ZedAI Primer: Metadata
From zedwiki
Contents
- 5.1. Referencing metadata in external resources
- 5.2. Making the document itself the metadata resource
As described in Section 1.5, “Metadata”, all Z39.98-AI documents must contain the metadata items identifier, publisher, and date (the latter also serving as a version identifier). This is an intentionally minimal set of metadata items, which serves only to uniquely identify the document and its publisher.
In many circumstances, it is of course necessary to be able to express more and richer metadata about the document (and, in the case of republishing, about the document source, e.g. the work being republished). Given that various metadata expression languages exist in the world today, and given that different Z39.98-AI usage domains have different needs and requirements in terms of metadata, there is a certain amount of flexibility available with regards to how this "richer" metadata can be expressed in Z39.98-AI documents.
5.1 Referencing metadata in external resources
The key principle is that metadata resources can be external to the Z39.98-AI document itself. All we need to do in the Z39.98-AI document is to provide links to one or several such resources.
Here is an example of a MODS record being referenced from the head of a Z39.98-AI document:
Example 5.1 - Referencing an external metadata record: MODS
<head>
…
<meta rel="z3998:meta-record" resource="daisy-z2011-exemplar-01-mods.xml">
<meta property="z3998:meta-record-type" about="daisy-z2011-exemplar-01-mods.xml" content="z3998:mods" />
<meta property="z3998:meta-record-version" about="daisy-z2011-exemplar-01-mods.xml" content="3.3" />
</meta>
…
</head>
The link is labelled with information about the type (and, optionally, version) of the record.
The referenced resource in its turn, is an XML document using the MODS grammar:
Example 5.2 - External metadata record: MODS
<mods xmlns="http://www.loc.gov/mods/v3" version="3.3">
<titleInfo>
<title>Elements of Contract Law: The Sanity Clause</title>
</titleInfo>
<identifier type="isbn13">978-1-56619-909-4</identifier>
<identifier type="isbn10">1-56619-909-3</identifier>
<identifier type="uid">ca-otnlb-0000-0000-0001</identifier>
<name>
<namePart>Otis B. Driftwood</namePart>
<role>
<roleTerm type="text">author</roleTerm>
</role>
</name>
<name>
<namePart>Mrs. Claypool</namePart>
<role>
<roleTerm type="text">editor</roleTerm>
</role>
</name>
<originInfo>
<publisher>DAISY Consortium</publisher>
<place>
<placeTerm>Zurich, Switzerland</placeTerm>
</place>
<dateCreated>2010-01-31</dateCreated>
</originInfo>
<relatedItem type="original">
<originInfo>
<publisher>Book Publisher Ltd.</publisher>
<place>
<placeTerm>New York, NY</placeTerm>
</place>
<dateIssued>2005-03-30</dateIssued>
</originInfo>
</relatedItem>
</mods>
Z39.98-AI is extensible with regards to which types of metadata expression languages can be used in the referenced resources. Note how the meta-record-type meta element in the first example above contains the attribute content="z3998:mods" — this is in fact a reference to the Z39.98-2012 Instance Metadata Vocabulary, which contains a listing of well known metadata expression languages. You can use any of the languages that are available in this listing. And, as metadata expression languages evolve, this listing will be expanded.
In order to enhance interoperability and to take advantage of the different strengths of different metadata expression languages, a single Z39.98-AI document can reference several metadata records. As an example, a document could reference two MODS records, one of them MODS version 3.3 and the other version 4.0, and at the same time reference, say, an ONIX-based record.
5.2 Making the document itself the metadata resource
As an alternative to the external metadata record approach as outlined above, it remains possible to provide a complete metadata record inside the Z39.98-AI document itself. When doing so, you must still provide the meta-record and meta-record-type meta items in the document head to clearly signal that in this instance, the document is its own metadata resource. (See the example below for how this is done.)
All internal metadata expressions are done using RDFa attributes. These can be provided on meta elements in the document head, and/or on various elements in the document body.
The following example shows a document that provides DCMI metadata using the property attribute on h and name elements inside frontmatter:
Example 5.3 - Internal metadata record: RDFa
<document xmlns="http://www.daisy.org/ns/z3998/authoring/" xml:lang="en-GB">
<head>
…
<meta rel="z3998:rdfa-context" resource="http://www.daisy.org/z3998/2012/vocab/context/default/"/>
…
<meta rel="z3998:meta-record" resource=".">
<meta property="z3998:meta-record-type" about="." content="z3998:dcterms-rdfa" />
</meta>
…
</head>
<body>
<frontmatter>
<section role="titlepage">
<h property="dcterms:title">
On the Origin of Species by Means of Natural Selection or the
Preservation of Favoured races in the struggle for life.</h>
…
</section>
…
</frontmatter>
</body>
</document>
Note how, in the head, the metadata resource is identified as ".", a single period. This is standard abbreviated way to refer to the current document URI. In other words, the single period is what says that this document is its own metadata resource.
