Database Reference
In-Depth Information
where the client requests a connection to the data stream directly to the back-
end system. We use this mechanism for allowing the access to real-time data
in an application scenario, detailed in Section 10.4.
10.3.6 OPeNDAP
We conclude this section by giving a brief overview of a framework that also
provides services, mostly in the form of protocols, to manage and access sci-
entific data. While OGC standard components are designed to handle geo-
referenced data, the Open Source Project for Network Data Access Protocol
(OPeNDAP) standards describe the management of multidimensional array
data that are not necessarily georeferenced.
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OPeNDAP includes specifica-
tions for encapsulating structured data, annotating the data with attributes
and adding semantics that describe the data. In addition to the Distributed
Oceanographic Data System (DODS) protocol that allows users to transpar-
ently access distributed data across the Internet in a way similar to the Get-
Coverage operation in the OGC WCS standard, OPeNDAP has protocols for
exchanging metadata. More specifically, the dataset attribute structure (DAS)
is used to store attributes for variables in the dataset. The dataset description
structure (DDS) is a textual description of the variables and their classes that
make up a scientific dataset.
Existing implementations based on OPeNDAP standards provide a con-
venient framework for retrieving multidimensional scientific data using sim-
ple HTTP-GET requests and are widely used by governmental organizations
such as NASA and NOAA to serve satellite, weather, and other Earth sci-
ence data.
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,
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Since there are no coordinate referencing systems involved in
OPeNDAP standards, they are best used for datasets with a common under-
lying coordinate system. However, OPeNDAP services may not be sucient
when datasets with different coordinate systems need to be integrated. In such
cases, OGC-based services are more suitable. OGC standards and OPeNDAP
standards are not necessarily exclusive. By enhancing multi-dimensional ar-
rays data with proper coordinate systems, it is possible to construct coverages
and serve the data using OGC WCS and WMS standards.
10.4 An Example of an Integration and Interoperability
Scenario
The concept of service-based geospatial data integration can be demonstrated
in many environmental monitoring scenarios. In this section, we consider a
particular environmental scenario involving several integration aspects and
describe the features an integration framework should in general provide to
support such kinds of scenarios.
