1 CS 4312 Software Engineering Requirements Luiz Marcio Cysneiros Fall 2006.

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CS 4312 Software Engineering

Requirements

Luiz Marcio Cysneiros

Fall 2006

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Textbook

Requirements engineering : processes and techniques

Gerald Kotonya and Ian Sommerville.

Publication info: Chichester ; New York : J. Wiley & Sons, c1998. ISBN: 0471972088

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Classes Tuesday/Thursday Time 4:00 PM – 5:30 PMRoom CSB 129

Mid-term Exam TBAFinal Exam TBA

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Scoring

Assignments 10 points each (2)

Mid-term exam 35 points

Final exam 45 points

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Assignments Policy

Due dates To be specified• Since Assignments are in groups of no less

than 3 and no more than 4, late assignments won’t be accepted

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Final and Round up

• Final = Everything goes on it

• No Round up

• Ex: 49.8 = E

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Directions

email [email protected]

office TEL Building 3051

Office Hours – Tuesday and Wednesdays and 11:00 A.M. - Noon

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The Course at a Glance

• Introduction

• Elicitation

• Modelling

• Analysis

• Management

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Requirement: (Macmillan English Dictionary)1. something that is needed in order for

something to happen:– Check the car’s fuel requirements.

– Good insulation can cut the energy requirements of a house by more than half.

2. something that a rule, law, contract, etc. states that you must do:

– Do these goods comply with our safety requirements?

– requirement of: It is usually a requirement of banks and investors that a new company is formed to effect the management buy-out.

– requirement for: Applicants must satisfy the requirements for admission to the university.

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System: a set of interrelated components, or sub-systems, with a particular purpose. 1) there are 2 components at least, 2) each of which is related (directly or indirectly) to every other component and, 3) no sub set of which is unrelated to any other subset. Ackoff, Russell L., (1971). Towards a System of Systems Concepts. Management science, 17(11), 661-71.

1. [count] a set of connected things that work together for a particular purpose:

– a central heating system

I decided to install a security system to prevent any break-ins.

– the capital’s inadequate public transportation system

System: (Macmillan English Dictionary)

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Context

• Software crises continues– Denver Airport

• More than 50 million US $ due to errors in the

baggage control system

– London Ambulance Service• The system was deactivated one day after its

deployment due to many errors. Most of them related to non-functional requirements such as: Safety, Reliability and Usability

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Software Crises

• Flaws in the Production Process

Unhappy Clients High costs

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Europe

• Questionnaire sent to 3.805 companies showed:

• For the Analysts Major problems are:– Requirements specification (53%)– Requirements Management (43%)– Documentation (36%)– Test (35%)

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USA• Requirements Management (Also know as

Requirements Engineering – RE) is seen as one of the most important problems to be overcome in order for companies to achieve level 2 in the SEI’s (Software Engineering Institute – Carnegie Mellon) CMM (Capability Maturity Model)

• SEI has recently released a package aiming to transfer technology in RE to facilitate companies’ certification

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“26% of the Software projects were considered a success.”

Standish Group, CHAOS Report, 2000

Good News …

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Meaning that 74% have FAILED!

Standish Group, CHAOS Report, 2000

Bad News…

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Tom De Marco

“56% of the errors in a software can be traced back to the requirements phase”

• The later an error is detected the more expensive is to fix it.

• Many errors are done during Requirements elicitation and analysis

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Schach’s Summary

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• Many errors in requirements can (and should) be detected early in the software development life cycle.

• Typical errors include: Use of incorrect facts, omission, inconsistency and ambiguity.

• Errors in requirements specification are one of the major concerns for software industry.

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Cost to Repair

Analysis Design Code Unit Test Integration Test

Maintenance

Stage when the Error is found

200 x

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Definition

“ Requirements engineering is a sub-area of Software Engineering that studies the process of defining the requirements for a software-to-be. It is a new area started in 1993 when the 1st International Symposium on RE was organized. This Year we had the 13th edition of this congress.

The process for defining requirements is an interface between the desires and the needs of the clients and a future implementation of these requirements as a software.”

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Another Definition

• RE is:

“The development and use of technology effective to elicit, specify and analyse requirements from stakeholders (clients/users) that shall be performed by a software system.”

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Goals

• Understand the needs and support the client’s desires.

• Provide the Software Engineer with methods, techniques and tools to help on the process of understanding and registering what a software must do.

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Fred Brook’s

• Brook adds:

“The most difficult part of building a software system is to decide, precisely, what must be built. No other part of the work can undermine so badly the resulting software if not done correctly. No other part is so difficult to fix later.”

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• Requriements Engineering as a discipline: 1993– RE (93, 95, 97, 99. 01)

– ICRE (94, 96, 98, 00)

– WER (98, 99, 00, 01)

– Requirements Engineering Journal

• Past : System Analysis

• Today : A network of processes– Pressure from the market for quality(CMM e ISO)

– Books (Sommerville, Jackson, Loucopoulos, …)

– Tools (Doors, Requisite-Pro, Caliber-RM)

Brief History

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Books

• Requirements Engineering: Processes and Techniques by Ian Sommerville, Gerald Kotonya (September 1998) John Wiley & Son Ltd; ISBN: 0471972088 Amazon.com Sales Rank:

188,502 • System Requirements Engineering by Pericles Loucopoulos, Vassilios

Karakostas (June 1995) McGraw Hill Text; ISBN: 0077078438 Amazon.com Sales Rank: 1,067,908

• Software Requirements & Specifications : A Lexicon of Practice, Principles and Prejudices by Michael Jackson (July 1995) Addison-Wesley Pub Co; ISBN: 0201877120 Amazon.com Sales Rank:

38,607

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More Books

• Exploring Requirements : Quality Before Designby Donald C. Gause and Gerald M. Weinberg (September 1989) Dorset House; ISBN: 0932633137 Amazon.com Sales Rank: 13,641

• Mastering the Requirements Process by Suzanne Robertson, James Robertson (May 4, 2000) Addison-Wesley Pub Co; ISBN: 0201360462 ; Dimensions (in inches): 0.93 x 9.50 x 7.66 Amazon.com Sales Rank: 7,392

• Managing Software Requirements: A Unified Approach (The Addison-Wesley Object Technology Series)by Dean Leffingwell, Don Widrig (November 1999),Addison-Wesley Pub Co; ISBN: 0201615932 Dimensions (in Inches): 1.13 x 9.46 x 7.76 Amazon.com Sales Rank: 14,447

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Links for Information on RE

• http://www.telelogic.com/products/doorsers• http://www.starbase.com/• http://www.rational.com/products/reqpro/

index.jtmpl• http://www.cs.ucl.ac.uk/research/renoir/• http://www.shu.ac.uk/tfre/• http://www.re01.org http://www.re05.org• http://link.springer.de/link/service/journals/

00766/index.htm

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Factors influencing requirements

• Personality and status of stakeholders

• The personal goals of individuals within an organisation

• The degree of political influence of stakeholders within an organisation

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Process improvement

• Process improvement is concerned with modifying processes in order to meet some improvement objectives

• Improvement objectives– Quality improvement– Schedule reduction– Resource reduction

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Planning process improvement

• What are the problems with current processes?

• What are the improvement goals?

• How can process improvement be introduced to achieve these goals?

• How should process improvements be controlled and managed?

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RE process problems• Lack of stakeholder involvement• Business needs not considered• Lack of requirements management• Lack of defined responsibilities• Stakeholder communication problems• Over-long schedules and poor quality requirements

documents• Many confuse it with Design• Pressure from the Market

– “It has to be ready next week”• Clients keep adding and changing things

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Process maturity

• Process maturity can be thought of as the extent that an organization has defined its processes, actively controls these processes and provides systematic human and computer-based support for them.

• The SEI’s Capability Maturity Model is a framework for assessing software process maturity in development organizations

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Capability maturity model

Level 3Defined

Level 2Repeatable

Level 1Initial

Level 4Managed

Level 5Optimizing

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RE process maturity model

Level 1 - InitialAd-hoc requirements

engineering; requirementsproblems are common

Level 2 - RepeatableStandardised requirements

engineering; fewerrequirements problems

Level 3 - DefinedDefined process basedon best practice; processimprovement in place

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RE process maturity levels• Initial level

– No defined RE process. Suffer from requirements problems such as requirements volatility, unsatisfied stakeholders and high rework costs. Dependent on individual skills and experience.

• Repeatable level– Defined standards for requirements documents and policies and

procedures for requirements management.

• Defined level– Defined RE process based on good practices and techniques.

Active process improvement process in place.

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Maturity levels• Managed level

– Detailed measurements of both process and product quality are collected and used to control the process.

• Optimizing level – The organisation has a continuous process

improvement strategy, based on objective measurements in place.

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Good practice for RE process improvement

• RE processes can be improved by the systematic introduction of good requirements engineering practice

• Each improvement cycle identifies good practice guidelines and works to introduce them in an organisation

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MANAGEMENT

PEOPLE

METHODS

TOOLS

INFORMATION

Keep the state of the art

Establish goals

Produce software

Support creative work

supportmethods

Manage the SDS

Build a team

Measure the process

Create systems

organizesystems

processinformation

Implement policies

Guarantee policies are followed

record software

reuseinformation

givefeedback

Software Development System

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Most Common Scenario

• Structured Analisys

• Structured Project

• Essential Analysis

• Entity-Relationship Model

• Objects

• CASE

• Automatic Genaration of Applications

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Abstraction X Formalism

Ideal

Conventional

Abstract

Concrete

Con

cret

e/A

bst

ract

Informal Linguistic Level Formal

Talk Specification Code

Very High Level

High LevelLow Level

MachineLevel

Goal

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Why Requirements Engineering?

Von Neumann:

“There is no sense in being precise when you don’t even know what you are talking about”

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Problems• Management Support

• Availability of Processes

• Integration of Platforms

• Education vs Ignorance

• Cost

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The Context of RE

• Information System

• Engineering Systems

• Organizations Producing Software

• Models

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Clients

Needs

Users

Limitations

Impossibilities

Technological Infra-Structure

So, What are Requirements?

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Types of Requirements

• Customized Systems– Built inside the organization (in house)– Built by third parties

• General Products – Production and selection

• Specific Products– Production and selection

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Definitions• Software Requirements

– Sentences that express clients’ needs and establish the desired quality

• Functional Requirements – FR are the requirements that are directly related to the

software functionality.– What the system must do !

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Definitions

• Non-Functional Requirements– NFRs express constraints that a software must comply

with.

– Can be seen as specific qualities that a software must have

– “How” the software must do the “What”

• Requirements-1 (Inverse Requirements)– IR establish conditions that must never happen

– Frequently associated to an NFR

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After all, What are Requirements?FR

NFR

IR

NFR

Clients

Needs

Users

Limitations

Impossibilities

Technological Infra-Structure

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Definitions• Requirement

– Necessary condition to achieve a certain goal, or the fulfillment of a certain goal

• Specification– Detailed description of the characteristic that a

material, work, or service must present

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Examples• The system should provide a form to enter results for

clinical tests performed for a client (RF)

• Depending on the result of the test, only the Supervisor can entry the result for this patient. E.g Glucose over 8.0 (NFR Safety)

• The system should give the client a receipt. This should take no longer than 8 sec (FR “.” NFR Performance)

• The system can not erase any client information (IN)

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Ecologic Aspects

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Definitions

• Universe of Discourse– Is the context in which the software should be developed and

operated. UofD includes all the sources of information and all the people related to the software. These people are also known as the actors of this universe. UofD is a reality circumstantiated by the set of goals defined by those who demand the software

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Information Systems

Universe of Information

MacrosystemSoftwareSystem

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organization

software

hardwareInformation System

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Where We Are

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DefinitionsRequirements Engineering establish the process of requirements definition as a process during which what has to be done has to be elicited modelled and analyzed. This process must deal with different viewpoints and use a combination of methods, tools and personnel. The product of this process is a model from which a document called requirements is produced. This process is continual and happens in a context previously defined to which we call Universe of Discourse

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An SADT Model for the Definition of Requirements

SelectSelectPersonelPersonel

SelectSelectPersonelPersonel

Soft. Eng. Viewpoints

clientsmethod

ElicitElicitElicitElicit

ModelModelModelModel

facts

requirements

model

tools

AnalyseAnalyseAnalyseAnalyseSelect Select MethodMethodSelect Select MethodMethod

UofD

UofD

UofD

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Reading for next Class

• Requirements Engineering - a roadmap - Nuseibeh, Easterbrook

• [Goguen94] - Goguen, J.A. and Linde, C. - Techiques for Requirements Elicitation, In   Proceedings of the First IEEE International Symposium on Requirements Engineering, San Diego, Ca, IEEE Computer Society Press - 1994,  pp 152-164. 

• [Goguen94a] - Goguen, Joseph - Requirements Engineering as the reconciliation of social and technical issues - in Requirements Engineering: Social and Technical Issues edited by Joseph Goguen and Marina Jirotka - Academic Press 1994.

• Download from course page