240 Figure 2 - OGOC generic architecture. • GetObject: provides queries to sets of objects, defined using filters,
based on the properties of the geo-object types. A special parameter
may be added to enable the use of an ontology-driven cooperative
behaviour strategy that helps the requester achieve its goals, by
allowing the system to apply transformations to queries and answers. • Inference Module: provides inference services that allow more
sophisticated queries to be formulated against the catalog geo-objects and
metadata.
• Reference Ontology: describes, in the federation application domain,
classes, basic properties and equivalence relationships that provide an
integrated vision of the ontologies of the federated geo-object sources.
• Ontology Repository: stores and manages ontologies that describe
federated geo-object sources and OGOC reference ontology.
3.2 A Framework for Customized Catalogs The generic architecture described in the previous section suggests the
definition of a framework (Fayad and Schmidt, 1999) that generates
customized catalogs by instantiation.
The frozen-spots and hot-spots of the framework are defined to
accommodate changeable characteristics of the application domain.
The proposed framework has the following frozen-spots:
Ontologies
Manipulation
Module
Objects
Manipulation
Module
Interface Inference
Module
Reference Ontology (RO) I R R O DB 1 DB 2 Ontologies Repository
Objects Mappings Mappings with RO Ontology O 2 Objects
