There is work in progress to define an XML representation for the UK
e-Government Metadata Standard (e-GMS). The specification will probably be
out for consultation  on the UK GovTalk website c. mid-August
(http://www.govtalk.gov.uk); in the meantime, it may be useful for you to
have this extract (below) from the current working draft (0.3), which
describes the design criteria and rationale.

Regards,

Ann W.


Ann M Wrightson MA MBCS
Prif Ymgynghorydd / Principal Consultant
alphaXML Cyf/Ltd
http://www.alphaxml.com
Gwasaneuthau XML: e-Lywodraeth, e-Fasnach, e-Gyhoeddi
XML services to Government and Industry

Representing e-GMS metadata in XML
DRAFT
Extract for DC & DSDL comment 18 Jul. 02

Document version 0.3

1.2 Background
The e-Government Metadata Standard is technology-independent. Amongst  other
representations, e-GMS metadata will certainly occur in XML, for  example,
in XML messages containing metadata, and in XML documents with  embedded
metadata. e-GMS metadata in XML is likely to occur in a number  of different
contexts, including:
* embedded within XML schema documents (prepared according to W3C XML
Schema Recommendation 2001)
* embedded within XML documents fulfilling specific functions, eg public
records, and reports submitted for specific regulatory purposes
* information exchanged using an XML message includes e-GMS metadata  about
something outside the message
* within a dedicated metadata repository
* as a block of descriptive metadata within a wider metadata framework  such
as the Metadata Encoding and Transmission Standard (METS)
* supplementary metadata attached to an existing XML document, eg  metadata
created when a record is selected for long term preservation;  or metadata
pertaining to the role of a pre-existing document within a  set of documents
collected for a Public Inquiry.
1.3 Key design issues for XML representation of e-GMS metadata
This section discusses key design issues, and lists the design criteria  for
the XML representation of e-GMS metadata arising out of the issues.
In the lists of design criteria, "e-GMS-XML" is used as a short form of  "an
XML representation of general-purpose e-GMS metadata"; and "W3C
Schema-validation" for "validation according to W3C XML Schema
Recommendation 2001".
1.3.1 Long life of metadata
e-GMS metadata can be expected to be long-lived, and contribute to the
management, discovery and utilization of electronic resources over a  long
life for the resource (eg >100 years for an e-archive of electronic  public
records). XML is an ISO standard as well as a widely adopted  industry
standard, and a successor to a very similar standard already 25  years old -
and so is very likely to be long-lived. W3C XML Schema,  although a good
choice at present for schema definition within e-GIF, is  less likely to be
long-lived, since there are competing schema languages  for XML (which may
in future gain wider industry acceptance). In  addition, an ISO XML schema
standard is under development, which is  intended to encompass and harmonize
current approaches into a long-lived  stable standard.
Bearing all this in mind, it is advisable for the XML representation of
general-purpose e-GMS metadata to be independent of specific features of
W3C schema-validation, whilst also being compatible with the immediate
e-GIF requirement to validate XML by this means.
XML is likely to be long-lived. However, some public sector documents  have
a very long projected lifetime, and it is unlikely that XML will  remain the
standard of choice for interoperability over all that time.  The nature and
wide adoption of XML makes it unlikely that document  content in XML will
become unusable, since XML viewing applications are  likely to remain
available in the long term. However, the principal  utility of metadata is
in its daily use to support integrated access to  current and past
information resources, so it is quite likely that  metadata in XML will
eventually become functionally obsolete. Because of  this, e-GMS metadata in
XML should be easy to convert to a successor  data format.
Design criteria:
* e-GMS-XML does not depend on specific features of W3C  Schema-validation,
but rather uses XML structures which are likely to be  straightforward to
validate using any future XML schema language
* e-GMS-XML is compatible with the immediate e-GIF requirement to  validate
XML documents and messages using W3C Schema-validation
* e-GMS-XML is likely to be easy to translate into a future successor
format to XML
1.3.2 Compatibility with Dublin Core
The e-GMS metadata standard is based on Dublin Core. Standardized XML
representation of Dublin Core metadata is currently under development in
DCMI. The design criteria and principal scenarios of use for metadata  are
different between DCMI and UK Government; this is already evident in  the
e-GMS itself, where some aspects depart from DCMI principles.  Because of
this, simple adoption of the Dublin Core XML representation  for e-GMS is
unlikely to be appropriate. However, it is highly desirable  that
interoperation between e-GMS metadata and generic Dublin Core  metadata
should be easy to achieve - if that were not so, then the main  intended
benefit of basing e-GMS on Dublin Core would be lost.
The concept of "dumb-down" use of metadata is important for
interoperability between metadata-aware applications with different
capabilities. The key point is that when any metadata processor looks at  a
set of metadata, it should be able to identify and use all the  metadata
elements which it can understand. In particular, refinements  which it does
not understand can be ignored, and the value of an element  refinement used
as if it were the unrefined element.
In general, "dumb-down" is a forgetful yet faithful metadata  translation,
preserving faithfully from a more expressive metadata form  all & only what
a less expressive metadata form can express. In the  context of e-GMS,
"dumb-down" metadata processing is likely to have two  forms: processing
metadata devised according to an e-GMS local metadata  standard as if it
were generic e-GMS metadata; and processing e-GMS  metadata of any kind as
if it were simple Dublin Core.
Design criteria:
* e-GMS-XML can be mapped to the Dublin Core standardized XML
representation in a straightforward manner, for those metadata elements
common to e-GMS and Dublin Core. This provides a proper "dumb-down"
metadata mapping of e-GMS to Dublin Core.
* e-GMS-XML supports "dumb-down" processing of metadata conforming to an
e-GMS local metadata standard as if it were generic e-GMS metadata, in a
uniform and straightforward manner.
1.3.3 Interdependency and more complex constraints on metadata elements
e-GMS metadata has constraints on the optionality and interdependency of
its elements, and some of these constraints are not suitable for direct
validation using W3C Schema-validation. The ISO schema standard under
development is intended to support more of this kind of functionality,  but
it is not yet clear whether this will gain widespread industry  support.
There are also a number of industry standards and initiatives  providing
capabilities in this area. Just as for the ISO standard, the  nature and
depth of industry support for these approaches in the medium  term is
uncertain.
Local metadata standards based on e-GMS are likely to introduce more of
these kinds of constraints, since metadata will be used to represent  data
pertaining to business rules. XML validation is principally  designed to
validate the structure of an XML document, and the data type  of XML element
content. However, these capabilities are often used to  enforce business
rules, and it is widely seen as a virtue that XML  validation should extend
as far as possible in this direction. This  situation makes it difficult to
be precise about a suitable boundary  between XML validation and
supplementary validation for metadata.
Design criteria:
* where e-GMS-XML requires validation over and above validation of the
structure and data type of the XML, this  is simple, and specified in a
technology-independent manner
* where these more complex constraints are supported by widely used XML
technologies, then guidelines and best practice on using these should be
provided
1.3.4 Interoperability between XML metadata technologies
XML metadata is an area where there are a number of standards, and these
standards tend to be complementary rather than competing (though they  may
be competitors in the context of a specific application). The  picture is
made more complex by the fact that these standards come from  different
domains only now converging through the ubiquity of Internet  technology -
for example, there are well-regarded standards with origins  in
librarianship and information science (Dublin Core), artificial
intelligence (DAML/OIL), and electronic publishing (ISO 13250 Topic  Maps),
together with efforts to integrate the metadata domain in its own  right
(ISO 11179, METS), as well as the ongoing work in W3C.
Although it is desirable to have a uniform XML representation of e-GMS
metadata, it is also important to enable Government organizations to  choose
freely between technology solutions based on different industry  standards.
This is particularly important since some Government  organizations have
close ties to specific industry sectors.  An  important first step has been
taken by making the e-GMS standard itself  technology independent.
At one extreme, fine-tuned XML representations of e-GMS metadata could  be
devised for each specific context, using a range of XML metadata
technologies. However, this would lead to a large number of different
"standard" representations, and discourage easy interoperability.  Another
approach would be to define a rigid "one size fits all" XML  representation.
Neither of these is likely to meet the practical  requirements of Government
organizations. The design criteria below are  intended to offer a reasonable
middle way.
Design criteria:
* e-GMS-XML provides datatype definitions for e-GMS metadata element
values. These will be a common resource for all e-GMS XML  representations.
* e-GMS-XML provides a representation designed for use in an e-GIF XML
message containing metadata about something outside the message. This is
the most general form of e-GMS metadata in XML, designed to accommodate  any
(technology independent) e-GMS local metadata standard, and thus  providing
a simple basis for interoperability between any e-GMS  complaint systems.
* e-GMS-XML provides a representation designed to sit within the context  of
an XML document. This could be within the XML data for a publication  (eg a
report), or within another XML context such as a METS descriptive  metadata
section.
* e-GMS-XML provides guidelines and examples for using e-GMS with  selected
XML metadata technologies. The aim of these guidelines is to  support, for
example, easy interoperability in RDF between e-GMS  compliant systems using
RDF. These guidelines are expected to evolve  over time, as specific XML
metadata technologies gain and lose  acceptance in the marketplace.
* e-GMS-XML provides guidelines for designing XML representations of  e-GMS
local metadata standards (it is envisaged that the e-GMS XML  schema local
metadata standard will be updated to conform to these  guidelines in due
course).
2 Requirements for Implementation
The utility of this specification depends on the availability of
standardized value sets and notations to provide commonly understood
meanings for the metadata element values. This requirement is a general  one
for metadata. However, there is also a more precise requirement for  the XML
representation of e-GMS metadata.
The standardized value sets and notations used in e-GMS metadata must  have
concise names suitable for use as XML attributes. These names must  be
persistent, that is, they must be as far as possible guaranteed to  retain
their significance for as long as the metadata is expected to be  retained
(including possible preservation as a public record).
The following are NOT suitable for use as names for value sets and
notations in this context:
* URLs or URIs, unless specifically designed for the purpose and  guaranteed
by a long-lived and trusted authority
* An XML schema namespace name (it is a technology-specific surrogate  for
the notation name).
It is recommended that standardized value sets and notations used in  e-GMS
metadata are administered in a registry designed for long-term  persistence
as a reference for understanding e-GMS metadata. The  persistence and
integrity of this registry is essential for the  accessibility and usability
of Government information in the long term.
3 References
1
e-Government Interoperability Framework (e-GIF) v4
http://www.govtalk.gov.uk/interoperability/egif_document.asp?docnum=534
2
e-Government Metadata Standard v1.0 April 2002
http://www.govtalk.gov.uk/interoperability/metadata_document.asp?docnum= 524
3
e-Government Local Metadata Standard for XML Schemas v1.0 May 2002
GSG paper Q2 2002
4
e-GIF XML Architecture
GSG paper Q1 2002
5
Resource Description Framework (RDF)
http://www.w3.org/RDF/
6
Government Data Standards Catalogue (GDSC), all volumes
http://www.govtalk.gov.uk/interoperability/eservices.asp?order=title
7
Metadata Encoding and Transmission Standard (METS)
http://www.loc.gov/standards/mets/
8
Dublin Core Metadata Initiative work in progress
http://www.ukoln.ac.uk/metadata/dcmi/xmlschema/