Specifying requirements

This is a printer-friendly version. It omits exercises, optional topics (i.e., four-star topics), and other extra content such as learning outcomes.

Prose

What

A textual description (i.e. prose) can be used to describe requirements. Prose is especially useful when describing abstract ideas such as the vision of a product.

The product vision of the TEAMMATES Project given below is described using prose.

TEAMMATES aims to become the biggest student project in the world (biggest here refers to 'many contributors, many users, large code base, evolving over a long period'). Furthermore, it aims to serve as a training tool for Software Engineering students who want to learn SE skills in the context of a non-trivial real software product.

Avoid using lengthy prose to describe requirements; they can be hard to follow.

Feature lists

What

Feature list: A list of features of a product grouped according to some criteria such as aspect, priority, order of delivery, etc.

A sample feature list from a simple Minesweeper game (only a brief description has been provided to save space):

  1. Basic play – Single player play.
  2. Difficulty levels
    • Medium-levels
    • Advanced levels
  3. Versus play – Two players can play against each other.
  4. Timer – Additional fixed time restriction on the player.
  5. ...

User stories

Introduction

User story: User stories are short, simple descriptions of a feature told from the perspective of the person who desires the new capability, usually a user or customer of the system. [Mike Cohn]

A common format for writing user stories is:

User story format: As a {user type/role} I can {function} so that {benefit}

Examples (from a Learning Management System):

  1. As a student, I can download files uploaded by lecturers, so that I can get my own copy of the files
  2. As a lecturer, I can create discussion forums, so that students can discuss things online
  3. As a tutor, I can print attendance sheets, so that I can take attendance during the class

You can write user stories on index cards or sticky notes, and arrange on walls or tables, to facilitate planning and discussion. Alternatively, you can use a software (e.g., GitHub Project Boards, Trello, Google Docs, ...) to manage user stories digitally.

[credit: https://www.flickr.com/photos/jakuza/2682466984/]

[credit: https://www.flickr.com/photos/jakuza/with/2726048607/]

[credit: https://commons.wikimedia.org/wiki/File:User_Story_Map_in_Action.png]

Details

The {benefit} can be omitted if it is obvious.

As a user, I can login to the system so that I can access my data

It is recommended to confirm there is a concrete benefit even if you omit it from the user story. If not, you could end up adding features that have no real benefit.

You can add more characteristics to the {user role} to provide more context to the user story.

  • As a forgetful user, I can view a password hint, so that I can recall my password.
  • As an expert user, I can tweak the underlying formatting tags of the document, so that I can format the document exactly as I need.

You can write user stories at various levels. High-level user stories, called epics (or themes) cover bigger functionality. You can then break down these epics to multiple user stories of normal size.

[Epic] As a lecturer, I can monitor student participation levels

  • As a lecturer, I can view the forum post count of each student
    so that I can identify the activity level of students in the forum
  • As a lecturer, I can view webcast view records of each student
    so that I can identify the students who did not view webcasts
  • As a lecturer, I can view file download statistics of each student
    so that I can identify the students who do not download lecture materials

You can add conditions of satisfaction to a user story to specify things that need to be true for the user story implementation to be accepted as ‘done’.

As a lecturer, I can view the forum post count of each student so that I can identify the activity level of students in the forum.

Conditions:

Separate post count for each forum should be shown
Total post count of a student should be shown
The list should be sortable by student name and post count

Other useful info that can be added to a user story includes (but not limited to)

  • Priority: how important the user story is
  • Size: the estimated effort to implement the user story
  • Urgency: how soon the feature is needed
More examples extra

User stories for a travel website (credit: Mike Cohen)

  • As a registered user, I am required to log in so that I can access the system
  • As a forgetful user, I can request a password reminder so that I can log in if I forget mine
  • [Epic] As a user, I can cancel a reservation
    • As a premium site member, I can cancel a reservation up to the last minute
    • As a non-premium member, I can cancel up to 24 hours in advance
    • As a member, I am emailed a confirmation of any cancelled reservation
  • [Epic] As a frequent flyer, I want to book a trip
    • As a frequent flyer, I want to book a trip using miles
    • As a frequent flyer, I want to rebook a trip I take often
    • As a frequent flyer, I want to request an upgrade
    • As a frequent flyer, I want to see if my upgrade cleared

Usage

User stories capture user requirements in a way that is convenient for i.e. which features to include in the productscoping, i.e. how much effort each feature will takeestimation, and i.e. when to deliver each featurescheduling.

[User stories] strongly shift the focus from writing about features to discussing them. In fact, these discussions are more important than whatever text is written. [Mike Cohn, MountainGoat Software 🔗]

User stories differ from e.g. a description of the requirements written in prosetraditional requirements specifications mainly in the level of detail. User stories should only provide enough details to make a reasonably low risk estimate of how long the user story will take to implement. When the time comes to implement the user story, the developers will meet with the customer face-to-face to work out a more detailed description of the requirements. [more...]

User stories can capture non-functional requirements too because even NFRs must benefit some stakeholder.

Requirements → Requirements →

Non-functional requirements

Requirements can be divided into two in the following way:

  1. Functional requirements specify what the system should do.
  2. Non-functional requirements specify the constraints under which system is developed and operated.

Some examples of non-functional requirement categories:

  • Data requirements e.g. size, how often do data changevolatility, saving data permanenetlypersistency etc.,
  • Environment requirements e.g. technical environment in which system would operate or need to be compatible with.
  • Accessibility, Capacity, Compliance with regulations, Documentation, Disaster recovery, Efficiency, Extensibility, Fault tolerance, Interoperability, Maintainability, Privacy, Portability, Quality, Reliability, Response time, Robustness, Scalability, Security, Stability, Testability, and more ...
  • Business/domain rules: e.g. the size of the minefield cannot be smaller than five.
  • Constraints: e.g. the system should be backward compatible with data produced by earlier versions of the system; system testers are available only during the last month of the project; the total project cost should not exceed $1.5 million.
  • Technical requirements: e.g. the system should work on both 32-bit and 64-bit environments.
  • Performance requirements: e.g. the system should respond within two seconds.
  • Quality requirements: e.g. the system should be usable by a novice who has never carried out an online purchase.
  • Process requirements: e.g. the project is expected to adhere to a schedule that delivers a feature set every one month.
  • Notes about project scope: e.g. the product is not required to handle the printing of reports.
  • Any other noteworthy points: e.g. the game should not use images deemed offensive to those injured in real mine clearing activities.

You may have to spend an extra effort in digging NFRs out as early as possible because,

  1. NFRs are easier to miss e.g., stakeholders tend to think of functional requirements first
  2. sometimes NFRs are critical to the success of the software. E.g. A web application that is too slow or that has low security is unlikely to succeed even if it has all the right functionality.

Given below are some requirements of TEAMMATES (an online peer evaluation system for education). Which one of these are non-functional requirements?

  • a. The response to any use action should become visible within 5 seconds.
  • b. The application admin should be able to view a log of user activities.
  • c. The source code should be open source.
  • d. A course should be able to have up to 2000 students.
  • e. As a student user, I can view details of my team members so that I can know who they are.
  • f. The user interface should be intuitive enough for users who are not IT-savvy.
  • g. The product is offered as a free online service.

(a)(c)(d)(f)(g)

Explanation: (b) are (e) are functions available for a specific user types. Therefore, they are functional requirements. (a), (c), (d), (f) and (g) are either constraints on functionality or constraints on how the project is done, both of which are considered non-functional requirements.

An example of a NFR captured as a user story:

As a I want to so that
impatient user to be able experience reasonable response time from the website while up to 1000 concurrent users are using it I can use the app even when the traffic is at the maximum expected level

Given their lightweight nature, user stories are quite handy for recording requirements during early stages of requirements gathering.

Here are some tips for using user stories for early stages of requirement gathering:

  • Define the target user:
    Decide your target user's profile (e.g. a student, office worker, programmer, sales person) and work patterns (e.g. Does he work in groups or alone? Does he share his computer with others?). A clear understanding of the target user will help when deciding the importance of a user story. You can even give this user a name. e.g. Target user Jean is a university student studying in a non-IT field. She interacts with a lot of people due to her involvement in university clubs/societies. ...
  • Define the problem scope: Decide that exact problem you are going to solve for the target user. e.g. Help Jean keep track of all her school contacts
  • Don't be too hasty to discard 'unusual' user stories:
    Those might make your product unique and stand out from the rest, at least for the target users.
  • Don't go into too much details:
    For example, consider this user story: As a user, I want to see a list of tasks that needs my attention most at the present time, so that I pay attention to them first.
    When discussing this user story, don't worry about what tasks should be considered needs my attention most at the present time. Those details can be worked out later.
  • Don't be biased by preconceived product ideas:
    When you are at the stage of identifying user needs, clear your mind of ideas you have about what your end product will look like.
  • Don't discuss implementation details or whether you are actually going to implement it:
    When gathering requirements, your decision is whether the user's need is important enough for you to want to fulfil it. Implementation details can be discussed later. If a user story turns out to be too difficult to implement later, you can always omit it from the implementation plan.

While use cases can be recorded on e.g. index cards or sticky notesphysical paper in the initial stages, an online tool is more suitable for longer-term management of user stories, especially if the team is not physically in the same locationco-located.

You can create issues for each of the user stories and use a GitHub Project Board to sort them into categories.

Example Project Board:

Example Issue to represent a user story:

A video on GitHub Project Boards:

Example Google Sheet for recording user stories:

Example Trello Board for recording user stories:

eXtreme Programming (XP)eXtreme Programming (XP)

Extreme programming (XP) is a software development methodology which is intended to improve software quality and responsiveness to changing customer requirements. As a type of agile software development, it advocates frequent "releases" in short development cycles, which is intended to improve productivity and introduce checkpoints at which new customer requirements can be adopted. [wikipedia, 2017.05.01]

uses User stories to capture requirements.

This page in their website explains the difference between user stories and traditional requirements.

One of the biggest misunderstandings with user stories is how they differ from traditional requirements specifications. The biggest difference is in the level of detail. User stories should only provide enough detail to make a reasonably low risk estimate of how long the story will take to implement. When the time comes to implement the story developers will go to the customer and receive a detailed description of the requirements face to face.

Use cases

Introduction

Use case: A description of a set of sequences of actions, including variants, that a system performs to yield an observable result of value to an actor.[ 📖 : uml-user-guideThe Unified Modeling Language User Guide, 2e, G Booch, J Rumbaugh, and I Jacobson ]

Actor: An actor (in a use case) is a role played by a user. An actor can be a human or another system. Actors are not part of the system; they reside outside the system.

A use case describes an interaction between the user and the system for a specific functionality of the system.

System: Online Banking System (OBS)
Use case: UC23 - Transfer Money
Actor: User
MSS:
  1. User chooses to transfer money.
  2. OBS requests for details of the transfer.
  3. User enters the requested details.
  4. OBS requests for confirmation.
  5. User confirms.
  6. OBS transfers the money and displays the new account balance.
  Use case ends.
Extensions:
  3a. OBS detects an error in the entered data.
    3a1. OBS requests for the correct data.
    3a2. User enters new data
    Steps 3a1-3a2 are repeated until the data entered are correct.
    Use case resumes from step 4.
  
  3b. User requests to effect the transfer in a future date.
      3b1. OBS requests for confirmation.
      3b2. User confirms future transfer.
      Use case ends.
  
  *a. At any time, User chooses to cancel the transfer.
      *a1. OBS requests to confirm the cancellation.
      *a2. User confirms the cancellation.
      Use case ends.
  • System: A Learning Management System (LMS)
  • Actor: Student
  • Use Case: Upload file
    1. Student requests to upload file
    2. LMS requests for the file location
    3. Student specifies the file location
    4. LMS uploads the file

UML includes a diagram type called use case diagrams that can illustrate use cases of a system visually, providing a visual ‘table of contents’ of the use cases of a system.

In the example on the right, note how use cases are shown as ovals and user roles relevant to each use case are shown as stick figures connected to the corresponding ovals.

Unified Modeling Language (UML) is a graphical notation to describe various aspects of a software system. UML is the brainchild of three software modeling specialists James Rumbaugh, Grady Booch and Ivar Jacobson (also known as the Three Amigos). Each of them has developed their own notation for modeling software systems before joining force to create a unified modeling language (hence, the term ‘Unified’ in UML). UML is currently the de facto modeling notation used in the software industry.

Use cases capture the functional requirements of a system.

Glossary

What

Glossary: A glossary serves to ensure that all stakeholders have a common understanding of the noteworthy terms, abbreviations, acronyms etc.

Here is a partial glossary from a variant of the Snakes and Ladders game:

  • Conditional square: A square that specifies a specific face value which a player has to throw before his/her piece can leave the square.
  • Normal square: a normal square does not have any conditions, snakes, or ladders in it.

Supplementary requirements

What

A supplementary requirements section can be used to capture requirements that do not fit elsewhere. Typically, this is where most Non Functional Requirements will be listed.

Requirements → Requirements →

Non-functional requirements

Requirements can be divided into two in the following way:

  1. Functional requirements specify what the system should do.
  2. Non-functional requirements specify the constraints under which system is developed and operated.

Some examples of non-functional requirement categories:

  • Data requirements e.g. size, how often do data changevolatility, saving data permanenetlypersistency etc.,
  • Environment requirements e.g. technical environment in which system would operate or need to be compatible with.
  • Accessibility, Capacity, Compliance with regulations, Documentation, Disaster recovery, Efficiency, Extensibility, Fault tolerance, Interoperability, Maintainability, Privacy, Portability, Quality, Reliability, Response time, Robustness, Scalability, Security, Stability, Testability, and more ...
  • Business/domain rules: e.g. the size of the minefield cannot be smaller than five.
  • Constraints: e.g. the system should be backward compatible with data produced by earlier versions of the system; system testers are available only during the last month of the project; the total project cost should not exceed $1.5 million.
  • Technical requirements: e.g. the system should work on both 32-bit and 64-bit environments.
  • Performance requirements: e.g. the system should respond within two seconds.
  • Quality requirements: e.g. the system should be usable by a novice who has never carried out an online purchase.
  • Process requirements: e.g. the project is expected to adhere to a schedule that delivers a feature set every one month.
  • Notes about project scope: e.g. the product is not required to handle the printing of reports.
  • Any other noteworthy points: e.g. the game should not use images deemed offensive to those injured in real mine clearing activities.

You may have to spend an extra effort in digging NFRs out as early as possible because,

  1. NFRs are easier to miss e.g., stakeholders tend to think of functional requirements first
  2. sometimes NFRs are critical to the success of the software. E.g. A web application that is too slow or that has low security is unlikely to succeed even if it has all the right functionality.

Given below are some requirements of TEAMMATES (an online peer evaluation system for education). Which one of these are non-functional requirements?

  • a. The response to any use action should become visible within 5 seconds.
  • b. The application admin should be able to view a log of user activities.
  • c. The source code should be open source.
  • d. A course should be able to have up to 2000 students.
  • e. As a student user, I can view details of my team members so that I can know who they are.
  • f. The user interface should be intuitive enough for users who are not IT-savvy.
  • g. The product is offered as a free online service.

(a)(c)(d)(f)(g)

Explanation: (b) are (e) are functions available for a specific user types. Therefore, they are functional requirements. (a), (c), (d), (f) and (g) are either constraints on functionality or constraints on how the project is done, both of which are considered non-functional requirements.