Verification and Validation: A Quick Introduction

AuthorsMassood Towhidnejad

Mike Rowe David Dampier

Sponsored In Part by NSF Grant EEC-0080502 And published on www.swenet.org

Learning Objectives1. The student will be able to define both verification and

validation, and to know the difference between them.2. The student will be able to identify the appropriate activities

and their classification as either verification or validation.3. The student will be able to distinguish between verification

and validation, given a set of activities.4. Given a set of software artifacts, the student will understand

the appropriate verification or validation activity to that artifact.

5. Given a set of projects in different categories, the student will be able to determine which category of projects would require more V&V activity, and which would require less.

6. Given a set of defects and the phases of development in which they were found, the student will be able to estimate the relative cost of correcting errors early or late in the lifecycle.

Why Invest in Quality? Cost effective Provides competitive edge Essential for business survival Essential for international marketing Helps to retain customers, and

increase profits Hallmark of world class business

Ways to Improve Quality Prevention of Defects

• Process Improvement• Complexity Reduction• Risk Management• Causal Analysis

Detection and Correction of Defects• Verification• Validation• Rework• Causal Analysis

Verification

Verification – Are we building the product right?

Verification is any checking process conducted on software artifacts in an attempt to determine if they work as specified by the designers of the system.

Includes reviews, inspections, walkthroughs, unit testing and integration testing.

Validation

Validation – Are we building the right product?

Validation is the process of evaluating software artifacts during the software development process in an attempt to determine if the system works as required by the customers. Any evaluation activity that involves the customer can be used for validation purposes.

Includes program reviews, system testing, customer acceptance testing.

Verification vs. Validation Verification

• Main purpose is to detect defects in the artifacts of the system under development.

Validation• Main purpose is to show that the system

under development meets user needs, requirements, and expectations.

Verification & Validation Techniques

Static Methods• Techniques applied to artifacts without

execution. Dynamic Methods

• Techniques applied to artifacts through execution.

Mathematically Based Methods

Static: Reviews Walkthroughs

• Code verification• Document

ConOps, SRS validation STEP, SAD, SDD verification

Inspections• Code verification• Document Audits verification

Program Reviews• Customer involved validation• No customer verification

Effectiveness of Static VerificationEffectiveness of Static Verification

More than 60% of program defects can be detected by program inspections.

More than 90% of program defects may be detectable using more rigorous mathematical program verification.

The defect detection process is not confused by the existence of previous defects.

Dynamic: Testing (Verification)

Unit Test (Detailed Design): • Testing the individual software modules,

components, or units. Integration Testing (Architectural Design):

• After unit test, the system is put together in increments. Integration testing focuses on the interfaces between software components (OO thread-based, cluster-based testing)

System Testing (Requirements Spec): • One goal of system testing is to ensure that

the system functions as specified in the specification.

Dynamic: Testing (Validation)

System Testing (Requirements Spec):• Another goal of system testing is to ensure

that the system functions as the client expected in a controlled environment.

User Acceptance Test (ConOps):• A set of formal tests run for the client, and

specified by the client. When the system passes these tests, the software has been accepted by the client as meeting the requirements.

Verification and Validation in the Development Lifecycle

CodeExecute Unit

Tests

White-Box &Black-Box

Testing

Black-BoxTesting

RequirementsAnalysis

ExecuteSystem Tests

Execute Integration

TestsDesign

Validate the System

Verify Design

Verify Implementation

Review

s

Mathematics-Based Verification

Verification is based on mathematical arguments which demonstrate that a program is consistent with its specification.

Programming language semantics must be formally defined.

The program must be formally specified.

Why Inspection is important? Relative cost to fix a defect Phase in which found Cost ratio

(hours)– Requirement 1– Design 3-6– Coding 10– Testing 15-70– Operation 40-1000

Data derived from Capers Jones.

Costs of Finding and Fixing Late

Delays in identifying and fixingdefects gets geometrically more

expensive as the lifecycle progresses!

$1

$10

$100

$1000

Cost

of

Fix

ing

a D

efe

ct

Defe

cts

Time in (Phase of) Development

Cost of Quality Includes all costs of quality-related

activities. Quality costs =

+Prevention costs+Detection and Appraisal costs+Failure costs

• Internal failure costs• External failure costs

Cost of Quality (COQ) – refers to the cost of correcting defects once found.

Quality Cost Components Direct Cost

– Reviews/inspections– Unit testing– System testing– Acceptance testing– Test planning and

design– Computer time– Resources (terminals,

staffs, etc.)

Indirect Cost– Rework– Recovery– Corrective action cost– Failures– Analysis meeting– Debugging– Retesting– Legal fees

Verification or… Validation?

Reviews

Unit Testing Integration Testing System Testing Acceptance Testing

Verification or… Validation?

Reviews Either

Unit Testing

Integration Testing System Testing Acceptance Testing

Verification or… Validation?

Reviews Either

Unit Testing Verification

Integration Testing

System Testing Acceptance Testing

Verification or… Validation?

Reviews Either

Unit Testing Verification

Integration Testing Verification

System Testing

Acceptance Testing

Verification or… Validation?

Reviews Either

Unit Testing Verification

Integration Testing Verification

System Testing Validation

Acceptance Testing

Verification or… Validation?

Reviews Either

Unit Testing Verification

Integration Testing Verification

System Testing Validation

Acceptance Testing Validation

Balancing Trade-Offs What is the real requirement? What are the expected benefits of

V & V vs.– cost of increasing V&V activity– additional time required– technical feasibility– risk of not finding defects

» delivery» operation

“When is it good enough?”(Bach, 1997)

Summary Verification and Validation are both

important to the quality of software. Each is different:

• Verification determines that what we are doing is done correctly.

• Validation determines whether we are doing the right thing.

Sometimes, less quality is okay. Some software systems require less V&V, as the cost is not supportable. Some require more no matter what it costs.

The earlier defects are discovered, the less it will cost to correct them.

Backup Slides

• Design • Coding

• System Requirements• Contractor Management

• Evaluate Requirements• Evaluate Design

• Monitor Tests• Integration

TestedProducts

Discrepancies

Subs

Project Manager

IV&V

• Testing

Independent Verification and Validation (IV&V)

Static and Dynamic Verification & Validation

Formalspecification

High-leveldesign

Requirementsspecification

Detaileddesign Program

Prototype Dynamicvalidation

Staticverification

Sommerville, p. 421

Test Case Development in the V Model

Code Execute Unit

Tests

Test cases designed and executed by developers

Test cases designedand executed by

independent testers

RequirementsAnalysis

ExecuteSystem Tests

Execute Integration

TestsDesign

Validate Requirements

Verify Design

Verify Implementation