80 Figure 12. Proposed semantic mapping between ISO metadata record to semantic
metadata in a CSW server
6.4.2.2 An extended OGC query for semantic data search
The OGC CSW specification defines a standard but extensible interface for discovering and querying metadata about geospatial resources over HTTP. Through the OGC CSW
interface, users define their data search criteria using OGC Filter Encoding OGC 09- 026r1. To enable semantic search for discovering semantically related dataset, the
standard OGC Filter Encoding and its Extensions package can be enhanced by introducing a new search operator “DataIsRelated”. This new operator can take two input
parameters. The first parameter is either an identifier of a data record or a concept term; the second specifies the data search context. This new operation will return a list of
metadata records relevant to the given data or the given concept term under a specified search context. This new operator can be combined with other operators, such as spatial
relations and value comparisons, predefined in the OGC Filter Encoding specification to achieve more complicated search capabilities. Figure 13 shows an example OGC CSW
query
that leverages the new “DataIsRelated” operator to find data records relevant to a data object identified by identified id93872 in terms of lineage and whose content is
related to “hydrology”.
?xml version=1.0 encoding=ISO-8859-1?
GetRecords service=CSW version=2.0.2 maxRecords=500 startPosition=1 resultType=results outputFormat=applicationxml
outputSchema=http:www.opengis.netcatcsw2.0.2 xmlns=http:www.opengis.netcatcsw2.0.2
81
xmlns:ogc=http:www.opengis.netogc xmlns:cnd=http:daac.ornl.govcatalogconnected-data
xmlns:xsi=http:www.w3.org2001XMLSchema-instance xsi:schemaLocation=http:www.opengis.netcatcsw2.0.2
......csw2.0.2CSW-discovery.xsd Query typeNames=Record
ElementSetNamebriefElementSetName Constraint version=1.1.0
ogc:Filter ogc:And
cnd:DataIsRelated cnd:RelationContextContentcnd:RelationContext
cnd:Concepthydrologycnd:Concept cnd:DataIsRelated
cnd:DataIsRelated cnd:RelationContextLineagecnd:RelationContext
cnd:DataObjectid93872cnd:DataObject cnd:DataIsRelated
ogc:And ogc:Filter
Constraint Query
GetRecords
Figure 13. Example OGC CSW Query for semantic data search aspatial Figure 14 demonstrates another enhanced CSW query that combines semantic search
based on the semantic association definition and the spatial filter. This query tries to identify all hydrology related datasets. These datasets should cover a requested spatial
area, defined by bounding box “3.19 50.67; 7.26 53.59”.
?xml version=1.0 encoding=ISO-8859-1? GetRecords service=CSW version=2.0.2 maxRecords=500
startPosition=1 resultType=results outputFormat=applicationxml outputSchema=http:www.opengis.netcatcsw2.0.2
xmlns=http:www.opengis.netcatcsw2.0.2 xmlns:ogc=http:www.opengis.netogc
xmlns:cnd=http:daac.ornl.govcatalogconnected-data xmlns:xsi=http:www.w3.org2001XMLSchema-instance
xsi:schemaLocation=http:www.opengis.netcatcsw2.0.2 ......csw2.0.2CSW-discovery.xsd
Query typeNames=Record ElementSetNamebriefElementSetName
Constraint version=1.1.0 ogc:Filter
ogc:And
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