data; and returns data with its original semantics instead of pictures which may be interpreted, extrapolated, etc. – and not just portrayed.
Unlike WFS, which returns discrete geospatial features, the Web Coverage Service returns coverages representing space-varying phenomena that relate a spatio-temporal
domain to a possibly multidimensional range of properties.
A description of WCS and JPIP are provided in Section 5.5.3
.
5.3.5 Catalog
• Data Catalogs. The regional data centers will each automatically maintain catalogs of the data and information they contain. When data searches are conducted, the queries
will be responded to by data center catalog services and provide the requesters with all relevant information in response to the query. This information will include content
parameters such as source and age of the data as well as management data such as when originally stored, last verified and last retrieved. Content metadata will convey the
confidence level of data in terms of reliability, currency and accuracy.
A catalog is a database of information about geospatial resources data, services, and related information objects available to a group or community of users. A catalog
typically stores descriptive information about the resource being described, and does not store the information resource itself. The interfaces on catalogs enable services that are
collectively referred to as Catalog Services in OGC. We use the term “catalog” or “catalog services” to describe the set of service interfaces that support organization,
discovery, and access of geospatial information. Catalog services help users or application software to find information that exists anywhere in a distributed computing
environment. These resources function in this environment through interfaces that implement OpenGIS Specifications. Interaction with geospatial data collections via their
metadata is done via catalog services. Catalog services are required to support the discovery and binding to registered information resources within an information
community.
5.3.5.1 Catalog components
The OpenGIS Catalog Service Interface Specification enables diverse but conformant applications to perform discovery, browse and query operations against distributed and
potentially heterogeneous catalog servers. The Catalog Interface specification uses metadata and spatial location to identify and select data sources of interest, and provides
for interoperability in catalog update, maintenance, and other librarian functions.
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Copyright © 2007 Open Geospatial Consortium, Inc. All Rights Reserved.
The General Catalog Interface Model provides a set of abstract service interfaces that support the discovery, access, maintenance and organization of catalogs of geospatial
information and related resources. The interfaces specified are intended to allow users or application software to find information that exists in multiple distributed computing
environments, including the World Wide Web WWW environment. All behavior requiring sessions is expressed by a dynamic model of conversation state and state
transitions. The model expresses the states and messages that trigger the changes in state.
An Application Profile is predicated on the existence of one protocol binding in the base specification. In the case of the Catalog Services Specification, a profile could reference
CORBA, Z39.50, or HTTP protocol bindings. In most, but not all, protocol bindings, there may be restrictions or refinements on implementation of the General Model agreed
within an implementation community.
Figure 7 - Catalog Reference Model Architecture, shows the Reference Architecture assumed for development of the OGC Catalog Interface. The architecture is a multi-tier
arrangement of clients and servers. To provide a context, the architecture shows more than just catalog interfaces. The bold lines illustrate the scope of OGC Catalog and
Features interfaces.
The Application Client shown in Figure 7 - Catalog Reference Model Architecture interfaces with the Catalog Service using the OGC Catalog Interface. The Catalog
Service may draw on one of three sources to respond to the Catalog Service request: a Metadata Repository local to the Catalog Service, a Resource service, or another Catalog
Service. The interface to the local Metadata Repository is internal to the Catalog Service. The interface to the Resource service can be a private or OGC Interface. The interface
between Catalog Services is the OGC Catalog Interface. In this case, a Catalog Service is acting as both a client and server. Data returned from an OGC Catalog Service query is
processed by the requesting Catalog Service to return the data appropriate to the original Catalog request.
describes OGC Interfaces
Applicatio Application
Applicatio Server
Catalog Service
Metadata local
Metadata Data
Data OGC Catalog
Interface
Private Interfaces
Repository Client
Federated Search
Figure 7 - Catalog Reference Model Architecture
Resources in a catalog are discovered using a filter. Queries can be temporally constrained using the standard scalar operators found in the Filter specification
PropertyIsBetween, PropertyIsEqualTo, etc .... However, the Filter specification does
Copyright © 2007 Open Geospatial Consortium, Inc. All Rights Reserved.
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