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FOSS4G2006 - Free And Open Source Software for Geoinformatics
FOSS4G2006 - Free And Open Source Software for Geoinformatics
11-15 September 2006 Lausanne, Switzerland
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Combining Logical Information Systems and OpenGIS tools for geographical data exploration
The amount of geographical data available around the world is ever increasing. This
makes information retrieval a significant stake in geomatics. Traditionnaly,
geographical data are organised as layers of information. However, the layer model is
a rigid structure for navigation, as it does not permit to reorganize information
beyond predefined thematics. Spatially extended SQL languages offer expressive
querying capabilities that could balance layer navigation. However, building relevant
queries often require external knowledge on the data. Recently, Logical Information
Systems (LIS) introduced a new paradigm for information retrieval. In LIS,
information is described by logical descriptors which are also used as arguments in
data navigation and querying. These systems do not rely on a hierarchical data
organisation and enable to tighly combine flexible navigation and expressive querying
in the information search process. In this paper, we present GEOLIS, a prototype
combining LIS and webmapping capabilities for geographical data exploration. The
storage component of GEOLIS is LISFS, a generic implemention of LIS that takes the
form of a genuine Linux file system. An important feature of LISFS is that it permits
navigation and querying among a set of files as usual and inside files. The second
service, called Part-of-files File System (PofFS) is used in GEOLIS. Geographical
data are accessed through a graphical web interface designed for data navigation.
This interface includes MapServer technology for map vizualisation and PHP based
components for logical navigation. The Geographical Markup language (GML) and the
OGR2OGR library offers a flexible data format, which is appropriate for interactions
between MapServer and LISFS.

Data handling with LIS provides new functionnalities in data exploration. Indeed,
logical descriptors used to describe data in LIS also play the role of navigation
links and form the basis of the querying language. This enables to freely combine
querying and navigation operations in the search process. For instance, a subset of
data selected by a query could then be reduced using navigation links, which will
refine the query. The resulting subset can be used as a new start point for querying
or navigation. Furthermore, LIS offer an assisted navigation. At each step of the
search process, the system suggests the user navigation links, and guaranties that
each proposed link reduces the current substet of data but does not lead to an empty
set. GEOLIS combines geo visualization capabilities with LIS functionnalities in
order to connect map representation and navigation with logical exploration of
geographical data.

GEOLIS works with vectorial geographical data. It does not require to convert
geographical data in a particular format. An existing geographical format can be used
as soon as LISFS has been equiped with the corresponding transducer. A transducer is
a plugin that extracts properties from parts of the geographical data. This mechanism
makes GEOLIS open on several data sources. At the moment, GEOLIS prototype supports
GML. GML is supposed to become a standard for geographical data sharing and has the
avantage to gather all information in one file. As it is a subset of XML, writting a
GML transducer based on XML-schema and XSLT is quite a simple task. Futhermore, each
view in the PofFS is a syntaxically correct GML file, which can be accessed by
MapServer (or other applications) through connectors like OGR2OGR. This is made in a
transparent way, and views appear as traditionnal Geographical Information Systems
(GIS) layers. As views are handled at the file system level, navigating in
geographical data corresponds to browsing directories in LISFS. This is done in
GEOLIS using a PHP based interface. GEOLIS has been tested on a real dataset about
rodents distribution in the Sahelo Soudanian Africa. This database represents a large
dataset : about 20,000 features with a mean of 39 attributes per feature. It is also
composed of heterogeneous data : several attributes are not filled for many rodents;
furthermore, half of the base has been collected in Senegal whereas the studied area
goes far East to Chad.. Experiments have enabled to detect quickly anomalous entries
in the dataset, e.g. individuals with incoherent values (numerical values to qualify
the genus of some rodents) or uncertainty on values ( values including or equals to
'?'). These entries appear isolated in the logical navigation, which is useful for
database cleansing.

To conclude, our prototype shows that LISFS cohabits well with existing mapping
technologies. It provides directly, i.e. without implementing specific drivers, new
services to mapping applications. First of all, it offers a new navigation paradigm
that can be connected, or not, with traditionnal map navigation. Furthermore, it is
appropriate for managing heterogeneous data and cleansing them. In the future, we
plan to work on spatial logics to improve expressiveness and querying capabilities of
GEOLIS with predicates including distance and topological relations. We also have in
mind to connect LISFS with other GIS tools to take advantage of LIS view management,
for inserting and updating features.
Id: 131
Place: Lausanne, Switzerland
Room: Amphimax (MAX 415)
Starting date:
15-Sep-2006   09:30
Duration: 30'
Contribution type: Conference
Primary Authors: Mr. BEDEL, Olivier (IRISA Rennes / Université de Rennes 1)
Co-Authors: Mr. RIDOUX, Olivier (IRISA Rennes / Université de Rennes 1)
Mr. QUESSEVEUR, Erwan (Laboratoire Reso / Université de Rennes 2)
Presenters: Mr. BEDEL, Olivier
Material: slide Slides
Included in session: Session 14 Development

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