Global Positioning System Reference
In-Depth Information
To achieve this goal, three mandatory operations are specifi ed:
GetCapabilities,
DescribeProcess that allows a client to request and receive detailed
information about processes that can be run on the service instance,
Execute that allows a client to run a specifi ed process implemented by
the WPS.
In the proposed example, based on the search for adequate evacuation
shelters in a bomb threat scenario, the authors fi rst show how the use of WPS
can supply all the traditional well-known GIS functionalities. Then, they
also point out the need to combine all the developed services to represent
them as a single application, which is the main idea behind the service
composition (Stollberg and Zipf 2007). To implement such a composition,
they observe that, although the specifi cation for the WPS mainly focuses on
the implementation of geoprocessing methods, there are no restrictions on
what can actually be implemented as a “WPS process”, that is a WPS can
also be used as a service that coordinates an orchestration of geographic
Web services (Stollberg and Zipf 2007). Moreover, they observe that by using
WPS for composition purposes, three different approaches are possible.
The fi rst two belong to general categories known as Centralized Service
Chaining and Cascading Chaining. In the former, a single service controls
the entire workfl ow invoking all other services in order to achieve a goal;
in the latter, services communicating each other can directly exchange data.
It is clear that these concepts are quite similar to the general defi nitions of
orchestration and choreography. The third option available with WPS is to
combine all functionalities into a single WPS implementation.
The ability to compose and orchestrate OGC services is of paramount
importance for the development of Spatial Information Infrastructures (SII),
distributed systems based on SOA principles that allow the processing
of spatial data in order to provide useful information to the fi nal user
(Rautenbach et al. 2013).
Some guidelines that describe the general structure of a service-
oriented SII can be found in an OGC best practice paper (Whiteside 2005)
which 'summarizes the most signifi cant aspects of the Open Geospatial
Consortium (OGC) web services architecture'. The proposed architecture
is based on the following properties (Whiteside 2005):
a) A multiple tiers subdivision of the various service components.
b) Support for Transparent, Translucent or Opaque service chaining.
c) Use of open standards for the defi nition of the service interface.
d) Use of open Internet standards for the service communication.
e) Independence from specifi c hardware or software platforms.
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