Introduction to OPF Metadata

The OPF file contains a lot of important metadata, including basic information about the book, accessibility metadata, and evaluation and conformance metadata! This resource discusses what to include, and how to include it.

  • Subject(s):

    Ebook Production

  • Resource Type(s):

    Step-by-Step

  • Audience:

    Introduction

Suggested Prerequisites

Before reading this, you might want to read:

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).

Required?ValueMeaningCode for EPUB 3
One of rows 1-3 is required to see EPUB Accessibility Specification 1.0http://www.idpf.org/epub/a11y/accessibility-20170105.html#wcag-aThe EPUB Publication meets all accessibility requirements and achieves [WCAG 2.0] Level A conformance. <link rel="dcterms:conformsTo" href="http://www.idpf.org/epub/a11y/accessibility-20170105.html#wcag-a"/>
http://www.idpf.org/epub/a11y/accessibility-20170105.html#wcag-aaThe EPUB Publication meets all accessibility requirements and achieves [WCAG 2.0] Level AA conformance. <link rel="dcterms:conformsTo" href="http://www.idpf.org/epub/a11y/accessibility-20170105.html#wcag-aa"/>
http://www.idpf.org/epub/a11y/accessibility-20170105.html#wcag-aaaThe EPUB Publication meets all accessibility requirements and achieves [WCAG 2.0] Level AAA conformance. <link rel="dcterms:conformsTo" href="http://www.idpf.org/epub/a11y/accessibility-20170105.html#wcag-aaa"/>
One of these is required to meet the EPUB Accessibility Specification 1.1 (which is not yet final).EPUB-A11Y-11_WCAG-20-AMeets EPUB Accessibility 1.1 Specification and WCAG 2.0 at Level A<meta property="dcterms:conformsTo"
id="conf">
EPUB-A11Y-11_WCAG-20-A</meta>
EPUB-A11Y-11_WCAG-20-AAMeets EPUB Accessibility 1.1 Specification and WCAG 2.0 at Level AA<meta property="dcterms:conformsTo"
id="conf">
EPUB-A11Y-11_WCAG-20-AA</meta>
EPUB-A11Y-11_WCAG-20-AAAMeets EPUB Accessibility 1.1 Specification and WCAG 2.0 at Level AAA<meta property="dcterms:conformsTo"
id="conf">
EPUB-A11Y-11_WCAG-20-AAA</meta>
EPUB-A11Y-11_WCAG-21-AMeets EPUB Accessibility 1.1 Specification and WCAG 2.1 at Level A<meta property="dcterms:conformsTo"
id="conf">
EPUB-A11Y-11_WCAG-21-A</meta>
EPUB-A11Y-11_WCAG-21-AAMeets EPUB Accessibility 1.1 Specification and WCAG 2.1 at Level AA<meta property="dcterms:conformsTo"
id="conf">
EPUB-A11Y-11_WCAG-21-AA</meta>
EPUB-A11Y-11_WCAG-21-AAAMeets EPUB Accessibility 1.1 Specification and WCAG 2.1 at Level AAA<meta property="dcterms:conformsTo"
id="conf">
EPUB-A11Y-11_WCAG-21-AAA</meta>

Evaluator Information

This is required to meet the EPUB Accessibility Specification 1.0

Property — ally:certifiedBy
Required?ValueMeaningCode for EPUB 3
This is required to meet the EPUB Accessibility Specification 1.0Name of third party certifier or publisher, if they have self-certified.Affirms that publication has been evaluated by a third party certifier or the publisher (i.e., self-certified).<meta property="a11y:certifiedBy">Third Party File Certifier OR Name of Publisher</meta>
This is optional for both EPUB Specifications (1.0 and 1.1).Name of credentialing authorityIndicates that the party that certifies the content has been issued a credential or badge that establishes their authority to certify content accessible.<meta property="a11y:certifierCredential">Name of Credential</meta>

Optional addition (link to credential source): <link rel="a11y:certifierCredential" href="urlOfCredential"/>
This is optional for both EPUB Specifications (1.0 and 1.1).Link to the certifier’s report (if available)Directs people to the full certification report, if available<link rel="a11y:certifierReport"
href="
urlOfReport"/>
This is required to meet the EPUB Accessibility Specification 1.1 (which is not yet final).Name of third party certifier or publisher, if they have self-certified.Affirms that publication has been evaluated by a third party certifier or the publisher (i.e., self-certified).<meta property="a11y:certifiedBy" refines="#conf" id="certifier">Third Party File Certifier OR Name of Publisher</meta>
This is optional for both EPUB Specifications (1.0 and 1.1).Name of credentialing authorityIndicates that the party that certifies the content has been issued a credential or badge that establishes their authority to certify content accessible.<meta property="a11y:certifiedBy" id="certifier">Accessibility Testers Group</meta>
This is optional for both EPUB Specifications (1.0 and 1.1).Link to the certifier’s report (if available)Directs people to the full certification report, if available<link rel="a11y:certifierReport" refines="#certifier" href="urlOfReport/"/>
This is optional for both EPUB Specifications (1.0 and 1.1).Date of the evaluationProvides the date of the evaluation.<meta property="dcterms:date" refines="#certifier">20xx-xx-xx</meta>

Checklist for OPF Metadata

There is a lot of information on this page! But what you actually need to include in your OPF is simple; this checklist should help out!

Note: there are many more optional Dublin Core properties than are included in this table.

TypeItemDescriptionRequired
Dublin Core Metadatadc:title
TitleYes
dc:identifierIdentifierYes
dc:language
LanguageYes
dcterms:modifiedLast modifiedYes
dc:creatorAuthorNo
dc:datePublication dateNo
dc:publisherPublisherNo
dc:contributorContributor (editor, translator, etc.)No
dc:subjectBook subject(s)No
Schema.org Accessibility Metadataschema:accessibilitySummaryAccessibility SummaryYes
schema:accessMode*Access ModeYes
schema:accessModeSufficient*Sufficient Access ModeNo
schema:accessibilityFeature*Accessibility FeatureYes
schema:accessibilityHazard*Accessibility HazardYes
Conformance & Evaluation Metadatadcterms:conformsToThe standards and specification the EPUB conforms toYes
a11y:certifiedByThe certifier (third party or publisher)Yes
a11y:certifierCredentialThe credential of the certifierNo
a11y:certifierReportThe certification reportNo
dcterms:date**The date of the evaluation.No
*These items may have more than one value
**In EPUB 1.1 Specification, only.

Next Steps

1

Understanding and Creating Schema.org Metadata for Ebooks

Introduction to Accessibility Metadata for Ebooks

Accessibility metadata should be included with every ebook, as it lets the reader know about what accessibility features have been included! This introduction discusses the importance of accessibility metadata, and shares examples of each type.

Subject(s): Metadata
Resource Type(s): Standards and Best Practices
Audience:
Technical
2

Creating Accessibility Metadata for an ONIX Record

Introduction to ONIX Metadata for Ebooks (and the Supply Chain)

This resource discusses the importance of ONIX accessibility metadata, and shares an example of the accessibility section of an ONIX file.

Subject(s): Metadata
Resource Type(s): Foundations and Rationale, Standards and Best Practices
Audience:
Technical

External Links to More Information

DCMI Metadata Terms

The Dublin Core Metadata Innovation is an organization supporting innovation in metadata design and best practices across the metadata ecology. This page shares all the possible Dublin Core terms you may want to use in your book’s OPF file.

EPUB Accessibility 1.0

This specification discusses discovery and accessibility of EPUB publications. Discovery relates to accessibility metadata. Accessibility includes guidelines in WCAG 2.0 and some additional items on page navigation and media overlays. The specification also discusses how to indicate conformance, information about optimized publications for specific use cases such as audiobooks, and a short section on distribution considerations.

EPUB Accessibility 1.1

This specification (which is still in draft format as of May, 2022) discusses discovery and accessibility of EPUB publications. Discovery relates to accessibility metadata. Accessibility includes guidelines in WCAG 2.0 and some additional items on page navigation and media overlays. The specification also discusses how to indicate conformance, information about optimized publications for specific use cases such as audiobooks, and a short section on distribution considerations.

EPUB Packages 3.2

This specification lays out the technical requirements for an EPUB Package, including what is required in the “Package Document”, also known as the OPF file (content.opf). This specification also details the requirements of the EPUB Navigation Document (a machine- and human-readable document—usually toc.xhtml or nav.xhtml—that provides navigation aids such as the table of contents.