Global Positioning System Reference
In-Depth Information
(population, surface (SR))) = density. The source attribute “population”
semantically determines the method “density (integer, real)”. This method
has the following parameters: the attribute “population” and the result of
the method “surface (SR)”. The target attribute, here called “density”, is
provided as a new attribute in the fi nal schema as a conventional attribute.
It can thus be directly provided in complement of data schema information
given by the WMS/WFS operations GetFeature or GetFeatureInfo.
Operational complexity concerns the complexity of the applied
methods. In the case where a method has parameters that are results of
methods, operational complexity will be aligned with the complexity of
these methods.
We emphasize here that there are two approaches to the determination
of methods. The fi rst approach is to use external services. WPS (OGC
2007b), defi nes the meaning of rules to set up and to run a geo-processing
as a Web service. The user executes in this case a geospatial operation,
with all necessary data. The server starts the process and informs the user
of its progress. An architectural alternative to this approach is given in
Grosso et al. (2009) or Stollberg and Zipf (2007) with an orchestration of
services. The second approach is internal and is linked to the database. Our
proposal is oriented towards the second approach. These two approaches are
complementary in the sense that the method could be the implementation
of a Web service request (e.g., a WPS). The Web service is an encapsulation
of the method and the method or the WPS are hidden to fi nal users.
Relevant Link RLextA-A
A RLextA-A links leads to additional attributes in the fi nal schema, which
are retrieved from one or more classes.
A RLextA-A link binds two sets of attributes (possibly reduced to a
singleton) of different classes. The classes involved in these links may be
of relevance related among others, through the inheritance relationship,
composition or be completely independent in the conceptual data schema.
This RL is defi ned with a spatial operator in order to make an independent
connection between different classes of the data model. It therefore
represents a semantic spatial link.
RLextA-A is defi ned by the following elements: the class concerned
by the RL (named of source class), the set of source class attributes, the
target class, the relevant target class attributes, the spatial query involving
the source class and target class. Table 6 presents the formal defi nition of
RLextA-A.
This defi nition means that in a schema where exists the set of attributes
{a s1 ,..., a sn } of a class c i , this RL adds in the fi nal schema the set of (target)
attributes {a t1 ,..., a tm } of the class c j .
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