Geospatial data models are the heart of geographic information systems, and describe how the data are represented and accessed. Data models need to be precise, and must explicitly define the data elements and the relationships between them for a specific domain. Data models need to allow for data interchange, and include the vocabularies and ontologies that provide meaning to the data.
Geospatial data models support GML schemas in Web Feature Services by developing data mappings, ontologies, and vocabularies. Schemas and ontologies establish common vocabularies for data sharing. GML dictionaries provide controlled vocabularies, or enumerated types, from which to select allowed values for the associated GML properties. Such enumerated types may be defined by external authorities.