I came accross an exciting paper by Karin Verspoor, George Papcun and Kari Sentz from LANL. The authors suggest a motivation for the so-called shallow approach to Information Extraction.

Indeed, an ongoing discussion between ‘deepers’ (who argue for a deep and presumably full semantic and syntactic analysis) and ’shallowers’ (who argue for a shallow analysis) revealed that “[s]hallower approaches are more robust to the linguistic variance of free text”, but “they are much faster”, while “[d]eeper approaches … are in principle more domain-neutral because they embody general linguistic principles”, but they are obviously much more expensive both in throughput and development time. I’ve got a particular interest in this issue, because in Ontos we use a kind of shallow approach, and we really do not attempt to get a full syntactic and semantic analysis. Our rules and patterns primarily focus on the recognition of objects and relations represented in the domain ontology.

Verspoor et al. 2003’s motivation relies on the Construction Grammar’s (CG) hypothesis that constructions are the essential linguistic units stored in the human mind. The basic notion of construction is defined in the following way:

C is a construction iff C is a form-meaning pair F_i, S_j>, such that some aspect of F_i (form) or some aspect of S_j (semantics) is not strictly predicted from C’s component parts or from other previously established constructions.

The main argument of constructionists is that in natural language there is a wide range of non-compositional expressions (e.g. idioms), which should be stored in the lexicon. As far as I understand, the radical constructionist view is that any linguistic structure (w.r.t. its syntax and semantics) is a construction. Although the authors note that CG does not entirely reject the principle of compositionality adopted in formal semantics, this principle does not in fact play an important role in CG. Furthermore, the authors suggest that gazetteer entries and expressions captured by syntactic patterns for named entities in a shallow NLP, are constructions in the sense of CG.

I would not be so enthusiastic with the issue of (non)compositionality in the field of IE. Presumably, using gazetteers has nearly nothing in common with (non)compositionality of their entries. In fact, most entries of key-gazetteers (those providing context information) are splendidly compositional (cf. international company, regional hospital), and e.g. patterns using any output of the Morphology Component (i.e. specifying just grammatical features and order of their units) produce also compositional phrases.

But still, there is a special subfield in our NLP, where patterns (not gazetteers) do involve a kind of non-compositional phenomena. I’ll write about it in the next post.