Cs 641 requirements engineering
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CS 641 – Requirements Engineering. Chapters 6-7. Agenda. Fit Criterion Functional Requirements Non-functional Requirements. Fit Criteria Definition.

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CS 641 – Requirements Engineering

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CS 641 – Requirements Engineering

Chapters 6-7


  • Fit Criterion

  • Functional Requirements

  • Non-functional Requirements

Fit Criteria Definition

  • “If there is a requirement for the product to carry out some function, then the testing activity must demonstrate that the product indeed performs that function or have that property.”

  • Therefore, the requirement must have a benchmark or fit criterion to compare against.

  • The fit criterion is some quantification of the product that demonstrates the standard the product must attain.

Scale of Measurement

  • The unit that is used to test conformance

  • Examples:

    • Speed of operation – microseconds, minutes

    • Usability – time needed to learn product, time taken to achieve an agreed level of competence, error rate of work done

    • Component Color - % of various colors

    • Sound – loudness/softness measured in decibels

    • Light – measured in lumens

    • Typefaces – measured by type names and point sizes

Chapter 6 – Functional Requirements

  • Specifications of the products functionality

  • Actions the product must take:

    • Check

    • Calculate

    • Record

    • Retrieve

  • Derived from the fundamental purpose of the product

  • Not a quality

How to Find Them

  • Example: the business context is broken into business events.

  • Business events determine the product’s use cases.

  • For each use case we build a scenario

  • Each of the steps in the scenario is a task that the actor describes.

  • The tasks or steps are described in the actor’s language, so it may be general or at a high-level to describe the details of the product’s capabilities.

  • These steps provide a vehicle for determining all of the functional requirements that are needed by each step.

Use Case Steps for Discovering Functional Requirements


Use Case



















Functional Requirements – Level of Detail

  • These are business requirements that can be verified by business people.

  • If you use a Use case – this should be enough to describe what the product does to complete the work.

  • Later designers can add technical requirements.

  • Note at this level the way the requirements are defined – they are not yet testable or measurable.

  • Fit criterion will be applied to each requirement so that it can be measured and tested.

  • Watch out for ambiguity.

Fit Criteria for Functional Requirements

  • For functional requirements, there are no scales of measurement

  • The action is either completed or not

  • Completion will depend on satisfying an authority

    Either the source of the data or the adjacent system that initiated the action

  • The resulting action has resulted in correct manipulation of the data

Functional Requirement Fit Criteria: Example

Description: The product shall record the weather station


Fit criterion: The recorded weather station readings shall

match the readings sent by the weather station.

Chapter 7 – Non-functional Requirements

Non-functional Requirements

  • They do not alter the products essential functionality

  • Discovered during trawling & prototyping

  • Usually describes the “experience” a user has while performing work

  • Are properties that the functionality must have

  • It can represent the use case as a whole or one of the specific functional requirements

Use Case Non-functional Requirement Representation

Look & Feel


Use Case













Types of Non-functional Requirements

  • Look and Feel Requirements – the spirit of the product’s appearance

  • Usability Requirements – the product’s ease of use, and special usability considerations

  • Performance Requirements – how fast, how safe, how many, how accurate the functionality must be

  • Operational Requirements – the operating environment of the product, and what considerations must be made for that environment

  • Maintainability and Portability Requirements – expected changes, and the time allowed to make them happen

  • Security Requirements – the security and confidentiality of the product

  • Cultural and Political Requirements – special requirements that come about because of the people involved in the product’s development and operation

  • Legal Requirements – what laws and standards apply to the product

Non-functional Fit Criteria

  • A fit criterion for non-functional requirements quantifies a particular quality that a product must have.

  • These qualities include such things as: usability, look & feel, performance, security, etc.

Look & Feel Requirements - Type 10

  • Should Cover:

    • Highly readable

    • Apparently simple to use

    • Approachable, so that people do not hesitate to use

    • Authoritative, so that users rely on it and trust it

    • Conforming to the client’s other products

    • Colorful and attractive

    • Unobtrusive so that people are not aware of it

    • Innovative and appearing to be state of art

    • Professional or executive looking

    • Exciting

    • Interactive

Look & Feel Requirements –Sample wording

  • Description: The product shall provide a graphic and colorful view of all the roads in the district.

  • The product shall be conservative.

  • The product shall appear authoritative.

  • The product shall be colorful.

  • The product shall be attractive to a teenage audience.

  • The product shall appear artistic.

  • The product shall be stat of the art.

  • The product shall have an expensive appearance.

  • The product shall conform to established look & fell of the organization’s requirements.

Non-functional Requirement Fit Criteria: Look & Feel Requirements Example

Fit criterion: The product shall conform to “company colors”.

Fit criterion: The product shall conform to interface

guidelines as established in ….

Fit criterion: The product shall have a comprehension level

of an eight grader..

Non-functional Requirement Fit Criteria: User-Friendly Example

Description: The product shall be user friendly.

Fit criterion: New users shall be able to add, change and

delete roads within 30 minutes of their first attempt at

using the product.

Fit criterion: Within three months of introducing the product,

60% of the users shall be using it to carry out the agreed

work. From those users, the product shall receive a 75%

or more approval rating.

Usability Requirements - Type 11

  • Should Cover:

    • Rate of acceptance by the users

    • Productivity gained as a result of the product’s introduction

    • Error rates (or reduction thereof)

    • Being used by people who do not speak native language

    • Accessibility to handicapped people

    • Being used by people with no previous experience with computers

Usability Requirements –Sample wording

  • The product shall be easy to use.

  • The product shall be easy to use by members of the public who may have only one free hand.

  • The product shall be easy to use by graduate engineers.

  • The product shall be easy to learn.

  • Description: The product shall be able to be used by a member of the public without training.

  • Fit Criterion: 90% of a panel representative of the general public shall successfully purchase a ticket form the product on their first encounter.

Non-functional Requirement Fit Criteria: Usability Requirements Example

Description: The product shall be intuitive and self-explanatory.

Fit criterion: A road engineer shall be able to produce a

correct de-icing forecast within ten minutes of encountering

the product for the first time.

Fit criterion: Nine out of ten road engineers shall be able to successfully complete [list of selected tasks] after one day’s


Non-functional Requirement Fit Criteria: Subjective Tests Example

Fit criterion: The product shall not be offensive to 85% of

a test panel representing the makeup of the people likely

to come in contact with the product. No more than 10% of

the interest groups represented in the panel shall feel


Performance Requirements - Type 12

  • Aspects include:

    • Speed to complete a task

    • Accuracy of the results

    • Safety to the operator

    • Volumes to be held by the product

    • Ranges of allowable values

    • Throughput such as the rate of transactions

    • Efficiency of resource usage

    • Reliability – usually expressed as mean time between failures

    • Availability – up time or time periods that users may access the product

    • Expandability of most of the above

Non-functional Requirement Fit Criteria: Performance Requirements Example

Description: The response shall be fast enough to avoid interrupting the user’s flow of thought.

Fit criterion: The response time shall be no more than 1.5

seconds for 95% of the responses, and no more than 4

seconds for the remainder.

Fit criterion: In the first three months of operation, the product shall be available for 98% of the time between 8am and 8pm.

Non-functional Requirement Fit Criteria: Product Failure Example

Description: The product must produce the road de-icing

schedule in an acceptable time.

Fit criterion: The road de-icing schedule shall be available

to the engineer within 15 seconds for 90% of the times

that it is produced. The remaining times it will be available

within 20 seconds.

Operational Requirements - Type 13

  • Can Cover:

    • Operating environment

    • Condition of the users

    • Partner or collaborating systems

    • Portable products

Non-functional Requirement Fit Criteria: Operational Requirements Example

Description: The product shall be used in and around trucks, operating at freezing temperatures, at night. It is most likely raining or snowing. Salt and water are expected to come into contact with the product. Lighting will be poor. The operator will be wearing gloves.

Fit criterion: the operator shall successfully complete [list of tasks] within [time allowed] in a simulation of a 25-year storm (this is an accepted quantification of meteorological conditions) and the product shall function correctly after 24 hours exposure.

Fit criterion: the interfaces to the DM31 Weather Station shall comply with the specifications issued by Saltworks Systems.

Maintainability Requirements - Type 14

  • Should Cover Anticipated changes to:

    • Organization

    • Environment

    • Laws that apply to the product

    • Business rules

Non-functional Requirement Fit Criteria: Maintainability Requirements Example

Fit criterion: New users shall be added to the system with no more than five minutes disruption to existing users.

Security Requirements - Type 15

  • Should Cover:

    • Confidentiality

    • Integrity

    • Availability

Non-functional Requirement Fit Criteria: Security Requirements Example

Description: Only engineers using category A logons shall be able to alter the weather station data.

Fit criterion: Of 1000 alterations of the weather station data, none shall be from logons other than category A engineer logons.

Cultural & Political - Type 16

  • Should Cover:

    • Acceptable solutions

    • Unacceptable solutions

    • Differentiating from existing products or work styles

    • Politics

    • Religious observances

    • Political correctness

    • Spelling

Non-functional Requirement Fit Criteria: Cultural & Political Requirements Example

Fit criterion: The Shatnez Laboratory in Brooklyn shall certify that the product compiles with the Shatnez rules.

Fit criterion: Stan Hood of the auditing department shall approve the interface before it goes into production.

Fit criterion: The marketing department shall certify that all components are American made.

Legal Requirements - Type 17

  • Facilitate compliance:

    • Examine adjacent systems or actors that have contact with your product.

    • Consider legal requirements & rights.

    • Are there laws that are relevant to this product (privacy, data protection, guarantees, consumer credit, consumer protection, right to information, etc…)

Non-functional Requirement Fit Criteria: Legal Requirements Example

Fit criterion: The legal department/company lawyers shall certify that the product complies with the [applicable laws.

Non-functional Requirement Fit Criteria: Solution Constraints Example

Description: The software part of the product must run with the Linux system.

Fit criterion: The software part of the product shall comply with the specification of S.U.S.E. Linux release 5.2.

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