Global Positioning System Reference
In-Depth Information
al. 2007). The retrieval of information about the status of the process can
be performed in two different ways: the pull and the push mechanisms. In
the former the client carries out a periodic check, in the latter the service
provider sends a notifi cation about the status of the process. According
to the authors the push mechanism is more convenient to alert humans
(e.g., by email or SMS) while the pull mechanism is more suitable for
the machine-to-machine communication. The pull mechanism is directly
supported by the WPS standard. In such a mechanism the response of a
WPS to the Execute request is an XML fi le containing a link pointing to a
constantly updated Execute response document. During the processing
this document contains the status of the operation, when the processing is
fi nished the provided URL contains the link to the fi nal result. However,
the asynchronous approach raises other research questions, such as what
happens when an asynchronous call is performed in a service chain or the
need to defi ne a policy to deal with the data referenced by the URL contained
in the XML response fi le.
Another type of diffi culty that can arise during the development of
an SII is represented by the lack of supporting infrastructure for geodata
processing. An analysis of available frameworks for the orchestration of
Geospatial services can be found in Rautenbach et al. (2012) where two
different platforms are discussed and analyzed: the 52° North framework
and the Zoo project. The characteristics of these two solutions are tested by
using the production of thematic maps as case study. Both the frameworks
are operating system independent, available as open source and compatible
with the current WPS standard. The 52° North framework is Java based
and offers a web admin tool that helps the uploading of WPS processes,
an orchestration API and a graphical modelling tool for the organization
of the geoprocessing workfl ow. On the other hand, the Zoo project is made
up of three main components: the Zoo kernel, the Zoo services and the
Zoo API. The Zoo kernel is the module that allows the WPS creation and
management. The Zoo services communicate with the Zoo kernel and are
composed of two parts: a confi guration fi le that describes the service, and
the code that the fi nal user wants to turn into a Web service. Finally, the Zoo
API is a Javascript library that can be used for process creation and chaining.
The two frameworks are compared against a wide set of characteristics,
from the available documentation to the ease of integration with other GIS
applications. Each of them has strengths and weaknesses (e.g., the lack of
semantic information and support to the BPEL standard) but the results
show that it is possible to use OGC standards such as WMS, WFS and WPS
in order to orchestrate a thematic map service.
A more detailed example of OGC services orchestration to produce
thematic maps can be found in Rautenbach et al. (2013). In addition to the
traditional OGC services, for the development of thematic Web services
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