Synopsis

Chart Mapping is a mechanism for the non-monotonic, rule-based manipulation of chart items that are described by feature structures. There are currently two chart mapping phases during parsing:

1. Token Mapping, where input items as delivered by external preprocessors are adapted to the expectations of the grammar. This requires that input items are described by feature structures ‒ the token feature structures.
2. Lexical Filtering, where lexical items can be filtered by hard constraints after lexical parsing has finished.

Token mapping necessitates that tokens are described by feature structures. Token feature structures can be arbitrarily complex. This allows users to pass information of various preprocessing modules into the parser. To this end, a new format ‒ the XML-based FSC input format (PetInputFsc) ‒ was created. However, there is also a compatibility layer for the old input formats in PET, which transparently converts the token information available in these formats (form, optionally stem, characterization information and pos tags) into token feature structures. Please see the PetInput page for more information.

Another related issue is a new way of generic lexical instantiation which has been introduced with token feature structures and chart mapping. In this new setup, the parser tries to instantiate all generic lexical entries for each word. Upon lexical instantiation, the token feature is unified into a designated path of the lexical entry. Only if this unification succeeds, the lexical item is instantiated. In order to control the instantiation of generic lexical entries, the token feature structures are appropriatly constrained in the generic lexical entry, for instance by requiring that a generic verbal entry is only applicable for token feature structures where the highest ranked part-of-speech tag is a verb.

Implementation status

• Chart mapping is part of the PET main branch since August 2010.
• Chart mapping is not yet implemented in LKB.

Documentation

Tutorial: http://www.delph-in.net/2009/cm.pdf

Publications

Adolphs, Peter; Oepen, Stephan; Callmeier, Ulrich; Crysmann, Berthold; Flickinger, Dan & Kiefer, Bernd. 2008. Some Fine Points of Hybrid Natural Language Parsing. In: Proceedings of the Sixth International Language Resources and Evaluation (LREC-2008). Marrakech, Morocco. 

@inproceedings{adolphs_fine_2008,
  address = {Marrakech, Morocco},
  title = {Some Fine Points of Hybrid Natural Language Parsing},
  url = {http://www.lrec-conf.org/proceedings/lrec2008/pdf/349_paper.pdf},
  booktitle = {Proceedings of the Sixth International Language Resources and Evaluation {(LREC-2008)}},
  author = {Adolphs, Peter and Oepen, Stephan and Callmeier, Ulrich and Crysmann, Berthold and Flickinger, Dan and Kiefer, Bernd},
  year = {2008},
  keywords = {chart mapping, hpsg, preprocessing}
}