Database Server Models for WMS and WFS Geographic Web Services - Geographical Information Systems: Trends and Technologies - page 151

applied. During a transformation, the system is in charge of the coherency
of the dataset.
Proposed operations to manage the conceptual schema are applied
on classes (in the sense of object oriented modeling), attributes, objects
and relationships. The language allows manipulations upon classes
with the definition of aggregates, renaming, deletion, specialization
and generalization; upon attributes, with renaming and deletion; upon
objects with aggregation and fi lter; upon relationships, with creation and
deletion.
Some perspectives of this work are the semi-automation of the fi nal
schema, the use of web services to transform database schemas (direct or
indirect—i.e., issued of a web service) or a standard manipulation to provide
a predefi ned structure as results of the transformation.
One of the main differences between the approaches developed in
(Staub 2007; Staub et al. 2008) and (Bucher and Balley 2007) is based on
the transformation specifi cation. Staub's approach relies on a mapping
specification from the initial schema to the destination schema. The
mapping is defi ned with selection and transformation operators. The
user specifi es transformations based on schema manipulations instead
of defi ning an imperative approach of restructuring tasks. This approach
has a better relevance whenever the destination schema is known and the
transformation specifi cation is based on a method rather than operations.
The mix of these two approaches leads to promising perspectives.
Synthesis
Described propositions show weaknesses on the topic of data semantics in
web services. OWS such as WMS and WFS are database schema dependent.
OWS offer a syntactical interoperability (e.g., data exchange) but nothing
about semantic representations (e.g., data model relationships). Conceptual
data models are hidden, and semantic transformations are not available.
One of the reasons may be similar to the introduction of external schemas
in relational databases (i.e., view mechanism). The lack of semantic tools
may be another one. We propose to reduce the second one by providing a
way to introduce semantic aspects while exchanging data.
WMS services mainly provide graphic results since WFS deals with data
access. The visual aspect, rather than complex functions, should be kept
in mind while evaluating consultation tools based on Internet solutions.
The choice is based on requirements and constraints on services: simple
consultation (data and interactions with images) or real integration of data
sources in complex applications (i.e., interactions with data based on the
CRUD paradigm).