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.
GML application schema development is special case of data modeling where a GML application schema is used to express the common vocabulary.
Data modeling includes creating a schema mapping, from a relational schema to an XML schema, and vice versa. Data models are often specified using the OMG Unified Modeling Language (UML). UML is a standardized general-purpose modeling language; a subset of UML diagrams, together with supporting documentation, provides a rich way to describe data structures.
The W3C Resource Description Framework (RDF) is a suite of recommendations that provide a standard model for data interchange on the web. RDF facilitates merging data even if the underlying schemas are different, and it provides specific support to allow schemas to evolve over time without requiring changes in the data consumers. Using RDF helps to ensure that a data model is not locked into a specific version of a schema, which would require updating whenever a new version is released.
An ontology provides a shared vocabulary for a domain or data model, describing the type of objects and/or concepts that exist, and their properties and relationships. The W3C Web Ontology Language (OWL) is designed for use by applications (machines and systems) that process information and data. OWL is a collection of languages for representing knowledge, providing semantic meaning to data, and making it easier for machines to interpret.
INterchange™ Schema Mapper was developed by Galdos for use in defining mappings between schemas, and for creating XSLT transformations from the mapping file.
INdicio™ Web Registry provides a useful way to store, index, and make accessible GML dictionaries and code lists for ontologies and vocabularies.
Galdos was one of the companies in the consortium that developed ontologies for NATO in the Core GIS Data Preparation project.
Additional details on various Galdos projects are available in the Case Studies.
