= Metadata Record Sibling Relationships =

|| '''Date''' || 2012-09-20 ||
|| '''Contact(s)''' || Simon Pigot ||
|| '''Last edited''' || 2012-09-20 ||
|| '''Status''' || complete, being discussed ||
|| '''Assigned to release''' || 2.9.0 ||
|| '''Resources''' || Available ||
|| '''Ticket #''' || #XYZ ||

== Overview ==

ISO Metadata records can be related to one another in different ways. The mechanisms for handling these relationships are most often part of the standard in the form of specific elements eg. parent-child relationships are handled through the parentIdentifier element and the datasets that a service delivers are handled through the operatesOn element. !GeoNetwork:
 * can index these relationships to support search
 * has services for retrieving a specific set of related records or the entire collection of related records
This proposal adds sibling relationships between metadata records to !GeoNetwork. The elements in the ISO standard that support sibling relationships are the aggregateInformation element. Sibling relationships types can be specified using an extendible codelist. Sibling records would be displayed under the relationship type. An example of how sibling relations are displayed in the classic interface and the new ExtJS interface is shown below.

[[Image(ClassicSiblingRelationships.png)]]
[[Image(NewSiblingRelationships.png)]]

=== Proposal Type ===
 * '''Type''': GUI Change, Core Change
 * '''App''': !GeoNetwork
 * '''Module''': Lucene Index, ExtJS Experimental Interface, Classic Interface, Services for metadata record relations

=== Links ===
 * '''Documents''': 
 * '''Email discussions''':
 * '''Other wiki discussions''':

=== Voting History ===
 * Vote to be proposed by Simon Pigot, result was +/-n (m non-voting members).

----

== Proposal == 

Aggregate Information in an ISO record that has a related sibling record uses the aggregateInformation element. This looks something like the following:

{{{
    <gmd:aggregateInformation>
        <gmd:MD_AggregateInformation>
            <gmd:aggregateDataSetIdentifier>
                <gmd:MD_Identifier>
                    <!-- optional gmd:authority here: could have details of a register describing the some details of the sibling record -->
                    <!-- code is UUID/urn of the sibling record, could be a gmx:Anchor -->
                    <gmd:code>
                        <gco:CharacterString>urn:marine.csiro.au:project:1532</gco:CharacterString>
                    </gmd:code>
                </gmd:MD_Identifier>
            </gmd:aggregateDataSetIdentifier>
            <gmd:associationType>
                <gmd:DS_AssociationTypeCode codeList="http://...#DS_AssociationTypeCode" 
                                            codeListValue="crossReference">crossReference</gmd:DS_AssociationTypeCode>
            </gmd:associationType>
            <!-- initiative type describes the type of sibling relationship - in this case the code is a project 
                 related to the record that contains this aggregateInformation -->
            <gmd:initiativeType>
                <gmd:DS_InitiativeTypeCode codeList="http://...#DS_InitiativeTypeCode" 
                                           codeListValue="project">project</gmd:DS_InitiativeTypeCode>
            </gmd:initiativeType>
        </gmd:MD_AggregateInformation>
    </gmd:aggregateInformation>
}}}

The UUID of the related record is held in an MD_Identifier element, the associationType is set to crossReference (which seems the most appropriate association type code) and the initiativeType is set to the type of sibling relationship (in this example 'project').

To retrieve and display related records from the aggregateInformation block, we extend the process that is used for parent-child and other relationships:
 * in the java code underlying the !GetRelated guiservice. A simple XPath extraction for all aggregateInformation elements that have an aggregateDataSetIdentifier with a code, an associationType with value set to crossReference and an initiativeType is used to assemble the list of codes (UUIDs/URNs). Sibling metadata records are extracted from the database and attached to the XML output of the !GetRelated guiservice.
 * add processing of the !GetRelated output in relations.xsl which is used in the xml.relation service - returns a simple/brief view of the related records.
 * add processing of related sibling records from guiservice to iso19139/present/metadata-iso19139-utils.xsl - this XSLT generates the classic presentation of related records - see below.
 * add processing of related sibling records from xml.relations to the ExtJS !MetadataRelationStore.js and the ExtJS user interface.  

=== Backwards Compatibility Issues ===
None known.

=== New libraries added ===
None required.

== Risks ==
As is the case with many features of the ISO standard, best practice for the use of the aggregateInformation element is not defined. There is a risk that they way in which we are using this element will not suit all users. However one way of developing best practice is to attempt to use the element in different ways and accumulate experience which we hope will not be too bitter :-)

 
== Participants ==
 * Simon Pigot