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Generation of Referring Expressions: the State of the Art SELLC Winter School, Guangzhou 2010 Kees van Deemter Computing Science University of Aberdeen.

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Presentation on theme: "Generation of Referring Expressions: the State of the Art SELLC Winter School, Guangzhou 2010 Kees van Deemter Computing Science University of Aberdeen."— Presentation transcript:

1 Generation of Referring Expressions: the State of the Art SELLC Winter School, Guangzhou 2010 Kees van Deemter Computing Science University of Aberdeen Guangzhou, Dec 2010

2 Reference to sets: taking stock Guangzhou, Dec 2010

3 Reference to sets: taking stock 1. Remarkably little computational or psycholinguistic work has been done on reference to sets. This stands in contrast to a significant amount of formal semantics work, mostly focussing on collectivity (e.g., Scha 1981, Link 1983) and intensionality (Landman 1989). 2. Problems with computational complexity are even greater than with reference to single objects (but only if brevity is an issue). – Most people agree that getting the right descriptions is a more important problem. Guangzhou, Dec 2010

4 Reference to sets: taking stock 3. Gardent (2002, ACL) criticised Van Deemter (2002) for producing overly elaborate descriptions. This can be partly prevented by logical optimisation. [Project: try this, for example using Quine/McCluskey optimisation.] Gardents own proposal re-instates Full Brevity. Constraint satisfaction techniques are used to combine declarative problem statement with (relatively!) fast search. Horacek (2004) has proposed alternative techniques for weeding out infelicitous descriptions. Also Gatt 2007 (PhD thesis). Guangzhou, Dec 2010

5 Reference to sets: taking stock 4. Evaluation of algorithms that refer to sets lags behind evaluation in GRE more generally. TUNA evaluation (Van der Sluis et al 2007, Gatt et al 2007) limited this to references to sets of 2. All algoritms performed badly. STEC invited people to submit algorithms that refer to sets, but none was received. Guangzhou, Dec 2010

6 Reference to sets: taking stock 5. Gatts work has put the spotlight on intra-NP coherence, e.g. the Greek and the Italian is better than the Greek and the cook Gatts research method is exemplary, and coherence might prove to be an important aspect of text quality more generally (also outside GRE). E.g., Coherence between different NPs: The Greek....; The Italian... Coherence between all the words in a text. For example, it seems plausible that all the words should have similar degrees of formality Guangzhou, Dec 2010

7 Reference to sets: taking stock 6. Collective reference. Stone (2000) proposes a (constraint-based) GRE algorithm that produces references like The parallel lines at the top of the screen ---------------------------- --------------- Guangzhou, Dec 2010

8 7. Logical completenes Why we added negation: generate a distinguishing RE whenever one exists Attempt at formalisation: A is complete with respect to logical language L iff A generates a distinguishing description whenever one exists in L. For example, using informal notation: L = Atom | L where L = L L (This is what Dale & Reiter aimed for, focussing on single referents) Guangzhou, Dec 2010

9 7. Logical completeness Alternatively, L = Atom | L where L = L L | L L | ¬L (Boolean descriptions without relations) Challenge to logicians: can we formulate logical completeness without dependence on some language L? What is the set of all possible distinguishing descriptions (with any connectives allowed)? Hint: Ren et al. (2010), for 2-place relations, use theory of Generalised Quantifiers Guangzhou, Dec 2010


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