DESCRIPTION OF DATA STRUCTURES AND INTEROPERABILITY
S. Balley
COGIT Laboratory, IGN, France
sandrine.balley@ign.fr
In this paper, a “data structure” means a set of schemas and rules characterizing a dataset at semantic, conceptual, logical and physical levels. Users of spatial data and processing services face three problems regarding data structures. Firstly, they must understand the structure of available datasets, namely the source structure. Secondly, they must understand the structure required by available processing services, namely the target structure. Thirdly, they must transform the source structure into the target structure. The first two problems call for adequate descriptions of structures, while the third one calls for adequate restructuration services. This paper reviews the contributions and insufficiencies of existing standards to describe structures and to assess required structure transformations.
To understand a source structure requires understanding the representation
process followed by the data producer, i.e. choices for categorizing,
selecting, modelling, and implementing real world entities into database
objects. Some of these choices can be documented following several ISO
standards: Metadata (ISO19115), Application schema (ISO19109), Spatial schema
(ISO19107), Specifications (ISO19131), etc. However, there is a lack for a
formal description of categorization and modelling choices, e.g. to specify
what is called “a road”, and what part of a road must be represented [Gesbert,
2004]. Furthermore, descriptions of different levels of a structure should be
linked together.
To understand a target structure firstly implies to know the application schema
of the data processing service, including the “role” of each schema element in
the process []. For instance, a route processing service requires
graph-structured data, and the “Arc_2” class refers to drivable sections
dedicated to the computation of secondary routes [Neun et al, 2006]. It
secondly requires understanding the grammar rules of the used platform, e.g.
whether it supports complex geometric primitives or not. Current models for
describing services like WSDL and OWL-S, currently enriched by on-going works
about service chaining [Lemmens et al, 2006], can describe some structure constraints.
However, the platform grammar rules and the “role” of application schema
elements need further formalisation.
To transform a source data structure into a target structure, i.e. to make data
and services interoperable, implies to match both descriptions. Therefore, this
paper argues for an integrated, ISO-based, description model for source and
target structures. As shown on figure 1, this model would give rise to a range
of interesting services dedicated to data producers, service providers, and
end-users, to edit, compare and transform data structures.
Figure 1 : Example of a
restructuration service to feed data processing services with data. The
restructuration service requires an interactive user parameterization.
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