Introduction to OPF Metadata

Suggested Prerequisites

Before reading this, you might want to read:

• Introduction to EPUB Files
• Introduction to the OPF File

Introduction to OPF Metadata

The OPF file contains a metadata section, which shares important information about the book. There are two main types: Dublin Core metadata, and accessibility metadata.

Note that the metadata in the OPF is different from the metadata that you might send via an ONIX feed, or fill out in an Excel template.

Dublin Core Metadata

There is Dublin Core Metadata, which shares the most basic details about the book. The “EPUB Packages 3.2” Specification document, which details all of the semantics and conformance requirements required for an EPUB states that there are only four required pieces of Dublin core metadata: Title, Identifier, Language, and the date the file was last modified. But of course, it is good to have a few additional pieces! Including the four required pieces, an OPF file for an ebook should always have the following Dublin Core metadata:

• Title: <dc:title>The Title of the Book</dc:title>
• Publication date: <dc:date>2017-06-01</dc:date>
• Identifier (usually ISBN): <dc:identifier id="bookid">9781234567890</dc:identifier>
• Language of the book: <dc:language>en-CA</dc:language>
• Author: <dc:creator>Author Name</dc:creator>
• Date of last modification: <meta property="dcterms:modified">2018-02-19T14:33:21Z</meta>

Many more Dublin Core metadata elements are available, like the following, to share a few: 

• Publisher: <dc:publisher id="publisher">Publisher Name</dc:publisher>
• Contributor, which can be used for translators, illustrators, etc: <dc:contributor id="translator">Translator name</dc:contributor> (note that you can put any role in the id attribute, which here says “translator”)
• Subject information: <dc:subject id="subject-1">Space ships — Fiction</dc:subject> (note that you can have multiple subjects, just ensure that they have unique IDs, like if this book also had <dc:subject id="subject-2">Moon — Fiction</dc:subject>

If your book has pagination, and the pagination reflects a print source, this information should be included like so:

• <dc:source id="src-id">urn:isbn:9781234567890</dc:source>
• <meta refines="#src-id" property="source-of">pagination</meta>

To learn more about the available Dublin Core metadata elements, check out the External Links to More Information below.

Accessibility Metadata

There are two types of accessibility metadata which should be included in the OPF file of an EPUB.

• Schema.org accessibility metadata
• Conformance/evaluation metadata, which is included in the OPF file, and can also be included in the ONIX file.

Schema.org accessibility metadata

Schema.org accessibility metadata is discussed in depth in another resource – see the Next Steps section below. But we’ll include a sample set here! 

Here is an example of a set of Schema.org accessibility metadata you might find in an EPUB:

<meta property="schema:accessMode">textual</meta>
<meta property="schema:accessMode">visual</meta>
<meta property="schema:accessModeSufficient">textual</meta>
<meta property="schema:accessModeSufficient">textual,visual</meta>
<meta property="schema:accessibilityFeature">alternativeText</meta>
<meta property="schema:accessibilityFeature">readingOrder</meta>
<meta property="schema:accessibilityFeature">structuralNavigation</meta>
<meta property="schema:accessibilityFeature">tableOfContents</meta>
<meta property="schema:accessibilityHazard">Sound</meta>
<meta property="schema:accessibilityHazard">noFlashingHazard</meta>
<meta property="schema:accessibilityHazard">noMotionSimulationHazard</meta>
<meta property="schema:accessibilitySummary">This publication is screen reader friendly and is accessible to users of assistive technology. It was created with accessibility in mind. There are image descriptions, a page list, and detailed navigation/structure. There are no accessibility hazards like sound or flashing. It meets the Web Content Accessibility Guidelines (WCAG), Level "AA".</meta>

Conformance/evaluation metadata

Conformance and evaluation metadata are metadata that need to be included in order to meet the EPUB Accessibility Specification. The OPF needs to include one of the “dcterms:conformsTo” properties (whichever one is applicable), and an “a11y:certifiedBy” property, whether the book was certified by a third party, or if it was done by the publisher themself. There are a few optional pieces as well: “a11y:certifierCredential”, which shares the credentials of the certifier; “a11y:certifierReport”, which links to the evaluation report if it is available; and “dcterms:date”, which indicates the date of the evaluation.

Here is an example of some conformance and evaluation metadata for a hypothetical book that was certified by Benetech:

<link rel="dcterms:conformsTo" href="http://www.idpf.org/epub/a11y/accessibility-20170105.html#wcag-aa"/>
<meta property="a11y:certifiedBy">Benetech</meta>
<meta property="a11y:certifierCredential">https://bornaccessible.org/certification/gca-credential/</meta>

The following tables break down all of the potential options for what you can include in your conformance and evaluation metadata.

Publication Conformance

One of these is required to meet the EPUB Accessibility Specification 1.0 or the EPUB Accessibility Specification 1.1 (which is not yet final).

Evaluator Information

This is required to meet the EPUB Accessibility Specification 1.0