wiki:interaction-design/conceptual-model

Version 56 (modified by nhoyt, 6 years ago) (diff)

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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 element name (or wildcard denoting any element) and one or more optional predicates, e.g. input[type="text"]
  2. target resources: a set of web resources defined by one or more element definitions

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
  4. ruleset: a collection of rule mappings tailored for a particular audience and based on a set of standard requirements (e.g. WCAG 2.0)

D. Evaluation actions and results

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

Further breakdown of evaluation objects

accessibility rule

  • id: unique identifier for the rule (referenced by rule mappings and rule results)
  • scope: "element" or "page"
  • target resources: the set of web resources to which this rule applies
  • resource properties: the specific properties of the target resources that pertain to the rule definition
  • definition: the markup patterns or requirements that must be present in, or met by, the target resources
  • summary: a concise or abbreviated statement of the rule definition
  • purpose: the significance of the rule for users with disabilities
  • techniques: the specific markup patterns that are required or recommended for passing the rule; may be empty if covered by the rule definition
  • 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
  • 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

rule category

  • a grouping of rules with related accessibility requirements or target resources
  • 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
  • informational links: links to further documentation re. the set of rules and their relationships

rule mapping

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

ruleset

  • a collection of rule mappings tailored for a particular audience and based on a set of standard requirements (e.g. WCAG 2.0)
  • 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

node result

  • id: identifier of the accessibility rule that was applied to obtain this result
  • node result value: one of the evaluation result values defined above or "hidden"
    • for example, for rules with "element" scope, the node-level result value may be "hidden" indicating that the node was not visible to assistive technologies
  • resource properties and their values at the node level as applicable

rule result

  • id: identifier of the accessibility rule that was applied to obtain this result
  • node results: the set of node results used in the overall determination of the page result
  • page result value: one of the evaluation result values defined above
  • resource properties and their values at the node and/or page level as applicable

summary result

  • at lowest level, a single rule result
  • aggregation of rule results by web resource objects:
    • node: all results for all rules that apply to a particular node; all results for all rules that apply to a set of nodes (e.g. all images)
    • page: all results for all page-level rules; all results for all node-level rules that apply to any nodes 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