Encoding URIs in ISO 19139

ISO 19139 is the application of the ISO 19115 Geospatial Metadata Standard. It is being used to describe resources within Catalog Services for the Web (CSW). A resource can be, among others, a layer, an observation, a coverage, or a feature. These could be served respectively as WMS, SOS, WCS, and WFS. Ideally we would like to discover these resources registered in a catalog by using controlled vocabularies and relation that can exists among terms. For example searching for recreation we should be able to get a web services that provide public beaches data.

Control Vocabularies exist, but not all of them are Web accessible. If communities make these controlled vocabularies available in the Web, persistence and integration of information will be much easier. For this to happen, we need to:

  • Publish the controlled vocabularies in machine readable format in the Web. And, use the Web artifacts such as Uniform Resource Identifiers (URIs) to identify both the terms and the vocabulary. Ontologies (OWL, SKOS, and RDF) are the a mechanism to publish these vocabularies in the Web using URIs as identifiers.
  • Tag the metadata (using ISO 19139) about the registered resources with concepts available from these vocabularies published in the Web. ISO 19139 provides and element  <gco:CharacterString> that place the string value of the concept. However, there are substitutions, e.g. <gmx:Anchor>  that can be use to better encode the URIs

Two approaches are shown bellow. One without URIs and the second one with URIs:

1) If we are not using URIs it is fine to use this approach. For example:

<gmd:descriptiveKeywords>

    <gmd:MD_Keywords>


       
<gmd:keyword>

           
<gco:CharacterString>String of a local concept in a theaurus</gco:CharacterString>

       
</gmd:keyword>

       
<gmd:thesaurusName>

           
<gmd:CI_Citation>

               
<gmd:title/>

               
<gmd:date/>

               
<gmd:identifier>

                   
<gmd:MD_Identifier>

                       
<gmd:code>

                           
<gco:CharacterString>String of the thesaurus name</gco:CharacterString>

                       
</gmd:code>

                   
</gmd:MD_Identifier>

               
</gmd:identifier>

           
</gmd:CI_Citation>

       
</gmd:thesaurusName>

   
</gmd:MD_Keywords>

</gmd:descriptiveKeywords>

 

2) If we are using Ontologies a term and the controlled vocabulary are represented via a URI, and the <gmx:Anchoris use instead of <gco:CharacterString>.

<gmd:descriptiveKeywords>

    <gmd:MD_Keywords>

        <gmd:keyword>

            <!-- use gmx:Anchor which provides xlink capabilities that will better provided tagging metadata with URIs from ontologies. This replaces <gco:CharacterString> -->

            <gmx:Anchor xlink:href="http://mmisw.org/ont/agu/indexterm/_2704">

                Auroral phenomena

            </gmx:Anchor>

        </gmd:keyword>

        <gmd:thesaurusName>

            <gmd:CI_Citation>

                <gmd:title/>

                <gmd:date/>

                <gmd:identifier>

                    <gmd:MD_Identifier>

                        <gmd:code>

                            <gmx:Anchor xlink:href="http://mmisw.org/ont/agu/indexterm">

                                AGU Index Term

                            </gmx:Anchor>

                        </gmd:code>

                    </gmd:MD_Identifier>

                </gmd:identifier>

            </gmd:CI_Citation>

        </gmd:thesaurusName>

    </gmd:MD_Keywords>

</gmd:descriptiveKeywords>