Global Positioning System Reference
In-Depth Information
the authors discuss also the use of the Common Query Language (CQL)
and some non-standard extensions to the Styled Layer Descriptor (SLD).
The former is a formal language to express queries to information retrieval
systems, the latter is an OGC XML Schema useful for describing the
appearance of a map. The described extensions can be used in conjunction
with GeoServer, a Java based server that supports the editing and sharing of
geospatial data on the Web. The previously mentioned 52° North framework
has been used for the orchestration of OGC services. The issues raised by
the authors include the impossibility to run asynchronous operations, the
need to perform some programming tasks for wrapping, in a WPS, all the
statistical processing needed for the generation of a thematic map and
the use of some GeoServer extensions to SLD. As such customizations are
not part of an OGC standard, the portability of the proposed solution is
limited.
The OGC Program for the Interoperability
When compared to W3C services, OGC services represent a totally
different standard. However, the growing popularity of SOAP, WSDL and
WS-BPEL and the awareness of the great advantages that could result from
the possibility of seamlessly combining these two worlds, led the OGC to
set a special working group in order to provide general recommendations
and guidelines for adding WSDL/SOAP support to existing and future
OGC services.
The fi rst result is the awareness that for OGC services there is the need
to defi ne an Interface Defi nition Language that is a language to describe
the interface of a software component, usually in a language independent
way (Schäffer 2008). A possible choice is, of course, the use of the WSDL.
Currently, in OGC services the role to describe the available operations is
carried out by the GetCapabilities function although a complete intersection
with the WSDL specifi cation is not possible. The main difference is that
WSDL focuses mainly on the description of the explicit interface providing
for both the list of available operations and the types of input and output
messages, while the GetCapabilities provides only for the list of all
operations along with meta-information. The proposed solution is that the
GetCapabilities should list a path to a WSDL fi le that describes the OGC
service. A complementary approach is the possibility for an OGC service
to be discovered by a WSDL document and then, additional metadata
could be fetched by using the traditional GetCapabilities operation. Other
important differences outlined in (Schäffer 2008) are the binding type and
the binding time of operations. In W3C services the message payload is
completely defi ned at design time while in the OGC services the type of a
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