Web Services Composition and Geographic Information - Geographical Information Systems: Trends and Technologies - page 132

specifi c Web service resource. In particular, a single Web service can expose
a single data layer ( multiple services method ), alternatively, a Web service can
expose a function for each single OGC service data layer ( facade service )
(Amirian et al. 2010). Finally, for the metadata delivery, three possible
solutions are analysed, namely GetCapabilities function, WSDL extension,
and Metadata exchange. In the fi rst approach, each Web service provides
a GetCapabilities function and a client has to parse the returned values. In
the second approach, all relevant metadata of an OGC service are put in
the extensible part of a WSDL document. The third approach, instead, uses
the W3C WS-Metadata-Exchange specifi cation (Ballinger et al. 2008), that
describes a standard format to encapsulate metadata. The main advantage
of the third solution is that the usage of a standard and documented way
for delivering service metadata drastically reduces the need of developing
customized solutions for metadata retrieval.
In Sancho-Jiménez et al. (2008), the integration of OGC and W3C
services is addressed from another point of view. A method to automatically
retrieve the SOAP interfaces and the WSDL metadata starting from the
mandatory operations (GetCapabilities, Describe Process, and Execute) of
any WPS is proposed. In order to provide these interfaces, the underlying
idea is the creation of an intermediary proxy which is made up of two
sub-modules. The former generates the WSDL metadata used to describe
the WPS interface, the latter adapts a SOAP message in a request suitable
for the WPS interface. As the proposed solution is an automatic derivation
method, in order to generate the WSDL document, a request to the proxy
must contain the URL of the WPS. Through this URL, the proxy uses the WPS
public interface to retrieve all the information needed for the generation
of the WSDL document. Moreover, the proxy offers the possibility to get
both one document containing all the operations offered by the WPS, and
a single document for each of them. Each generated WSDL document will
include both the GetCapabilities and the DescribeProcess specifi cation along
with an Execute method for each operation offered by the particular WPS.
In addition, in order to accurately defi ne the parameters of the Execute
operation, a parsing of the DescribeProcess response is performed. Finally,
on receiving a SOAP request, the proxy fi rst parses the message, gets the
WPS URL and then generates the request and invokes the WPS public
interface.
The INSPIRE Directive
Another important example of diffi culties met when combining the two
standards in a heterogeneous environment handling large amounts of data
can be found in the extensive documentation provided by the Infrastructure