Understanding WCAG 2.0

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Appendix C Understanding Metadata

This section discusses metadata techniques that can be employed to satisfy WCAG 2.0 Success Criteria. For more information about metadata see resources below.

At its most basic level, metadata is essentially 'data about data' and is used to both describe and find resources.

Metadata is a powerful tool that can be used for describing Web pages and accessible components of Web pages as well as associating alternate versions of Web content to each other. These descriptions in turn allows users to locate specific information they need or prefer.

In conjunction with WCAG, metadata can play a number of roles including:

  1. Metadata can be used to associate conforming alternate versions of Web pages with Web pages which do not conform, in order to allow users to find the conforming alternate version when they land on a non-conforming page that they cannot use.

  2. Metadata can be used to locate and also to describe alternate pages where there are multiple versions of a page which have been developed, especially where the alternate pages are optimized for individuals with different disabilities. The user can use the metadata both to locate the alternate versions and to identify characteristics of the versions, so that they can find the one that best meets their needs.

  3. In addition to being used for whole pages (as in #1 and #2 above), metadata can be used to describe alternate versions of subcomponents of a page. Again, the metadata can be used to find alternate versions of a Web page component as well as to get descriptions of the alternate versions ( if there are several) in order to determine which one would best meet the user's needs.

Metadata Resources

Metadata descriptions often provide values from defined, agreed vocabularies such as the resource's subject matter or its date of publication, and are machine readable - software that understands the metadata scheme in use can do useful tasks not feasible otherwise. Typically, an object having metadata may have one or more such metadata descriptions.

Well-known specifications (schemas) for metadata include:

There are some tools available to provide resource descriptions, or they can be provided manually. The more easily the metadata can be created and collected at point of creation of a resource or at point of publication, the more efficient the process and the more likely it is to take place.

Some examples include:

Accessibility metadata implementations include: