What are the Requirements?

October 8, 2019

Each developer works with requirements constantly. Below we will share detailed information on what is a requirement, how to create excellent requirements, requirements level, and benefits from good requirements. This material is not for BA, it is a short introduction for developers and delivery, a short BaBok quiz.

The article is a summary and quotes from the book.

Requirement definition

Requirement is formulated necessity

The BABOK defines a standard requirement as a condition or capability needed by a stakeholder to solve a problem or achieve an objective.

Levels of Requirements

At each step of your work, you need to understand the reasons for some requirements occurrences. If you understand business requirements it is much easier to create optimal solution requirements.

Levels of Requirements — The image from the book

Business requirements are the highest level of requirements and are developed during Enterprise Analysis activities. They define the high-level goals, objectives, and needs of the organization. Business requirements are progressively elaborated into the next level of detail, the stakeholder requirements.

Stakeholder requirements define the needs of stakeholders and how they will interact with a solution. Stakeholder requirements bridge between the high-level business requirements and the more detailed solution requirements.

Solution requirements describe the solution characteristics that will be needed to meet the higher-level business and stakeholder requirements. Solution requirements are subdivided into three types: functional, non-functional, and transition requirements.

Functional requirements define the capabilities that a product must provide to its users while non-functional requirements describe quality attributes, design and implementation constraints, and external interfaces that the product must have.

Transition requirements define the solution capabilities required to transition from the current to the future state and are no longer needed once the transition is complete.

Non-functional requirements

Requirements are often missed during communication. It is great to have some check-list before the communication session starts

Characteristics of Excellent Requirements

Good requirements should be:

Unambiguous
Testable (verifiable)
Clear (concise, terse, simple, precise)
Correct
Understandable
Feasible (realistic, possible)
Independent
Atomic
Necessary
Implementation-free (abstract)

Unambiguous

REQ1 The system shall not accept passwords longer than 15 characters.

It is not clear what the system is supposed to do:

The system shall not let the user enter more than 15 characters.
The system shall truncate the entered string to 15 characters.
The system shall display an error message if the user enters more than 15 characters.

The corrected requirement reflects the clarification:

REQ1 The system shall not accept passwords longer than 15 characters. If the user enters more than 15 characters while choosing the password, an error message shall ask the user to correct it.

Testable (Verifiable)

Some words can make a requirement untestable:

Some adjectives: robust, safe, accurate, effective, efficient, expandable, flexible, maintainable, reliable, user-friendly, adequate

Some adverbs and adverbial phrases: quickly, safely, in a timely manner

Nonspecific words or acronyms: etc., and/or, TBD

Clear

REQ1 Sometimes the user will enter Airport Code, which the system will understand, but sometimes the closest city may replace it, so the user does not need to know what the airport code is, and it will still be understood by the system.

This sentence may be replaced by a simpler one:

REQ1 The system shall identify the airport based on either an Airport Code or a City Name.

Correct

If a requirement contains facts, these facts should be true:

REQ1 Car rental prices shall show all applicable taxes (including 6% state tax).

The tax depends on the state, so the provided 6% figure is incorrect.

Independent

To understand the requirement, there should not be a need to know any other requirement:

REQ1 The list of available flights shall include flight numbers, departure time, and arrival time for every leg of a flight.

REQ2 It should be sorted by price.

The word “It” in the second sentence refers to the previous requirement. However, if the order of the requirements changes, this requirement will not be understandable.

Feasible (Realistic, Possible)

REQ1 The system shall have a natural language interface that will understand commands given in the English language.

This requirement may be not feasible within a short span of development time.

Atomic

The requirement should contain a single traceable element:

REQ1 The system shall provide the opportunity to book the flight, purchase a ticket, reserve a hotel room, reserve a car, and provide information about attractions.

This requirement combines five atomic requirements, which makes traceability very difficult. Sentences including the words “and” or “but” should be reviewed to see if they can be broken into atomic requirements.