A document type definition for formal metadata
The
metadata compiler I have developed can produce output in Standard
Generalized Markup Language (SGML), a structured system for making
complex textual documents interpretable by computer software. In order to
use the SGML output of the compiler, however, you need an SGML
parser or software that includes one and a document type
definition (DTD) that instructs the parser about the document at hand.
The DTD is essentially a reexpression in SGML of the syntactical rules
given in the FGDC Content Standards for Digital Geospatial Metadata.
NOTE that the use of SGML as an exchange format for formal metadata is
a subject of current study, and some aspects of this work may change
as the National Geospatial Data Clearinghouse develops.
The current version of the DTD has the
following characteristics
- It uses the 8-character tags that are
produced by mp by default. Using tags that are no longer than 8
characters allows the SGML parser to use the Reference Concrete Syntax,
the default SGML declaration.
- It includes entity references for extended characters in the ISO
8859-1 code set. This provides a formal mechanism for encoding European
letters and some symbols such as the degree symbol.
- It has a single placeholder for extensions as a child of
Metadata. This is not particularly satisfactory, and (with help
from others) I am studying ways of adding flexibility to the DTD to allow
extensions to be put in more places.
- It uses PCDATA for scalar (plain-text) values. This allows
you to put symbols and European letters into the text (coded as per ISO
8859-1), representing them in your SGML as the entities referenced by the
DTD.
The DTD is a work in progress. Further progress awaits more widespread
use of SGML to carry metadata, and better tools for handling such SGML
documents. Please contact Doug Nebert
or Peter Schweitzer if you
are interested in furthering this work.
This file is <http://geology.usgs.gov/tools/metadata/tools/doc/dtd.html>
Maintained by Peter Schweitzer
Last updated 17-Mar-1999
