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Copyright © 2012 Open Geospatial Consortium.
8.1.1 Standard Names
The standard names used in the CF conventions are a special case of a NetCDF standard term. They are designed to provide an unambiguous reference to the property that a
variable measures. The CF standard name table provides a small amount of semantic information: canonical units, descriptive text, aliases and mappings onto a small number
of similar codes. However, standard names are generally used in software simply to ensure that like is compared with like.
Where possible, the variables in the document should have a standard name that reflects the property of the observation. If the standard name is taken from a specific vocabulary,
the vocabulary should be recorded in the observation metadata and specified in the NetCDF global attributes see Section 10.2. Where standard names can be mapped onto
URIs, a dictionary should be included see Sections 8.1.4 and 10.4.1
Standard names can be derived from either a repository of standard names, such as the CF name table, by tokenizing a property URI see Section 8.1.2 or by using data
available from RDF see Section 8.1.3.
8.1.2 URI Tokenization
Enumerations for URIs or terms from a standardized vocabulary can be constructed by tokenizing either the xlink:title value from the link to the URI, the fragment of the URI,
the last path segment of the URI or the label or id of an AbstractSWEType. Tokenizing replaces whitespace and other non-alphanumeric characters with underscores and
converts camelcase to lower case separated with underscores. For example:
Table 2 URI Tokenization Examples
Term Tokenized
http:www.opengis.netdeftimeseriesTypeWaterML2.0MinSucc min_succ
Water Temperature water_temperature
http:purl.oclc.orgNETssnxcfcf-propertyrainfall_amount rainfall_amount
Tokenized URIs can be associated with the actual URI by use of a dictionary – see
Section 8.1.4.
8.1.3 Use of RDF
In many cases, URIs can be resolved to semantic descriptions of the URI, usually in the form of RDF. In such cases, values derived from the RDF can be used to provide
standard name tokens and other property-specific information.
Copyright © 2012 Open Geospatial Consortium.
17 For example, the following RDF description of rainfall is extended from the CF
properties ontology
3
, developed by the Semantic Sensor Networks working group. The rdfs:label property can be used to derive a suitable long name and the cf:standardName
can be used for the CF standard name.
dim:SurfaceDensity rdf:about=http:purl.oclc.orgNETssnxcfcf- propertyrainfall_amount
rdfs:labelRainfall Amountrdfs:label rdfs:commentAmount means mass per unit area.rdfs:comment
dc:sourceClimate and Forecast CFdc:source cf:standardNamerainfall_amountcf:standardName
qu:generalQuantityKind dim:SurfaceDensity
rdf:about=http:purl.oclc.orgNETssnxququantitysurfaceDensity qu:generalQuantityKind
ssn:isPropertyOf cf-feature:Precipitation rdf:about=http:purl.oclc.orgNETssnxcfcf-
featurerainfall ssn:isPropertyOf
qu:propertyType qu:PropertyKind rdf:about=http:purl.oclc.orgNETssnxququantityscalar
qu:propertyType dim:SurfaceDensity
8.1.4 Dictionaries and Vocabularies