Database Reference
In-Depth Information
local to the global level, in an inter-operable way for a variety of uses. Discovery is performed through
services that should follow INSPIRE standards and can be implemented through some products (either
proprietary or not) that declare their compliance.
Nevertheless, current technologies adopted in SDIs, and consequently the actual practice for searching
geographic information, do not comply with the way users express their needs and search for informa-
tion and hamper the ability and practices of geodata providers.
One main problem is due to the characteristics of the information on the available geodata, i.e., meta-
data. Metadata is an essential requirement for locating and evaluating available geodata, and metadata
standards can increase and facilitate geodata sharing through time and space. For this reason considerable
efforts have been spent to define “standard” and minimum core metadata for geodata to be used in SDIs.
INSPIRE is nowadays a directive of the European community that comprehends metadata specifications
(European Commission, 2009).
Nevertheless, such specifications are still incomplete and inadequate for they do not allow specifying
all the necessary information on geodata as far as the temporal dimension, and force providers to generate
precise metadata values, which are missing in many real cases (Dekkers, 2008; Bordogna et al., 2009).
This chapter, analyses the utility of temporal metadata on geodata and proposes a framework to rep-
resent its imprecise and uncertain values as well as to express its possible multiple semantics..
Another problem with the current information search practice in SDIs is that the user is forced to
express precise conditions on the metadata values that must be perfectly satisfied in order to obtain a
result. Further, the results are unordered, with no indication of relevance to the user who must access
the remote geodata to become aware of its actual adequacy to his/her needs. Even when a web service
is invoked, this may case useless network overloading.
A framework that this chapter proposes for optimizing this search practice is to allow users to express
flexible queries, with tolerant (soft) conditions on the metadata values, so as to retrieve results ranked
in decreasing order of their satisfaction to the query.
To this aim the fuzzy database framework can provide an effective way to model the discovery
service of SDIs, since it allows both representing and flexibly querying imperfect metadata (Bosc and
Pivert, 2000).
In the next paragraph, this chapter will discuss the limitations of current temporal metadata in discovery
services of SDIs and propose some solutions. Then, the proposal of a formal and operational method to
represent imperfect temporal metadata values and allowing users to express soft search conditions, i.e.,
tolerant to under-satisfaction, is presented. In doing so, discovery services can apply partial matching
mechanisms between the “desired” metadata, expressed by the user, and the archived metadata: this
would allow retrieving geodata in decreasing order of relevance to the user needs, as it usually occurs
on the Web when using search engines. In the last paragraph, the proposal is illustrated with an example,
while the concluding paragraph describes the context of this research work.
ARCHITECTURE OF A SPATIAL DATA INFRASTRUCTURE
An overview of the current understanding of the technical architecture of INSPIRE is depicted in figure
1; it has been adopted by the European SDI (for a through description of this figure, see INSPIRE Cross
Drafting Teams, 2007). It is a layered structure that makes available several facilities executed by the
functional components (depicted by the rounded boxes).
