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4.1 eXtensible Markup Language (XML)

The recommended long-term record format is expressed using XML 1.0 (eXtensible Markup Language). XML is a text-based markup language. XML specifications are easily extensible (unlike HTML) and are relatively simple. The XML standard is defined by the W3C.

A well formed XML document is a valid document conforming to the syntax defined in the XML specification. A well formed document does not necessarily conform to a Document Type Definition (DTD). A valid XML document conforms to a Document Type Definition (DTD) and the validity constraints in the XML standard.

A VEO must be well formed and valid. The VERS DTD is referenced by the ExternalId of the Document Type Definition. The reference may be the URL of the official VERS DTD (currently http://www.prov.vic.gov.au/vers/published/vers.dtd) as in the following XML fragment:

<!DOCTYPE vers:VERSEncapsulatedObject SYSTEM "http://www.prov.vic.gov.au/vers/published/vers.dtd">

Including this URL in the ExternalId of a VEO will mean that a VERS implementation that uses a validating XML parser will attempt to access this site each time a VEO is accessed, making access very slow. As an alternative, the ExternalId reference may be to a local copy of the VERS DTD, as in the following XML fragment:

<!DOCTYPE vers:VERSEncapsulatedObject SYSTEM "vers.dtd">

If the standard VEO defined in this specification has been extended, the definitions of the extensions must be included in the XML document type declaration markupdecl. Since it must always be possible to validate VEOs, any extensions must be included in the VEOs. Note that the XML standard specifies that these definitions are processed first and consequently override the standard DTD definitions. For example, the following XML declaration adds two attributes to the VERS Standard:

<!DOCTYPE vers:VERSEncapsulatedObject SYSTEM "vers.dtd"
   [ <!ATTLIST vers:Signature dt:dt CDATA #IMPLIED>
<!ATTLIST vers:Certificate dt:dt CDATA #IMPLIED> ]>

VEOs extensively use two namespace: naa and vers.

• The naa namespace is used for elements defined in the NAA Recordkeeping Metadata Standard.
• The vers namespace is used for elements defined by VERS.

The URLs associated with each namespace are treated as simple names by the Namespace standard [Namespace]. According to the standard, the URLs do not need to point to a valid file and do not need to point to an XML schema. In practice, both URLs currently (December 2002) point to human-readable Web pages describing the respective metadata schemas.

An example declaration of these namespaces is:

<vers:VERSEncapsulatedObject
   xmlns:vers="http://www.prov.vic.gov.au/gservice/standard/pros99007.htm"
xmlns:naa="http://www.naa.gov.au/recordkeeping/control/rkms/contents.html">

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