wiki:interaction-design/conceptual-model

Conceptual Model | Data Objects | Getting Started

Conceptual Model for Web Accessibility Evaluation

A conceptual model describes all of the objects, actions and concepts, and their relationships within a system.

This conceptual model also serves as the foundation for  the conceptual model for web accessibility coding practices.

A. Web resource objects

  1. element: an HTML element, its attributes and properties
  2. page: an HTML document, including its top-level element

B. Web resource definitions

  1. element definition: an HTML element name (or wildcard denoting any element) and an optional predicate, e.g. input[type="text"]
  2. target elements: the set of HTML elements defined by one or more element definitions
  3. target resources: the set of web resources to which a rule is applied (typically target elements but may also include the top-level page)

C. Evaluation objects

  1. accessibility rule: the requirements that one or more target resources must meet
  2. rule category: a grouping of rules with related accessibility requirements or target resources
  3. rule mapping: the membership properties of an accessibility rule within a ruleset (e.g. whether a rule is required or recommended)
  4. ruleset: a collection of rule mappings tailored for a particular audience and with a set of standards compliance goals (e.g. WCAG 2.0)

D. Evaluation actions and results

  1. rule evaluation: the application of an accessibility rule to its target resources
  2. result value: one of the following: violation, warning, pass, manual check, not applicable
    • a rule mapping specifies whether a rule is required or recommended
    • violation is the result value when a required rule fails
    • warning is the result value when a recommended rule fails
    • pass, manual check and not applicable values are common to both required and recommended rules
  3. element result: the result of a rule evaluation with respect to one of its target elements
  4. rule result: the aggregate result of a rule evaluation with respect to its target resources (all of its target elements and/or the entire page)
  5. summary result: an aggregation of element and/or rule results (organized and quantified in various ways, e.g. percentage of pass results)

Further breakdown of evaluation objects

accessibility rule

  • title: a concise or abbreviated statement of the rule definition
  • definition: the markup patterns or requirements that must be present in, or met by, the target resources
  • target resources: the set of web resources to which this rule applies
  • scope: element or page: specifies the level of the target resources (which affects how the rule result is calculated and reported)
  • purpose: an explanation of why the rule is important
  • techniques: the specific markup patterns that are required or recommended for passing the rule
  • manual checks: the list of questions the user needs to ask when performing a manual check
  • corrective action: concise description of what needs to be done to remedy a failure or perform a manual check
  • element properties: the specific properties of the target elements to which the rule definition pertains
  • category: the rule category to which the rule belongs
  • primary requirement id: reference to the most pertinent WCAG 2.0 Success Criterion for this rule
  • related requirement ids: list of references to other WCAG 2.0 Success Criteria, ordered by pertinence
  • language dependency: the languages upon which the rule depends, if any
  • informational links: links to examples, articles or other resources relating to the rule definition and/or techniques
  • last updated: date of most recent changes
  • id: unique identifier for the rule (referenced by rule mappings, element results and rule results)

rule category

  • a grouping of rules with related accessibility requirements or target resources
  • informational links: links to further documentation re. the set of rules and their relationships
  • examples of categories based on rules related by accessibility requirements: Color Contrast, Landmarks, Language
  • examples of categories based on rules related by target resources: Images/Media, Controls, Headings, Links, Lists, Tables, Abbr/Acronym

rule mapping

  • type: required or recommended
  • enabled: true or false
  • rule id: identifier of the accessibility rule to which the above properties are being mapped

ruleset

  • a collection of rule mappings tailored for a particular audience and with a set of standards compliance goals (e.g. WCAG 2.0, Levels A & AA)
  • Note: via rule mappings, the rule type (required or recommended) for any given rule can vary from one ruleset to another
  • Note: via rule mappings, one ruleset may include rules that other rulesets omit and vice versa (using the "enabled" property)

Further breakdown of evaluation results

element result

  • the element name and its document position
  • the result value at the element level
  • a result message, including a corrective action when appropriate
  • pertinent element properties and values, which may help identify the element
  • Note: the element result value may be one of the evaluation result values defined above or hidden
    • for example, for rules with element scope, the element-level result value may be hidden, indicating that the element was not visible to assistive technologies
  • rule id: identifier of the accessibility rule that was applied to obtain this result

rule result

  • the result value at the rule level
  • a result message, including a corrective action when appropriate
  • the set of element results used in the overall determination of the rule result
  • page-level properties and their values as applicable (when the rule has page scope)
  • rule id: identifier of the accessibility rule that was applied to obtain this result

summary result

  • at the lowest level, a single rule result
  • aggregation of rule results by web resource objects:
    • element: all results for all rules that apply to a particular element; all results for all rules that apply to a set of elements (e.g. all images)
    • page: all results for all page-level rules; all results for all element-level rules that apply to any elements on the page
  • aggregation of rule results at page level by WCAG success criteria
  • aggregation of rule results at page level by WCAG Level (A, AA, AAA)
  • aggregation of rule results at page level by rule type (required, recommended)
  • a list of all rules that were not evaluated (enabled = false)

Additional resources