Database Reference
In-Depth Information
Figure 2. Components of a generic retrieval model
selection conditions and resource descriptions must be expressed in the same formal representation at
some stage of the matching process.
In particular, in the discovery of geodata sets, the query selection conditions expressed by a user
should clearly specify “what” is of interest through content keywords (e.g., landslides), “where” the
interesting features should be located (e.g., in a bounding box surrounding the Alps), “when” these
features should have been observed (e.g., the date/s of the observation), and “why” they are searched
(e.g., to detect recurrence of landslides).
On the provider side, metadata should describe georesources following the same four aspects.
TEMPORAL METADATA IN THE EUROPEAN SDI
Within the context of a SDI discovery service, temporal aspects play a major role at multiple levels,
especially when considering some outstanding applications of geodata that involve dynamic phenomena.
This is the case of research on climate change, meteorological forecast, monitoring the impact of natural
and anthropic events on the environment, etc.
In the perspective of the hugely populated European SDI envisioned by INSPIRE, it is necessary
to filter out geographic resources that not only refer to a given spatial location, but also match both
the temporal coverage of interest and the temporal resolution suitable to the application purposes. This
implies an adequate temporal description by the metadata providers, who should be guided in character-
izing their resources as far as their temporal aspects, also when temporal descriptions cannot be precisely
assessed (such as for resources regarding the past).
Recommended temporal specifications in the Implementing Rules of metadata in INSPIRE (European
Commission, 2007) are listed in Table 1.
They are inadequate to satisfy the multiple semantics of the temporal conditions. In fact, they are
mainly devoted to time stamping resource lifecycle, while only the element ”Temporal extent” contains
dates related to the resource content whose meaning is ambiguous and does not help in characterizing
both temporal coverage and resolution.
To improve temporal metadata definition, some proposals have been formulated and a set of six new
recommendations is now available (Dekkers, 2008). Their main role is to specify the type and format
