A requirement diagram documents the requirements for a system and the relationships between them. Each requirement has an identifier, a description, a risk level, and a verification method. Requirements can be linked to show derivation (one requirement stems from another) or containment (one requirement includes another).

Requirement diagrams are useful in project planning and specification work — capturing what a website, product, or service must do before any build work begins.

requirementDiagram
    requirement site_launch {
        id: 1
        text: The website must be publicly accessible
        risk: high
        verifyMethod: test
    }
    requirement user_accounts {
        id: 2
        text: Visitors must be able to create an account
        risk: medium
        verifyMethod: test
    }
    requirement email_confirmation {
        id: 3
        text: A confirmation email must be sent on sign-up
        risk: low
        verifyMethod: test
    }
    functionalRequirement secure_passwords {
        id: 4
        text: Passwords must be stored using a secure hash
        risk: high
        verifyMethod: inspection
    }

    site_launch - derives -> user_accounts
    user_accounts - contains -> email_confirmation
    user_accounts - contains -> secure_passwords

The diagram makes requirement dependencies explicit — if user_accounts changes, all the requirements it contains are affected too.