Geoscience Reference
In-Depth Information
The second step determines a symbolic representation for each of the candidate
SFs and TFs identified earlier. We design semantic patterns and implement them with
definite clause grammars (DCGs): a recursive semantic analysis of each SF and TF
matches ASFs, RSFs, ATFs and RTFs. Therefore, anytime a spatial or temporal
relationship is found out, the corresponding RSF and RTF is analyzed and tagged
(i.e., adjacency, inclusion and orientation with an SF or a TF). Similarly, a second set
of DCGs is dedicated to the categorization of the SFs and TFs nature (e.g. oronym,
hydronym, town and road tags characterize SFs; day, week, month, season, year and
decade tags characterize TFs). Thus, for example, the noun phrase “to the north of
the torrent of Pau” is annotated as RSF with an orientation spatial relationship:
north tag and a category: hydronym tag. This RSF is defined recursively from the
ASF of toponym torrent of Pau. Each of these tagging processes is supported by
specific ontological resources [KER 09].
The third step interprets the symbolic representations obtained and calculates
numericrepresentations.Theinterpretationissupportedbyapproximationalgorithms
that associate timestamps with the TFs [LEP 07] and spatial footprints with the
SFs [FU 05, GAI 08, LIU 09]. The spatial approximation process involves resources
like the PostGIS
26
GIS, as well as gazetteers (e.g. database BD NYME
®
of the IGN,
GeoNames and local collaborative resources) in order to validate and retrieve each
ASF geometric representation. The spatial relationships (e.g. orientation: north) are
processed and corresponding representations are approximated. GIS operators (e.g.
translation, intersection) are applied to the reference SF. For the temporal
approximation, using the same principle, a period is initially associated with each
ATF and then the temporal relations (e.g. adjacency: toward) are interpreted and one
or more timestamps are calculated from the reference TF. A spatial index and a
temporal index are the result of this third step. The spatial index describes each SF
with the geometry, the phrase and the identifier of the corresponding paragraph and
document. Similarly, the temporal index describes each TF with the period, the
phrase and the identifier of the corresponding paragraph and document.
Both spatial and temporal processing flows are described in a detailed way in
[LES 07] and [LEP 07], respectively. Each detected SF and TF is represented by an
instance of the model shown in Figure 2.5. The calculation of the spatial and
temporal representations relative to the RSFs and RTFs is supported by algorithms
specific to each modeled spatial and temporal relation. Figures 2.7 and 2.8
schematize the reasoning: the reference site is illustrated in dark-gray and the target
is represented in light-gray. It is build by enlargement, reduction and movement of
the site.
Figure 2.7 illustrates the different interpretations planned by the implementation
for the five spatial relations defined in the core model. For adjacency, the bounding
box of the reference site, of side-length c, is extended by a factor of c/2 on each side.
For inclusion, the sides of the bounding box of the reference site are reduced by c/2.
26 http://postgis.refractions.net.
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