Page Source Identification

Introduction

Background

Providing navigation to static page break markers is a key accessibility feature for digital publications that are used in both print and digital formats in the same environment (e.g., classrooms). But without a means of identifying what edition of a static work the page navigation corresponds to, it is impossible for users to determine if the publication will be sufficient for their needs. For example, if a class uses a softcover edition of a book and the EPUB publication pagination corresponds to the hardcover, digital users will not be able to access the same page break locations.

How to identify the source of pagination has been a continuing problem in the EPUB 3 metadata. The original idea was to use a dc:source element [[epub-3]] to specify the pagination. This method proved unreliable both for machine verification that the EPUB creator had set the method and to extract and present the information to users. Publishers sometimes specify multiple sources for their publications in multiple dc:source elements, making it impossible for a machine to determine which identifies the source.

To address this problem, the specification then introduced a "refinement" [[epub-3]] property called source-of [[epub-3]] whose only purpose was to indicate which dc:source property identified the source.

Since its addition, however, two additional problems have surfaced with this approach:

It was defined in a way that makes it unique to EPUB 3's metadata format. When the refines attribute was nearly dropped in EPUB 3.1, it exposed that there was still no other way to express this information. Consequently, future formats cannot rely on the source-of property.
Relying on dc:source confuses how to state that a digital-only publication does not have a source for its markers. EPUB creators have resorted to identifying the current publication as the source of itself or saying that the publication has a source of nothing for the pagination, neither of which makes much sense logically and are at best hacks of the metadata. Omitting a dc:source, while accurate in this situation, makes validation difficult as it cannot be determined whether the EPUB creator simply forgot to specify the source.

The pageBreakSource property proposed in this document is intended to provide a simple and reliable solution to these problems moving forward.

Terminology

This specification uses terminology defined in EPUB 3 [[epub-3]].

Only the first instance of a term in a section links to its definition.

The `pageBreakSource` property

Definition

Name:	`pageBreakSource`
Description:	Provides a unique identifier for the source of the page break markers in an EPUB publication. The identifier should be expressed as a URN when the value conforms to a recognized scheme such as an ISBN. If a unique identifier does not exist for the source, EPUB creators should use a text description that identifies the source as clearly as possible (e.g., the title of a word processing document). If the page break markers are unique to the EPUB publication (e.g., for a digital-only edition), EPUB creators MUST specify the value "`none`".
Allowed value(s):	`xsd:string`
Cardinality:	Exactly one when the publication includes a page list and/or page break markers, otherwise 0.

Examples

In this example, the pagination corresponds to a print edition with an ISBN number. A URN is used to identify the scheme the number conforms to.

<meta
    property="pageBreakSource">
   urn:isbn:9780010010001
</meta>

In this example, the publisher has added the page break markers and page list for a digital-only edition. The value none indicates that the pagination is not drawn from another source.

<meta
    property="pageBreakSource">
   none
</meta>

In this example, the name of the document and its format are used to identify the source of the pagination.

<meta
    property="pageBreakSource">
   Hobo eReader User Manual. PDF: https://example.org/manuals/hobo/
</meta>