Global Positioning System Reference
In-Depth Information
Systems (GIS), where this new computing model would represent a possible
solution to some of the classic problems due to the complexity of geographic
information, such as retrieving of geographic data, accessing newer
versions of the same information and, above all, supporting geographic
interoperability (Zhao et al. 2007). In fact, before the massive spread of
SOC, a user wishing to access geographic data could either download
an entire dataset or require the data provider to send such a dataset on a
digital or magnetic medium. Typically, the end user was also provided with
a catalogue to look for desired data (Zhao et al. 2007). However, a similar
approach presented some important problems. First of all, the geographic
information was provided in a proprietary format whose granularity often
did not coincide with the real user's needs and did not allow for data
sharing. Moreover, an additional drawback was related to the geographic
information validity, which might be out-dated or not updated to the latest
version (Zhao et al. 2007).
As known, being based on open standards, accessible by anyone,
geographic services are at the base of the revolution of how spatial data
are obtained and processed. However, as autonomous building blocks,
services have to be properly managed when combined to realize complex
systems. In the following subsection, a way to integrate different services
is presented.
Service Oriented Architectures
SOA 'represents a model in which automation logic is decomposed into
smaller, distinct units of logic' (Erl 2005). In its simplest implementation,
SOA defi nes an interaction among software agents as a simple exchange of
messages among different participants. In particular, a basic implementation
of a SOA is a relationship among three kinds of participants, namely the
service provider, the service registry and the service requestor (the client). A
desirable characteristic is the ability of the messaging framework to preserve
the low coupling property. In fact, as soon as a service sends a message it
loses control of what happens to the message itself. Moreover, to facilitate
services interaction a type of inter-service communication infrastructure
is also required. The Internet is the most commonly used communication
infrastructure. Services that make up a SOA exhibit the following main
characteristics (Papazoglou and van den Heuvel 2007):
all functionalities in a SOA are defi ned as services;
all services are autonomous;
the service location is irrelevant.
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