Accessibility metadata principles

Accessibility metadata Is available in different kinds of markup for different purposes. Schema.org metadata is embedded in Web pages to support search for a wide range of use cases. It can also be included in EPUB packages. Schema.org metadata can be expressed in Microdata, RDFa, or JSON-LD.

ONIX metadata is used in trade publications for the retail supply chain. ONIX uses custom markup. MARC 21 markup is used by libraries. It also uses custom markup. This paper focuses on Schema.org and EPUB, but some resources for ONIX and MARC21 are included.

Accessibility metadata can be used in three different ways. If the publication being described is not fully accessible, it is important to document its contents and any access features that are included. If the publication is fully accessible, this is a great feature to promote. And if the publication is highly accessible for some readers but inaccessible for others, such as a braille book or audio book, it is important to communicate that both to users who want that format and those who can't use it at all. These approaches use metadata to help readers find books that suit them and help readers avoid books they can't use.

EPUB carries metadata inside the publication as "package metadata." Linked metadata is also permitted in EPUB but must be implemented carefully. The precedence given to linked records vs. any embedded metadata varies depending on the version of EPUB. Use of Schema.org metadata inside the package is required to meet the EPUB Accessibility 1.0 conformance requirements. A few Dublin Core and custom fields are also used.

There are three kinds of EPUBs defined in the EPUB Accessibility 1.0 document.

  1. Discoverable — meets the discovery metadata requirements of the specification but does not meet the accessibility requirements

  2. Accessible — meets all discovery, WCAG 2.0, and EPUB accessibility requirements

  3. Optimized — meets the discovery requirements for optimizations

As described above, these three types of documents use accessibility metadata in different ways. Each type has required and recommended or optional fields.

Discoverable documents

Discoverable documents require discovery metadata, including these fields from Schema.org:

  • Required:

    • accessMode: lists the types of media included: auditory, tactile, textual, visual

    • accessibilityFeature: lists accessibility features such as video captions or image descriptions

    • accessibilityHazard: lists any hazards such as flashing light or motion simulation

    • accessibilitySummary: a human readable summary

  • Recommended:

    • accessModeSufficient: describes all the ways the publication can be used. See examples later in this paper.

  • Optional:

    • accessibilityAPI and accessibilityControl: information about interactive features for embedded applications such as simulations; these are optional since many publications don't include any interactive components. When included in an EPUB package, this metadata does not describe the features of the reading software, only of any interfaces within the publication. However, these fields can be used in other ways to describe any software including reading systems.

Accessible documents

Publications claiming conformance with accessibility standards must include discovery metadata and these additional fields:

  • Required:

    • Dublin Core metadata

      • conformsTo: states the WCAG conformance level met

    • A11y metadata (custom to EPUB Accessibility 1.0)

      • certifiedBy: states the identity of the organization making the conformance claim (publisher or testing service)

  • Optional:

    • A11y metadata (custom to EPUB Accessibility 1.0)

      • certifierCredential: identify the certifier's credentialing body

      • certifierReport: link to the certification report

Optimized documents

Optimized publications, designed to be accessible to some users but not to others, must include discovery metadata and these additional fields:

  • Required:

    • Dublin Core metadata

      • conformsTo: states the optimization standard followed, such as DAISY Audio or Braille Ready File (BRF)

  • Recommended:

    • Schema.org metadata

      • accessibilitySummary: a human-readable description of the publication and which audiences will and will not be able to use it

Accessibility metadata in action

Accessibility metadata can be used to support simple or advanced search processes. The simplest method of search is to find resources that contain a specific accessibility feature. For example, if a user who is Deaf or hard of hearing is searching for videos, they may filter for only videos that include closed captions. However, when searching a body of resources of various types, including text documents, images, and videos with and without sound, a more complex matching algorithm can take advantage of metadata about the resources and user preferences to give a more complete set of search results. This process is illustrated in the video demonstration available at: http://www.a11ymetadata.org/accessibility-metadata-in-action-at-teachers-domain/.

Accessibility metadata examples in Schema.org JSON-LD markup

Example 1: Graphic novel

This graphic novel does not have any accessibility features built in. As a result, it can only be used by readers who can read the text and look at the visual elements. Note that accessModeSufficient has only one entry. 

<script type="application/ld+json">
{
"@context": "http://schema.org/",
"@type": "Book",
"name": "Some graphic novel",
"accessMode": ["textual", "visual"],
"accessModeSufficient": [
{
"@type": "ItemList",
"itemListElement": ["textual", "visual"],
"description": "Text and images"
}
],
"accessibilitySummary": "Visual elements are not described."
}
</script>

Example 2: Video

This video has captions (a visual presentation of the dialog and sound effects) and audio description (an audio track describing important visual features). It can be used in three different ways, for example by a person without disabilities who will listen to the soundtrack and watch the visuals, by a person who is Deaf or hard-of-hearing, who will look at the visuals and read the captions, and by a person who is blind or visually impaired, who will listen to the soundtrack and the audio description. The three entries in accessModeSufficient describe these use cases. 

<script type="application/ld+json">
{
"@context": "http://schema.org/",
"@type": "Movie",
"accessMode": ["auditory", "visual"],
"accessibilityFeature": ["audioDescription", "captions"],
"accessModeSufficient": [ 
{
"@type": "ItemList",
"itemListElement": ["auditory", "visual"],
"description": "Watch and listen"
},
{
"@type": "ItemList",
"itemListElement": ["textual", "visual"],
"description": "Watch with closed captioning"
},
{
"@type": "ItemList",
"itemListElement": ["audio"],
"description": "Listen with audio description"
}
],
"accessibilitySummary": "Captions provided in English; short scenes in French have English subtitles instead."
}
</script>

Example 3: Journal article

This exemplary journal article includes descriptions of all images included in the article. 

<script type="application/ld+json">
{
"@context": "http://schema.org/",
"@type": "Article",
"name": "Journal article",
"accessMode": ["textual", "visual"],
"accessibilityFeature": ["alternativeText"],
"accessModeSufficient": [
{
"@type": "ItemList",
"itemListElement": ["textual", "visual"],
"description": "Text and images"
},
{
"@type": "ItemList",
"itemListElement": ["textual"]
"description": "Text and images"
}
],
"accessibilitySummary": "All diagrams, charts, and other visual elements are described."
}
</script>

Example 4: illustrated novel

Note in this example that the accessibility summary is used to explain how the visuals are and are not described in the alternative text. This book can be read in a number of ways, thus the long list of accessModeSufficient entries. 

<script type="application/ld+json">
{
"@context": "http://schema.org/",
"@type": "Book",
"name": "Alice in Wonderland",
"accessMode": ["auditory", "textual", "visual"],
"accessibilityFeature": ["alternativeText", "synchronizedAudioText"],
"accessModeSufficient": [
{
"@type": "ItemList",
"itemListElement": ["textual"], 
"description": "See the text"
},
{
"@type": "ItemList",
"itemListElement": ["textual", "visual"], 
"description": "See the text and images"
},
{
"@type": "ItemList",
"itemListElement": ["auditory"], 
"description": "Hear the text and image descriptions"
},
{
"@type": "ItemList",
"itemListElement": ["auditory", "visual"], 
"description": "Hear the text and see the images"
},
{
"@type": "ItemList",
"itemListElement": ["auditory", "visual", "textual"], 
"description": "Hear the text; see the text and images"
}
],
"accessibilitySummary": "Short descriptions are provided; long descriptions of the images are not needed for most readers."
}
</script>

Tools and Resources

Tools for accessible EPUB

Resources for accessible EPUB

Resources for ONIX

Resources for MARC21

Madeleine Rothberg

Senior Subject Matter Expert

The Carl and Ruth Shapiro Family National Center for Accessible Media at WGBH

Madeleine Rothberg is a Senior Subject Matter Expert at the National Center for Accessible Media at WGBH. She focuses on providing access to multimedia and information technology both through directly accessible solutions such as captions, talking software, and audio description, and through improvements to infrastructure such as interoperability standards. Madeleine is active in EPUB accessibility, co-chaired the IMS Global Accessibility Working Group, and contributed to the accessibility metadata effort for Schema.org. Personal health records, digital libraries, assessment questions, STEM textbooks — we can improve them all with accessibility and usability.