James Nowotarski 3 October 2006 SE 325/425 Principles and Practices of Software Engineering Autumn...

James Nowotarski

3 October 2006

SE 325/425Principles and

Practices of Software Engineering

Autumn 2006

2

Topic Duration

Finish risk management 30 minutes

Requirements process 45 minutes

*** Break

Current event reports 30 minutes

Requirements process 60 minutes

Wrap-up 15 minutes

Today’s Agenda

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“The basic problem of software development is risk”

Beck, K. (2000). Extreme Programming Explained. Boston, MA: Addison-Wesley

Risk management

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Categories of software risk

Project Technical Business Legal

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“It is futile to try to eliminate risk”

-- Peter Drucker, management guru

Risk management

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Risk management process

Identify Analyze Plan

Cost of protection Cost of exposure

$$ $$

Control

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Risk management process: artifacts

Identify Analyze Plan Control

• List of risks • Probability• Impact• Cutoff• Risk exposure

• Mitigation plan• Monitoring plan• Contingency plan

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“Worrying about what might go wrong may not be as glamorous a job as speculating about the future, but it is a more essential job right now.”

Carr, N. (2003, May). IT doesn’t matter. Harvard Business Review. Retrieved September 8, 2006 from EBSCO Host – Business Source Premier database.

Does SE Matter?

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Topic Duration

Finish risk management 30 minutes

Requirements process 45 minutes

*** Break

Current event reports 30 minutes

Requirements process 60 minutes

Wrap-up 15 minutes

Today’s Agenda

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Quote

“The hardest single part of building software is deciding what to build” – Fred Brooks

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Survey Results[plus Jordan] [plus all DL]

Key issues/trends: Outsourcing 11 Security 7 Web 2.0 6 Requirements 1/5 Dispersed teams 5 Speed of delivery 4 Project mgmt 3/1 Six sigma/Quality 4/1 Agile methods 4 Upgrades 3 IT working with business units 2 Commoditization of IT/SW 2 Others 1

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Areas of most disruptive change

Software requirements Program design

- Winston W. Royce

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Context

Communication project initiation requirements

Modeling analysis design

Construction code test

Deployment delivery support

Planning & Managing

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Context

Communication project initiation requirements

Modeling analysis design

Construction code test

Deployment delivery support

Planning & Managing

elicitation Requirementsengineeringtasks (Ch. 7-8)

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Context

Communication project initiation requirements

Modeling analysis design

Construction code test

Deployment delivery support

Planning & Managing

elicitationRequirementsengineeringtasks (Ch. 7-8)

elaborationspecification

Chapter 7

Chapter 8

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Context

Communication project initiation requirements

Modeling analysis design

Construction code test

Deployment delivery support

Planning & Managing

elicitationRequirementsengineeringtasks (Ch. 7-8)

elaborationspecification

Primarydeliverables

functional reqtsnon-functional reqts

analysis modelsoftware reqts spec

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What is a requirement?

A requirement can be defined simply as a property of a system, or a constraint upon the product or process by which the system is to be created

IEEE Std 610.12-1990 defines a requirement as

A condition or capability needed by a user to solve a problem or achieve an objective.

A condition or capability that must be met or possessed by a system or system component to satisfy a contract, standard, specification, or other formally imposed documents.

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Functional vs. Non-Functional

A functional requirement (FR) describes what the system needs to do.

Example: ‘The system shall display the current customer balance’.

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Functional vs. Non-Functional

A non-functional requirement (NFR) describes a constraint upon the solution space.

Examples: Performance, flexibility, reliability, usability, portability, maintainability, safety, and security.Also called “quality” requirements, “ilities”, or even “systemic” requirements. Emergent Properties: An NFR that is realized through the careful implementation of other requirements on which it depends. Example: “The query must return its results in less than three seconds” is only realizable once the architecture and much of the system functionality has been implemented.

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Quote

“It’s not enough to do good. It must be done well” – St. Vincent de Paul

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Management involvement and governance

Senior management needs to be involved in critical business/IT decisions

Educating management is a technique to help users who “don’t know what they want”

High degree of involvement helps to improve the strategic business value of information technology

Example: What security and privacy risks will we accept?

Senior management needs to lead the decision making

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The Requirements Process

Elicitation: Proactively working with stakeholders to discover their needs, identify potential conflicts, and establish a clear scope and boundaries for the project.

Elaboration (Analysis): Gaining a deeper understanding of the product and its interactions.

Specification: Production of a series of documents that capture the system and software requirements in order to support their systematic review, evaluation, and approval.

Validation: Inspecting requirements to ensure their correctness.

Management: Issues such as software configuration management, traceability, impact analysis, and version control.

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Key Question: Deliverables

Steps Techniques

What does the system need to do?How well does it need to do it?

Functional requirementsQuality requirements

1. Review as-is system2. Identify requirements of

to-be system

Re-engineering AHPInterviewing PrototypingObservationSurveys/Focus GroupsJoint Application Design (JAD)Benchmarking

Elicitation

Roles Estimating guidelines

Business analyst

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Elicitation Techniques

Collaborative sessions are useful for brainstorming and problem solving activities.

A Joint Application Design (JAD) can bring together a small group of stakeholders to form initial goals and requirements.

Helps to avoid ambiguity

Helps to reduce scope creep

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Joint Application Design (JAD)

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Elicitation Techniques

Interviewing techniques are simple yet effective.

Structured around a specific set of questions

Closed ended

Open ended

Can be conducted in stages, so that responses from the first round can be used to generate a deeper set of more focused questions for the second round.

Can be expensive

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Elicitation Techniques

Observation involves observing the way users interact with an existing system.

Useful when users are unable to fully articulate their needs, or are too busy to attend other types of elicitation meetings. Observe how tasks are executed, problems, shortcuts, & areas for improvement. Sometimes referred to as “going to the gemba”Especially good for uncovering unstated requirements

“Exciting requirements” – Exceed user’s initial expectations

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Elicitation Techniques

Prototyping – taking an early set of requirements and using them to elicit further requirements.

Low fidelity models useful because for very little cost you can obtain useful feedback from the user. Higher fidelity prototypes enable the user to interact with something closer to the finished product.

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Elicitation Techniques

Analytic Hierarchy Process (AHP) – a mathematically-based prioritization technique

Represents the elements of any problem hierarchicallyGuides decision makers through a series of pairwise comparisonsResults in quantitative assessment of relative strength of requirements Developed by Dr. Thomas Saaty of the University of Pittsburgh

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Elicitation Techniques: AHP

Develop QualitySoftware Goal

ArchitectureChoice 1

ArchitectureChoice 2 Alternatives

Performance Usability FlexibilityQualityreqts

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Elicitation Techniques: AHP

Develop Software

Performance Usability Flexibility

ArchitectureChoice 1

ArchitectureChoice 2

Goal

Alternatives

Qualityreqts

.08 .64 .28

.41.59

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Activity: AHP

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Context ModelsDetermine the boundaries of the system.

What is the system?What is the system’s environment?

Develop a context model that shows the context of the system within its environment.

Auto-TellerSystem

SecuritySystem

MaintenanceSystem

Branchaccounting

System

BranchcounterSystem

AccountDatabase

UsageDatabase

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Context Models

Understand the types of interaction the software system has with its adjacent systems.

Some adjacent systems cooperate with your system through two-way communication. Consider them black-box components of your system.

Some adjacent systems initiate events and interact with your system (i.e., people).

Some adjacent systems have one way communication but otherwise work autonomously.

Trigger events that must be specified.

Incoming communication may trigger an event to be specified. Also don’t forget TIMED events

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Model these interactions as Use Cases

Identify actors

Model their interactions with the system.

Through elicitation fully explore all the ways each actor may interact with the system.

Banking Software Product

Withdraw Money

Customer Teller

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Requirement Qualities

Each individual requirement should be:

Concise

Correct

Non-ambiguous

Feasible

Verifiable

Traceable

Manageable

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Concise

A requirement should describe a single property of the desired system and should include no information beyond that necessary to describe the intended property.

It should be stated in clear, simple, and understandable terms.

Note the need to define terms such as “Emergency calls” and “Public” in the requirements definition document.

Emergency calls from the public shall be answered in the order in which they are received.

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Correct

A requirement should accurately describe the intended property of the intended system.

No information missing that is needed to define or implement the system.

The following requirement is obviously (or at least probably should be) incorrect:

When an ambulance crew is dispatched to pick-up a patient more than 2 miles away, they shall wait three minutes before departing in order to give the dispatch operator the chance to locate a closer crew.

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Non-ambiguous A requirement should be stated clearly and

understandably, in order to avoid ambiguous interpretations.

The following requirement is OBVIOUSLY ambiguous. Why?

How could you fix it?

When a call is received the dispatcher assigns the job to the best crew.

Shoes mustbe worn!

Dogs mustbe carried!

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What is wrong with this requirement?

“The same display shall also be able to generate a visible or audible caution/warning sign for the attention of the ambulance driver or medic.”

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Conjunctions are dangerous…

Disambiguate what the ‘and’ means…

The battery low warning lamp shall light up when the voltage drops below 3.6 Volts, and the current workspace or input data shall be saved.

We can separate the requirement into multiple parts…

The battery low warning lamp shall light up when the voltage drops below 3.6 Volts.

When the battery low warning lamp lights up the current workspace shall be saved.

The battery low warning lamp shall remain lit until the voltage rises above 3.7 Volts.

?? Go back to the stakeholder

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Conjunctions are dangerous…

Problems arise when readers try to puzzle out which part applies.

The battery low warning lamp shall light up when the voltage drops below 3.6 Volts, and the current workspace shall be saved.

Or disambiguate…

The battery low warning lamp shall light up when the voltage drops below 3.6 Volts, and then the current workspace shall be saved.

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Conjunctions are dangerous…

What about this requirement?

An aircraft that is non-friendly and has an unknown mission or the potential to enter restricted airspace within 5 minutes shall raise an alert.

Again – disambiguate and/or precedence. Two options:

An aircraft that is non-friendly and (has an unknown mission or the potential to enter restricted airspace within 5 minutes) shall raise an alert.

If [an aircraft is non-friendly] and [has an unknown mission or the potential to enter restricted airspace within 5 minutes], the system shall <raise> <an alert>.

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Feasible

A requirement should be feasible from a technical, financial, and managerial perspective.

The following requirement is INFEASIBLE except possibly in a James Bond movie!

This is just overly optimistic wishful thinking because we didn’t specify anything about traffic congestion, location of the patient, distance to the hospital etc.

All patients shall be delivered to a hospital within 5 minutes of their pick-up.

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Verifiable

A requirement should be written in such a way as to provide a clear and testable acceptance criterion.

For example, it is not sufficient to specify that:

Instead, the requirement should be written in a verifiable form such as:

The dispatcher must be able to quickly identify the closest open emergency room.

The dispatcher must be able to identify the closest open emergency room within 1 second.

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Traceable

A requirement is traceable if it has been assigned a unique ID and if it is focused on one property.

For example a requirement stating that:

creates traceability problems because it involves tracking the implementation of crew allocations and ambulance allocations.

A driver and medic shall be assigned to an ambulance crew and the crew shall be assigned to an ambulance.

Never build in let-out or escape clauses(if, when, but, except, unless, although)

The forward passenger doors shall open automatically when the aircraft has halted, except when the rear ramp is deployed.

The fire alarm shall always be sounded when smoke is detected, unless the alarm is being tested or the engineer has suppressed the alarm.

Don’t ramble

Provided that the designated input signals from the specified devices are received in the correct order where the system is able to differentiate the designators, the output signal shall comply with the required framework of section 3.1.5 to indicate the desired input state.

Refrain from designing the system

The antenna shall be capable of receiving FM signals, using a copper core with nylon covering and a waterproof hardened rubber shield.

Avoid mixing different kinds of requirements Do not speculate

Users normally require early indication of intrusion into the system.

Do not play on ambiguous requirementsAlways make requirements as clear as possible

Do not use vague undefinable termsThe print dialog shall be versatile and user-friendly

Do not express possibilitiesThe reception subsystem probably ought to be powerful enough to receive a signal inside a steel-framed building.

Avoid wishful thinkingThe gearbox shall be 100% safe in normal operationThe network shall handle all unexpected errors without crashing.

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Manageable

Attributes should be used to support requirements management.

For example:

Date created

Date last edited

Priority (High, Mid, Low etc)

Status (Completed, Undergoing Change, Scheduled, Unassigned).

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Qualities of a Good Set of Requirements

Realistic: The requirements should represent realistic goals at both the product and project level.

Concise: The requirements as a whole should concisely describe the system that is to be developed. Long-winded requirements create greater opportunity for ambiguity and errors.

Complete: The requirements should collectively describe the entire system to be implemented with no information missing.

Consistent: Inconsistencies between requirements lead to conflicts that prohibit all of the requirements being implemented successfully. Inconsistencies should be identified and conflicts negotiated.

Begin with the end in mind - Sample SRSOverviewRevision HistoryTable of Contents1.0 Introduction

1.1 Purpose1.2 Scope1.3 References1.4 Assumptions and Dependencies

2.0 Use-Cases3.0 Requirements

3.1 Functional Requirements3.2 Non-Functional Requirements

3.2.1 Usability3.2.2 Reliability3.2.3 Performance3.2.4 Supportability

4.0 Online User Documentation and Help System

Requirements5.0 Design Constraints6.0 Purchased Components7.0 Interfaces

7.1 User Interfaces7.2 Hardware

Interfaces7.3 Software Interfaces7.4 Communication

Interfaces8.0 Licensing Requirements9.0 Legal, Copyright, and Other

notices10.0 Applicable StandardsIndexGlossary

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Topic Duration

Finish risk management 30 minutes

Requirements process 45 minutes

*** Break

Current event reports 30 minutes

Requirements process 60 minutes

Wrap-up 15 minutes

Today’s Agenda

53

Read Pressman Chapters 13-14 (Testing) Current Event Reports:

FitzgeraldMaroseMikaelNan

For October 10

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Extra slides

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Testing

Requirements

Functional Design

TechnicalDesign

DetailedDesign

Code

Unit Test

IntegrationTest

SystemTest

AcceptanceTest

Flow of Work

Verification

Validation

Testing: Test that the product implements the specification

Legend:

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Change Control Process

Create InitialSections

Create/ModifyDraft

Review Draft(V&V)

Create Changes to Incorporate

Changes Needed In Document

DocumentApproved

Create Review Revise ReviewReview Approved

Time

...

Document in Production and Under Formal Change Control

Document in Production and Under Formal Change Control

Document Under Development and User Change Control

Document Under Development and User Change Control

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Waterfall model

Systemrequirements

Softwarerequirements

Analysis

Program design

Coding

Testing

Operations

Source: Royce, W.  "Managing the Development of Large Software Systems."

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RUP Artifacts by Phase and Discipline

Discipline Inception Elaboration Construction TransitionBusiness Modeling

RequirementsVisionUse Cases (20-80%)ActorsSoftware Req SpecGlossary

Analysis & Design Software Arch Doc

Implementation

Build PlanBuildTest Results

Test

Test PlanTest ScriptTest DataTest Results

Test Strategy

DeploymentDeployment Plan Training Materials

Support MaterialsAcceptance Test ResultsChange Requests

Product

Executable ArchitectureUser Interface PrototypeUser Interface DesignUse Case RealizationDesign ModelDatabase Design

Business Architecture

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RUP Artifacts by Phase and Discipline

Discipline Inception Elaboration Construction Transition

Configuration and Change Management

Project Management Risk ListRisk Mgmt PlanBusiness CaseQA PlanSoftware Dev Plan

Environment

Dev Case (Process)ToolsGuidelinesTemplatesSupport

CM PlanCM EnvironmentChange Requests

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Risk vs. Technology Maturity

Impact of Technology Maturity

Risk Early Adopter Mid Adopter Late Adopter

hands-on implementation experience little exper / high riskmore exper / mid risk

much exper / low risk

vendor survival for project after shake-out high risk mid risk low risk

sudden changes in direction of technology high risk mid risk low riskintegrating technology with existing portfolio

high risk mid risk low risk

Benefits

Period for Start of Payoff  Short term Mid term Long term

Size of Returns per period Biggest Bigger  Big 

Risk vs. Return

Flow of Extension ActivitiesFlow of Extension Activities

Describe Use Case

Perform Use Case Analysis

Model User Experience

Identify Design Elements

Implement Elements

Design Classes

Design Subsystems & Components

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Technology

ProcessPeople

The focus of SE 425 is the process component of software engineering

Core Concepts

Technology

ProcessPeople

… for the delivery of technology-enabled business solutions