process Improvement Data (contd)

Results of 34 Motorola projects

Software Process Models

Strategies encompassing process, methods, tools and generic steps

Choice based on nature of the application Cycle: from status quo, to new problem

definition, to new technical development, to solution integration (Figure 2.3a, SEPA 5/e)

The Basic Process Loop

[from SEPA 5/e]

Steps:• System engineering

• Requirements analysis

• Design

• Code generation

• Testing

• Maintenance

Linear Sequential Model

Linear Sequential Model

[From SEPA 5/e]

Linear Sequential Model

Challenges:• Real projects rarely follow sequential flow (changes cause

confusion)

• Difficult for customer to state requirements explicitly

• Customer must have patience

• Developers sometimes delayed unnecessarily (‘blocking states’)

Prototyping Model

Steps: • Listen to customer

• Build prototype

• Customer “test drives” prototype

Challenges:• “Throw-away” phenomenon

• Demos can set unrealistic expectations

• Compromises that solidify

Prototyping Model

[From SEPA 5/e]

RAD Model

Rapid Application Development Linear sequential, short cycle

(60-90 days) Steps:

• Business modeling• Data modeling• Process modeling• Application generation• Testing and turnover

Rapid ApplicationDevelopment (RAD)

[From SEPA 5/e]

RAD Model

Challenges:• For large projects, sufficient resources are needed for rapid

cycle

• Strong commitment from developers and customers

• Presupposes modular solution

• Reusability sometimes implies loss of performance

The Incremental Model

Linear sequential, with iterative prototyping “Core product” vs. incremental enhancements Each increment operational Useful when human/machine resources are

limited

Incremental Model[From SEPA 5/e]

The Spiral Model

Iterative prototyping, with framework activities For example:

• First circuit: specification

• Second circuit: prototype

• Third circuit: product release

Includes development and maintenance

Spiral Model

[From SEPA 5/e]

The Spiral Model (2)

Challenges:• Hard to show controllability

(size and timing of each circuit)

• Risk assessment is fundamental

• Model fairly new (less experience)

WINWIN Spiral

A variation of the standard Spiral Model Identify key “stakeholders” Determine stakeholder win conditions Reconcile win conditions into a set of win-win

conditions for the whole project

WINWIN Spiral

[From SEPA 5/e]

Component Assembly Model

Spiral Model, plus object-oriented reusability Challenges:

• Reusability requires careful planning

• Most existing programs are not reusable

• More suitable for particular application domains(with significant patterns of reuse)

Component Assembly[From SEPA 5/e]

Concurrent Development

State charts for each activity Events trigger state transitions Useful for interorganizational development Useful where there is a high degree of

interdependence between different modules (e.g., client-server apps)

Concurrent DevelopmentModel

[From SEPA 5/e]

Other Models

Formal Methods• Rigorous mathematical (logical) specification of software

• Formal models are time-consuming

• Requires developer, customer skill

Fourth Generation Techniques• High-level definition language

• E.g., UML -> Java code generation

• Benefits small/midsize projects most

Product and Process

Advances in one area trigger advances in another “Pendulum” phenomenon “The process should be as enjoyable as the

product”

Questions?