Microsoft Word 16 ok6408. doc

2. 
ONTOLOGY-BASED GEO-OBJECT CATALOGS
An Ontology-based Geo-Object Catalog (OGOC) acts as a focal point for 
a federation of independent geo-object sources, providing consolidation 
services for the geo-objects represented in several sources, as well as access 
services to query objects and metadata.
To accomplish this task, an OGOC stores a reference ontology and 
ontologies representing the conceptual schemas of the geo-object sources. 
The reference ontology may include a set of reference instances.
1
OpenGIS Consortium: 
http://www.opengis.org

---

238 
A reference instance represents, in a consolidated way, a collection of 
geo-objects, stored in distinct sources, that refer to the same real-world 
object. Each reference instance belongs to a class in the reference ontology 
and carries attributes that identify the equivalent geo-object in each source. 
In this way, the catalog provides means to determine equivalent classes and 
equivalent geo-objects from distinct sources. 
Figure 1 schematically shows the use of the reference ontology (R
O
) and 
of the reference instances (I
R
) to map, respectively, the local ontologies and 
the local geo-objects from two federated geo-object sources. 
The mapping between the local ontologies and the reference ontology 
will be based on generic relationships, such as subClassOf and sameClassAs, 
and on relationships that depend on the application domain. 
Figure 1 - Geo-objects and ontologies mappings. 
An OGOC may be used to mediate access to the geo-object sources, 
acting as the pivot of a federation of objects sources. To be part of the 
federation, each source must follow the participation protocol: (1) register 
the source in the OGOC, informing the source’s conceptual schema (an 
ontology, in the OGOC ontology description language); (3) map the source 
ontology to the reference ontology; and (4) provide the set of geo-objects, 
with its basic attributes, that the source wishes to share, in the context of the 
federation. 
To summarize, an OGOC: 
• covers a specific application domain, where interoperability among geo-
object sources is needed; 
• provides a reference ontology for the application domain, with classes, 
basic properties and relationships definitions; 
Reference 
Ontology