Geographic Reference Analysis For Geographic Document Querying

The work presented in this paper concerns Information Retrieval from geographical documents, i.e. documents with a major geographic component. The final aim, in response to an informational query of the user, is to return a ranked list of relevant passages in selected documents, allowing text browsing within them. We consider in this paper the spatial component of the texts and the queries. The idea is to perform an off-line linguistic analysis of the document, extracting spatial expressions (i.e. expressions denoting geographical localisations). The point is that such expressions are (in general) much more complex than simple place names. We present a linguistic analyser which recognises them, performing a semantic analysis and computing symbolic representations of their "content". These representations, stored in the text thanks to XML annotation, will act as indexes of passages with which queries are compared. The matching of queries with text expressions is a complex process, needing several kinds of numeric and symbolic computations. A prospective outline of it is described. 1 Presentation of the GeoSem project. Passage extraction from geographical document The work presented in this paper concerns Information Retrieval (IR) from geographical documents, i.e. documents with a major geographic component. Let’s precise at once that we are mainly interested in human geography, where the phenomena under consideration are of social or economic nature. Such documents are massively produced and consumed by academics as well as state organisations, marketing services of private companies and so on. The final aim is, in response to an informational query of the user, to return not only a set of documents (taken as wholes) from the available collection of documents, but also a list of relevant passages allowing text browsing within them. Geographical information is spatialised information, information so to speak anchored in a geographical space. This characteristic is immediately visible on geographical documents, which describe how some phenomena (often quantified, either in a numeric or qualitative manner) are related with a spatial and also, often, temporal localisation. Figure 1 gives an example of this informational structure, extracted from our favourite corpus (Hérin, 1994), relative to the educational system in France. As a consequence a natural way to query documents will be through a 3-dimensional topic, Phenomenon-Space-Time as shown in Figure 2. The goal is to select passages that fulfil the whole bunch of criteria and to return them to the user in relevance order. The system we designed and currently develop for that purpose is divided in two tasks: an off-line one, devoted to linguistic analysis of the text, and an online one concerning querying itself. Let’s give an overall view of the process, focusing on the spatial dimension of texts and analysis. Other aspects of the project, including especially the analysis of expressions denoting phenomena, techniques used to link the three components of information (Space, Time, Phenomena) and implementation issues can be found in (Bilhaut, 2003). Concerning text analysis, the goal is to locate, extract and analyse the expressions which refer to some geographical localisation 1 so that they act as indexes of text passages. The first remark to do is that we have to cope (in general) with complex nominal expressions, not only named geographical entities, as exemplified in figure 3. Indeed the collection of (proper) place names can Temporal expressions (expressing temporal localisation) are treated in a similar manner. Edmonton, May-June 2003 HLT-NAACL 2003 Workshop: Analysis of Geographic References , pp. 55-62