Following are authoritative FGDC Content Standard for Digital Geospatial Metadata (CSDGM) XML schema document (XSD) and document type definition (DTD) URLs for FGDC-STD-001-1998. These documents are used to validate a FGDC XML metadata file.

• http://www.fgdc.gov/metadata/fgdc-std-001-1998.dtd - Usage:
  

  <?xml version="1.0" encoding="ISO-8859-1"?>
  <!DOCTYPE metadata SYSTEM "http://www.fgdc.gov/metadata/fgdc-std-001-1998.dtd">

• http://www.fgdc.gov/metadata/fgdc-std-001-1998.xsd - Usage:
  

  <metadata 
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
       xsi:noNamespaceSchemaLocation="http://www.fgdc.gov/metadata/fgdc-std-001-1998.xsd">

There are also annotated and modified FGDC-STD-001-1998 schema available for download:

• FGDC offers an official, annotated versions of the FGDC-STD-001-1998 schema here: http://www.fgdc.gov/dataandservices/metadata. 
  • Last revision:
    

    20030801 (RER) Changed types of "srcused" (2.5.2.2) and "srcprod"
    	 (2.5.2.5) in Section 2 to reference the type
    	 defined for "srccitea" (2.5.1.5) to comply with
    	 XML Schema constraint that key/keyref field
    	 value pairs be of the same type.

• NOAA offers an annotated versions of FGDC-STD-001-1998 as part of their FGDC Remote Sensing Extensions Schema efforts here: http://sourceforge.net/projects/fgdcxml/files/fgdc%20schemas/ 
  • Additional revision:
    

    20040127 (TS) Moved the types defined in base file, excluding
             the 'metadataType' type, into a separate
             file and included it in the base file.

• NOAA also offers a separate and more recent, annotated version of FGDC-STD-001-1998 as part of their NCDDC efforts here: http://www.ncddc.noaa.gov/metadataresource/metadataandxml/view
  
  • Additional revision:
    

    2009XXXX (RER) Added Annotation information to every compound 
    	and element within the standard. Missing Domain values
    	were added to several types, mostly those types that had
    	domain values and free text. Section 4 mapprojp (4.1.2.1.23) 
    	repeatabilitywas edited from 1-6 to 1-unbounded. Section 5 
    	edom (5.1.2.4.1) repeatability was moved to the sequence. 
    	Section 6 had an extra sequence that was removed.