Copyright © 2006 Open Geospatial Consortium – All rights reserved
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Intergrated Client CS-W
GetRecords Service_Query Service Endpoints
GetRecords EO_Query Extrinsic Objects
Figure 18 Catalog Retrieval
In this example an integrated client is provided with the URLs of the Catalog Service endpoints. Based on user input, a query is constructed with which a GetRecords request
is made to find Extrinsic Objects based on the object type FeatureType, WMS_Layer, ObservationOffering. The response will include the objects identified along with
metadata about the object including an id for each object. Another GetRecords request can then be constructed to build a Service request to identify the service endpoints for
each object. With this information the user has the information needed to bind to the appropriate data.
13.2 Issues and Tradeoffs with Catalog Service for the Web Communication
This section presents a summary of interoperability issues discovered while working with the CubeWerx and IONIC ebRIM 2.5 catalogs.
13.2.1 Locating Extrinsic Objects by Object Type
The ebRIM model provides an attribute named objectType on the ExtrinsicObject element. ebRIM 2.5 restricts the value of this attribute to a URN of type UUID. This
UUID is meaningful only to a particular catalog instance and its meaning must be derived by lookup from the ebRIM classification structure. This obfuscation makes it awkward,
we believe, to simply find extrinsic objects by type.
The participants in the OWS-3 Common Architecture thread agreed that for the purposes of the initiative we would deviate from the ebRIM 2.5 profile and use simple English
names for the value of objectType. For the purpose of this testbed, the following values were recognized:
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Copyright © 2006 Open Geospatial Consortium – All rights reserved
Service Object Type
WMS WMS_Layer
WFS FeatureType
SOS ObservationOffering
GVS VideoFeed
A recent version of the ebRIM profile document provides more flexibility for objectType, in that it may take on a URN of the form:
urn:ogc:specification:csw-ebrim:objectType:Dataset: Here are representative URNs proposed by CubeWerx that may be considered in future
ebRIM catalog implementations: Service
Object Type WMS
urn:ogc:specification:csw-ebrim:objectType:Dataset:WMS_Layer WFS
urn:ogc:specification:csw-ebrim:objectType:Dataset:WFS_Feature
13.2.2 Association Types
A key concept of the ebRIM catalog model is the Association. Clients make use of an association to relate an extrinsic object to a service. To promote catalog interoperability,
we feel it is important to standardize a core set of association types. Here are interoperability issues we encountered in working with associations:
operatesOn vs. OperatesOn: We noted variations in the capitalization of the association name.
OperatesOn vs. HasForContents: Does an SOS OperatesOn an ObservationOffering or does it HasForContents same?
13.2.3 Case of Keywords
We believe it should be possible for a catalog to ignore case in user-specified keywords. More generally, this means allowing for the possibility of case-insensitive treatment of
the value of Literal elements in the OGC Filter expression.
13.2.4 Predicate on Spatially Restricted Searches
