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4- METADATA
4.1- DJVULIBRE METADATA
DjVuLibre has introduced metadata annotations a few years ago.
Metadata entries for each page are represent by key/value pairs
located in a metadata directive in the annotation chunk.
Metadata entries for the document are represented similarly
using the methods described in the next section.
The metadata directive has the form
(metadata ... (key "value") ... )
Each entry is identified by a symbol <key>
representing the nature of the metadata entry.
The string <"value"> represents
the value associated with the corresponding key.
Several sets of keys are noteworthy.
* Keys borrowed from the BibTex bibliography system.
These key names are always expressed
in lowercase, such as 'year', 'booktitle', 'editor',
'author', etc.
* Keys borrowed from the PDF DocInfo.
These key names start with an uppercase letter:
'Title', 'Author', 'Subject', 'Keywords', 'Creator',
'Producer', 'Trapped', 'CreationDate', and 'ModDate'.
The values associated with the last two keys
should be dates expressed according to RFC 3339.
4.2- XMP METADATA
The XMP specification describes a general purpose RDF/XML format for
metadata. Just like DjVuLibre metadata, XMP metadata is embedded in
an annotation chunk at the page or document level using the following
annotation directive
(xmp "<rdf:RDF xmlns:rdf=... [escaped XMP here] ...</rdf:RDF>")
The sole argument of the xmp directive is the serialized XMP data
without the "xpacket" wrapper. The "x:xmpmeta" element may also be
dropped. Only elements from "rdf:RDF" inwards are needed.
Since the XMP data is represented as a string, doublequotes and
backslashes must be escaped. Other characters may be escaped as well
(see section 2 above).
The full XMP specification is available from Adobe:
http://www.adobe.com/devnet/xmp/
To maximize interoperability with current viewers, it is recommended
that XMP manipulation programs keep the DjVuLibre metadata in sync.
This is facilitated by synchronizing the PDF DocInfo keys with XMP
properties as follows:
DocInfo key XMP property
------------ ---------------
Title dc:title
Author dc:creator
Subject dc:description
Keywords pdf:Keywords
Producer pdf:Producer
Trapped pdf:Trapped
Creator xmp:CreatorTool
CreationDate xmp:CreateDate
ModDate xmp:ModifyDate
4.3- DOCUMENT ANNOTATIONS AND METADATA
The above schemes provide ways to specify metadata for each page.
But it is often useful to provide metadata that applies to the whole
document. Document wide metadata are represented using one or
several metadata directives in the shared annotations chunk.
This scheme has a potential drawback. Since the shared annotations
is included by all pages, the document wide metadata also appears as
page metadata for all pages. This might not be adequate for some
uses. As a workaround, the djview4 viewer only displays
page metadata that differ from the document metadata.
A more definitive answer would be the definition of a document
annotation chunk located after the DIRM chunk and before any
component file. This space is already used by the NAVM chunk.
This is being considered.
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