GB/Z 18906-2002Open electronic-book publication structure (English PDF)

Foreword

This guiding technical document is a modified adoption of the Open eBook Publication Structure (first edition) of the Open eBook Forum (Oebf). Annex B (OEB package DTD), Annex C (OEB document DTD) and Annex D (character entities) of the original document have not been adopted; for detailed information about that organization see http://www.openebook.org.

This guiding technical document is for reference only. Annex A of this guiding technical document is an informative annex.

This guiding technical document was proposed by the Ministry of Information Industry of the People's Republic of China and is under the overall jurisdiction of the China Electronics Standardization Institute.

The drafting organizations are the China Electronics Standardization Institute (CESI) and the Institute of Computing Technology of the Chinese Academy of Sciences. The main drafters are Huang Tiejun, Lin Shouxun, Xiao Ming, Li Honghui and Gao Jian.

1 Scope

The purpose of studying the structure of open electronic book publications is to provide a specification for expressing the content of electronic books. In particular: this guiding technical document attempts to give content providers, such as publishers and other persons or bodies owning displayable content, and tool providers, a minimal general guide, so as to ensure that the content of an electronic book keeps its fidelity, accuracy, accessibility and presentability on every electronic book platform; it attempts to reflect the present state of the various electronic book content format standards; and its objective is to provide publishers, agencies, authors and other publishers of electronic book content with a format that allows them to offer users electronic book content suited to many reading systems.

The premise of this guiding technical document is that, for electronic book technology to achieve greater success on the market, reading systems must be able to access a large number of works of many types conveniently.

2 Normative references

The provisions in the following documents become provisions of this guiding technical document through reference in it. For dated references, subsequent amendments (excluding corrections) or revisions do not apply; however, parties reaching agreement on the basis of this guiding technical document are encouraged to study whether the latest editions may be used. For undated references, the latest edition applies.

GB/T 7408, Data elements and interchange formats - Information interchange - Representation of dates and times (eqv ISO 8601)

GB 13000.1, Information technology - Universal multiple-octet coded character set (UCS) - Part 1: Architecture and basic multilingual plane (idt ISO/IEC 10646-1)

GB/T 17235.1, Information technology - Digital compression and coding of continuous-tone still images - Part 1: Requirements and guidelines (eqv ISO/IEC 10918-1)

3 Terms and definitions

The following terms and definitions apply in this guiding technical document.

3.1 basic OEB document - an OEB document whose structure is defined according to this guiding technical document. 3.2 content provider - a publisher, author or other information provider who supplies a publication to one or more reading systems in the format described in this guiding technical document. 3.3 deprecated - a function that this guiding technical document allows but recommends the user not to use; the function may be abandoned in a future version.

3.4 extended OEB document - an OEB document that, within the extension mechanism defined in this guiding technical document, uses constructs other than those specified in it. 3.5 OEB core media type - a MIME media type that all reading systems must support. 3.6 OEB document - an XML document conforming to this guiding technical document. 3.7 OEB package - the file describing an OEB publication; it identifies all the other files in the publication and provides description and access information about them.

3.8 OEB publication - the collection of OEB documents together with other files, the other files usually appearing as media types of various kinds including structured text and graphics, which together form the inseparable constituent parts of the publication. 3.9 reader - the person who reads the publication. 3.10 reading device - the physical platform, hardware and software, that presents the publication.

3.11 reading system - a unified whole of software and hardware able to accept an OEB publication and to make it usable by the reader. The greatest difference among reading systems may lie in the difference of their architecture. A reading system may be implemented on a single device or distributed over several computers. It is to be noted in particular that, if a reading device is part of a larger reading system, that device is not required to accept OEB publications directly, but the reading system as a whole must be able to do so. A reading system may also include other additional processing functions outside the scope of this guiding technical document, such as compression, indexing, encryption, rights management and distribution.

4 Overview

4.1 About this guiding technical document. This guiding technical document brings together publishers, reading system manufacturers, software developers and experts on the relevant standards; it is the result of a joint exploratory effort.

4.2 Relationship with other specifications. This guiding technical document combines subsets and applications of other relevant specifications, so as to make it convenient to create, organize, express and interchange electronic documents of every kind unambiguously. The relevant specifications include: a) the XML 1.0 markup meta-language (http://www.w3.org/TR/REC-xml); b) the XML namespaces specification (http://www.w3.org/TR/REC-xml-names); c) the HTML 4.0 document content markup language (http://www.w3.org/TR/REC-html40), with the XHTML 1.0 specification also taken into account (http://www.w3.org/TR/xhtml1/); d) the CSS 1 style sheet language (http://www.w3.org/TR/REC-CSS1), including also CSS 2.

Two XML DTDs are defined in this guiding technical document: the package DTD and the basic OEB document DTD. The package DTD forms the root of a complete publication, and the reading system uses it to find and organize the constituent parts of the publication; the basic OEB document DTD defines formally the HTML subset described in this guiding technical document.

4.2.2 Relationship with XML namespaces. The current version of this guiding technical document does not require the reading system to handle XML namespace prefixes according to the XML namespaces draft recommendation. A namespace prefix is a way of prefixing element and attribute names so as to distinguish names from several different definition sets. Using an XML namespace declaration, a prefix can be associated with a unique URI; a namespace declaration may also take a URL as the default namespace and apply it to elements lacking a namespace prefix. The XML namespace prefix and the element that follows it are separated by a colon. The use of namespace prefixes in OEB documents is forbidden in this guiding technical document; however, to use the various attributes of the Dublin Core metadata elements in an OEB package, forms such as dc:prefix are required.

4.2.3 Relationship with HTML. Given the importance of existing software tools, legacy data, publishing practice and market conditions, this guiding technical document is based on HTML. This approach allows content providers to explore existing HTML content, tools and specialized techniques further. To keep the development burden on reading system developers to a minimum - they may use devices restricted in power and in display - the publication structure of this guiding technical document does not include all the HTML elements and attributes. The elements and attributes are selected from the HTML 4.0 specification, following the principle of matching the direction of development of existing HTML, XHTML and emerging XML. Annex A gives a complete list of the element types in HTML 3.2, HTML 4.0 and the OEB document.

4.2.4 Relationship with CSS. This guiding technical document defines a style language on the basis of CSS 1 and CSS 2, with the media type text/x-oebl-css. Although the OEB authoring group recognized that this media type definition does not match the draft recommendation of the CSS working group, practical circumstances made it necessary. The document includes CSS-based style sheet constructs, which are used to define baseline display effect functions. To keep the burden on reading system developers and device manufacturers to a minimum, not all the properties of CSS 1 or CSS 2 are included; a few additional properties and property values are added, to support page layout, page headers and page footers.

4.2.7 MIME media types. A list of core MIME media types is defined, which all reading systems must be able to support and which every publication must include. The OEB core MIME media types are: image/jpeg (RFC 2046) for raster graphics; image/png (RFC 2083) for raster graphics; text/x-oebl-document (this guiding technical document) for basic or extended OEB documents; and text/x-oebl-css (this guiding technical document) for the OEB CSS style sheet subset.

4.3 Conformance. 4.3.1 Conformance between documents and publications. Two named conformance levels are defined for an OEB document, baseline conformance and extended conformance, and a conformance level is defined for an OEB publication. 4.3.1.1 General requirements: a conforming OEB document or package file must be a well-formed XML document as defined by the XML 1.0 specification; must begin with a correct XML declaration; must be encoded in UTF-8 or UTF-16; must use the XML empty-element syntax for empty elements, with a space before the trailing slash; must not include an internal declaration subset; and all attributes with NMTOKEN, ID or IDREF values must be legal XML names.

5 The OEB package

A publication conforming to this guiding technical document must contain one and only one OEB package file, which can be used to specify the OEB documents, graphics and other objects making up the OEB publication and how they relate to one another. To make the package files easy to recognize among the file group making up a publication, it is recommended that all package files use the same extension .opf; the MIME media type of package files is text/xml. This guiding technical document does not define explicitly how the various files are bundled together physically to produce a data interchange object, such as a .zip or .tar file.

The main constituent parts of the OEB package file are: PACKAGE IDENTITY, a unique identifier treating the OEB as a whole; METADATA, the metadata about the publication - title, author, publisher and so on; MANIFEST, a list of all the files making up the publication, including documents, graphics and style sheets, together with fallback declarations for file types not supported by this guiding technical document; SPINE, an arrangement of documents providing a linear reading order; TOURS, a set of alternative reading sequences for the publication, for instance selectable views for different reading purposes and for readers of different levels of skill; and GUIDE, a series of pointers to the basic structure of the publication, such as its contents, foreword and table of contents.

The OEB package must be a valid XML document conforming to the OEB package DTD. 5.1 Package identity. The package element is the outermost element in the package file, and all the other elements are nested within it. The OEB package must specify a value as its unique-identifier attribute; that value is used to specify which dc:Identifier element provides the preferred or primary identifier of the package. The author of the package file is responsible for choosing a primary identifier that is unique for that particular package and unique only for it.

5.6 Guide. A guide element may exist in the package, containing one or more reference elements. The guide element can identify the basic structure of the constituent parts of the publication, so making it convenient for the reading system to access them. The constituent parts of an electronic book may be pointed to the table of contents, the list of illustrations, the foreword, the bibliography and many other standard constituent parts. This guiding technical document does not require the reading system to use the guide element in any way. Each reference part must have an href attribute pointing to an OEB document contained in the manifest. The required type attribute describes the component of the publication the href points to; in application, the value of the type attribute must be chosen from the list given, which is taken from the thirteenth edition of the Chicago Manual of Style: cover, title page, toc, index and so on. If other type attributes are needed, their names must begin with the string other.

6 OEB document elements and attributes

6.6 The anchor element. 6.6.1 name (deprecated): this attribute provides an address for a hypertext link. HTML 4.0 and this guiding technical document deprecate it and recommend the id attribute instead; HTML 4.0 allows any string as its value, while this guiding technical document restricts the value to a legal XML name. 6.6.2 href: this attribute states the target URI (Uniform Resource Identifier) of the link element. If the target the URI points to is not an OEB core media type, a fallback must be provided in the OEB core media type list; otherwise the content behind the link cannot be presented by the reading system. 6.6.3 rel, rev: the rel attribute expresses the relationship between the current document and the linked document, while rev is the converse, defining the relationship of the linked document to the current one. 6.6.4 charset, type, hreflang, accesskey, shape, coords, tabindex, onfocus, onblur: this guiding technical document ignores these attributes.

6.7 The area element. 6.7.1 shape specifies the shape of the region; the possible shapes are rect, a rectangle, the default value, defined by the coordinates of the top left and top right corners; circle, defined by the coordinates of the centre and the radius; poly, a polygon built from a series of coordinate pairs, all the coordinates being joined in an ordered list with the last pair joined to the first; and default, the default type (rectangle), which may also be set explicitly to a rectangle. 6.7.2 coords defines the comma-separated coordinates of a shape, the values depending on the value of the shape attribute. 6.7.3 href states the target URI of the hot-spot link on the image map. 6.7.4 nohref indicates that the image region has no associated hyperlink. 6.7.5 alt provides an alternative text string for a text browser, expressing the URI of the image map in a form easier to read. 6.7.6 tabindex, accesskey, onfocus, onblur: ignored.

6.8 The b element is fairly common in HTML documents; it is better to set the CSS font-weight property to bold or to use the HTML strong element. 6.9 The base element is used to handle links in an OEB document. 6.9.1 href defines a base URI for the relative URIs elsewhere in the document. 6.9.2 id, style, class, title: HTML 4.0 and this guiding technical document do not support these attributes.

7 The OEB CSS style subset

7.2 border describes the mixture of style, width and colour of all four borders of an element; the description does not require support for coloured borders. The reading device must be able to recognize all the following style keywords, but may, following the rules of the CSS 1 core, choose to map any style other than none to solid: none (the default value, assumed when no style is specified), solid, dotted, dashed, double, groove, ridge, inset and outset, the last seven of which may be mapped to solid by the reading system. Except for img, object and table, the reading system is not required to generate borders. The reading system must recognize all the following width values: thin, medium (the default value) and thick, together with absolute widths; it need not generate three different widths for the three keyword values, and may for instance map any non-zero absolute width to one pixel. Note: the reading system must recognize for border the same colour set as for background-color and color (see 7.1 above), but need not actually distinguish them in display.

7.3 clear provides the same effect as the deprecated br clear attribute; the possible values are none (the default), left, right and both.

7.4 display (values changed). Various values are defined for this property in CSS 1, and CSS 2 adds more. The reading system must refer to the values block, inline and none of CSS 1. This guiding technical document also defines two new values, oeb-page-head and oeb-page-foot. Any content intended to be described as a page header or page footer may be marked by assigning these values to the display property. The content of an element assigned display: oeb-page-head can be described only as a page header, and that of an element assigned display: oeb-page-foot only as a page footer; neither can simply be handled as if it were inline or block. However, in certain special cases, in order to present the page better, the reading system is free to handle headers and footers, or to display them in another way; for instance a device with only a very small screen may disregard them altogether.