Resource Types

Resource Types

In the OGC and MMI URL recommendations, the concept of a Resource Type or Object Type appears. This helps characterize the group of terms that is in a given ontology; roughly, it might represent the class for which each term is an instance.

Examples of possible types of objects are presented below. Note that these objects are generally singular in form, because they are often used to name a class of words, so the singular form is more appropriate.

ISO MD_Keywords:

  • Discipline
  • Place
  • Stratum
  • Temporal
  • Theme

OGC Object Types (Reference:

  • axis (coordinate system axis)
  • axisDirection (axis direction code)
  • coordinateOperation
  • crs (coordinate reference system)
  • cs (coordinate system)
  • datum (geodetic datum)
  • dataType
  • derivedCRSType (derived CRS type code)
  • documentType
  • ellipsoid
  • featureType (feature type, as specified in an application schema, per ISO 19109)
  • group (operation parameter group)
  • meaning (parameter meaning)
  • meridian (prime meridian)
  • method (operation method)
  • nil (explanations for missing information)
  • parameter (operation parameter)
  • phenomenon (observable property)
  • pixelInCell (pixel in cell code)
  • rangeMeaning (range meaning code)
  • referenceSystem (value reference system)
  • uom (unit of measure)
  • verticalDatumType (vertical datum type code)

Other Concepts for Object Type

  • keyword
  • parameter
  • units
  • organization
  • platform
  • sensor
  • process
  • missingFlag
  • qualityFlag
  • qcCategory
  • coordinateReference
  • datum
  • protocol
  • metadataStandard
  • featureType and featureName (e.g. in gazetteer, or an entity being observed)
  • speciesTypes and speciesNames (e.g. as used in OBIS)
  • discipline
  • place
  • theme
  • quantity
  • constraint (used to limit scope of other entities)
  • roleOfContact
  • general metadata attribute

Other Discriminators in the resourceType Field

We previously allowed for the possibility that the ontology name may include the authority, as in mmi_platform.owl. For various reasons, it may be necessary to discriminate beyond simply the authority and resource type. In those cases, we recommend two additional options.

The first option is to indicate further details or descriptive information about the ontology, or even to use an index number. So varieties of the place.owl ontology might include place_marine, place_geographic, or place_governmental; or could simply be labelled place_01.owl.

An additional option is to reflect the nature of the ontology, particularly whether or not it is a mapping. A placenames ontology file that actually serves to map vocabularies would be called place_map.owl or place_maine_owl.

While it is not essential that the ontology topic, ontology file name, and top class in the ontology all match, this can make the file easier to use and understand. It is therefore recommended to follow this approach when it is straightforward.

Resource Types and Top Ontologies

Note: This section is still under consideration, and has not been carefully reviewed or implemented in MMI services.

The previous objects, as well as others, could be represented as classes in a top ontology. For example an will represent all the parameters in the marine world known by MMI.

Each ontology submitted or stored at MMI, should have at least on concept from that ontology match with an MMI object. For example the CF standard variables are all instances of a class that is
This class can be declared as SubClass of

Each ontology authority should have a central top ontology with all the resource types that it wants to make public. Each of these resource types may eventually correspond to a specific ontology, and the name of the ontology could then share the resource type term. (While this is by no means a requirement, it creates a relatively transparent practice for identifying the sets of terms offered by the authority, and describing each set of terms.)

The top ontology only declares the top concepts, but should not import any concrete ontology. A concrete ontology (like the CF Standard Variable Names at MMI) should always import the top ontology. Every ontology provider should try to have a top ontology or should reuse an available one.


Ontology is the philosophical study of the nature of being, existence or reality in general, as well as the basic categories of being and their relations. Traditionally listed as a part of the major branch of philosophy known as metaphysics, ontology deals with questions concerning what entities exist or can be said to exist, and how such entities can be grouped, related within a hierarchy, and subdivided according to similarities and differences. While the etymology is Greek, the oldest extant record of the word itself is the Latin form ontologia, which appeared in 1606, in the work Ogdoas Scholastica by Jacob Lorhard and in 1613 in the Lexicon philosophicum by Rudolf Göckel.
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