Layout & Language: Preliminary experiments in assigning logical structure to table cells

Layout & Language: Preliminary experiments in assigning logical structure to table cells Matthew Hurst and Shona Douglas Language Technology Group, Human Communication Research Centre, University of Edinburgh, Edinburgh EH8 9LW UK {Matthew. Hurst, S. Douglas}~edinburgh. ac. uk Abstract We describe a prototype system for as- signing table cells to their proper place in the table's logical (relational) structure, based on a simple model of table struc- ture combined with a number of measures of cohesion between cell contents. Pre- liminary results suggest that very simple string-based cohesion measures are not suf- ficient for the extraction of relational in- formation, and that future work should pursue the aim of more knowledge/data- intensive approximations to a notional sub- type/supertype definition of the relation- ships between value and label cells. 1 Introduction Real technical documents are full of text in tabu- lar and other complex layout formats. Most repre- sentations of tabular data are layout or geometry- based: in SGML, in particular, Marcy Thompson notes "table markup contains a great deal of infor- mation about what a table looks like.., but very lit- tle about how the table relates the entries .... [This] prevents me from doing automated context-based data retrieval or extraction." 1 1.1 Views of tables In (Douglas, Hurst, and Quinn, 1995) an analysis of table layout and linguistic characteristics was of- fered which emphasised the potential importance of linguistic information about the contents of cells to the task of assigning a layout-oriented table repre- sentation to the logical relational structure it em- bodies. Two views of tables were distinguished: a denotational and a functional view. a(Thompson, 1996), p151. The denotation is the table viewed as a set of n- tuples, forming a relation between values drawn from n value-sets or domains. Domains typically consist of a set of values with a common supertype in some actual or notional Knowledge Representation scheme. The actual table may also include label cells which typically can be interpreted as a lexical- isation of the common supertype. We hypothesize that the contents of value cells and corresponding label cells for a given domain are significantly re- lated in respect of some measures of cohesion that we can identify. The functional view is a description of how the information presentation aspects of tables embody a decision structure (Wright, 1982) or reading path, which determines the order in which domains are accessed in building or looking up a tuple. To express a given table denotation according to a given functional view, there is a repertoire of lay- out patterns that express how domains can be grouped and ordered for reading in two dimensions. These layout patterns constitute a syntax of table structure, defining the basic geometric configura- tions that domain values and labels can appear in. 1.2 An information extraction task Our application task is shallow information extrac- tion in construction industry specification docu- ments, containing many tables, which come to us via the miracles of OCR as formatted ASCII, e.g., in Figure 1. The predominant argument …

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