International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B2. Istanbul 2004
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Figure 1. Geoinformation Service Infrastructure
Large geo-processing tasks are achieved by combining or
chaining artefacts located along the distributed nodes. Such
combinations of artefacts provide diverse functionality that
satisfies particular sets of requirements. Every artefact has an
economic value; these artefacts are assembled to perform
operations within the infrastructure, resulting in a specialised
artefact that has a value equal or larger than the value of the
artefacts used. This architectural approach can be regarded as a
“value-added system”. By chaining these artefacts one can
provide a service. A service is defined as a behaviour of value
to the user, which is accessible or instantiated through
interaction points. This behaviour is exhibited through an
appropriate combination of elementary artefacts.
In order to bind multiple artefacts into a chain that
accomplishes a large geo-processing task, a proper description
of the participating artefacts is required. These descriptions
focus on exposing the artefact’s internal behaviour, its intended
effect and its interaction points or points of composition. These
descriptions, which are presented as instances of well-defined
models, make it possible to interchange and reuse artefacts. We
call these descriptions system metadata and they are stored and
accessible through a service repository.
The GSI system enables Geo-Service Providers (GSPs) to make
use of each others functionality to supply a wide range of
services and possibly to reach larger groups of users. Figure 1
illustrates the interactions that take place as GSP nodes provide
services to their users.
Users interact with the different GSP-nodes to request their
specific services. Figure 1 shows these interactions as dashed-
lines. GSP-nodes may make use of artefacts available in other
GSP-nodes in order to realise a particular service. These
interactions between GSP-nodes are shown in Figure 1 as solid
lines running from Node to Node. All connections mentioned
here are established through a network.
At the bottom of Figure | we can see that additional data
collections located at non-GSP nodes may still be accessed, if
needed, either by users or service providers. This is achieved by
making use of the conventional data discovery functionality, of
the clearinghouse server. These interactions appear in the
Figure | as dashed-dot-lines.
196
4. MODELING THE GSI AS VIRTUAL ENTERPRISE
Looking at the GSI as a VE facilitates its development and
maintenance as it can be seen as an enterprise entity to be
analyzed, modelled and executed with concepts from enterprise
modelling and engineering where an enterprise is described by
different inter-related models to describe its various essential
aspects.
The integrated enterprise model of VE (and associate
specifications) will describe the system from various
perspectives (viewpoints) in order to provide the focal point,
around which the business operations in VE are designed,
implemented, managed and improved and/or business
opportunities are identified. It will also support the assessment
of its performance in ‘totality’ along the various operational
dimension, i.e. quality, time of delivery, cost, optimum use of
resources, monitoring of changes in the surrounding
environment as well as the capability to adapt to such changes
at both organization’s business and operational levels. The
model plays a vital role in enterprise integration and managing
virtual enterprises. It represents the common semantic to insure
interoperability and knowledge sharing between its functional
entities for the execution of business processes.
The Geo-spatial Industry can benefit from the various models
and tools that are developed in other industries, as well as the
vast opportunities offered by ICT, to make such a ‘virtual’
enterprise VE feasible. These models define a set of
abstractions (viewpoints) of an enterprise with the associate
viewpoint languages defining the concepts of each viewpoint
(31, [9].
With respect to the computational viewpoint (as the most
relevant to our discussion), it provides functional
decomposition of the system into a set of services that accessed
through interfaces (set of operations that characterize the
behaviour of an entity). Processes are modelled by their
properties (content, behaviour, environment of a service), also
describing the technology, information and enterprise aspects of
the service (the process Model). Services can be classified
according to several schemes [2], [11].
e Stakcholders perspective: processes performed by Service
Provider, Service Requestor, Service Broker:
» Functionality perspective: Data Services (to access to
databases), Registry Services (to document and/or locate
data and processes), Map Services (perform basic
mapping operations such as georeferencing,
visualisation), Application Services (value added
services);
e Hierarchy and Chaining Perspective: Simple Services,
Aggregated Services (bundle pre-defined chain of
services, to be presented as one), chaining services
(design interfaces between chain of services), Mediator
(smart) Services (support chaining of services according
to user requirements), Workflow Management Services
(pre-defined chain of services, managed by computer-
based workflow management system).
5. THE GSI BROKER
In a virtual environment, with enterprises not knowing each
other, there must be a mechanism to facilitate their cooperation.
For that the broker can be used. A broker in the VE context is
the facilitating mechanism to find partners to cooperate with
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