Paper 1

Helbig, Hermann and Marion Schulz (1997). Knowledge representation with MESNET: A multilayered extended semantic network. In Proceedings of the AAAI Spring Symposium on Ontological Engineering, pp. 64-72. Stanford, California.

What is MESNET?

A multilayered extended semantic network. In which nodes are concepts and edges are relations/functions among concepts.

Goal of Mesnet: KRL for NLU (uses the term interlingua like in machine translation)

Criteria to compare KRLs:

  • universality domain independent
  • homogeneity usable to describe the sense of words, sentences and dialogues.
  • cognitive adequacy "concept or object centered representation"
  • interoperability it can be used to represent info in all components of a NLU system (lexicon, inference, grammar, generation)
  • communicability easy to understand (without confuzion)
  • automatizability feasibility of automatic knwoledge acquisition techniques.

Structure of Mesnet: figure 1 from the paper.

  • sort/feature:
    • sort: hierarchy, must have category. not combinable (exclusive?).
    • feature: polyhierarchy, typical category. combinable.
  • multidimensionality of each node:
    • intensional/extensional: few attempts? (compared to what? modal logic seems to be based on that distinction, no?). Called preextensional because an extensional concept is normally not fully expressed but expressed only by few examples. Interesting part, talking about the example "nearly all girls in the class love a boy". Intensional layer: condensed info. Extensional layer: all info.
    • determinate/indeterminate: attributes REF={DET, INDET} and VARI={VAR, CO}. For example, a determiner that has an indepedent reference (i.e. a constant, even Skolem) will have REF=DET and VARI=CO. Something depending on something else (i.e. a skolem function) will have REF=INDET and VARI=VAR. (examples of intermediate situations?)
    • generic/non-generic: attribute GENER={GE,SP}. properties of a generic (GENER=GE) are inherited by default (typical or non-categorical, non-monotonic) by individuals of that class.
    • virtual/real: attribute "FACT", real for concepts that exists, virtual for hipotesized concepts. See figure 6.
    • order: attribute ORDER, Classifies different types of collective nouns. s^(0)=single entities. s^(1)=sets of entities, s^(2)=sets of sets of entities (on the extensional layer).
  • edges and subnets (See figure 5 for an example using relations/functions and shells):
    • relations/functions: various types, see the paper. To each relation/function is associated a set of inference rules in FOL. About 110 total number of relations/functions. Every thing is a concept, no need for explicit reification: Ax Ay ((x CAUS y) -> (x ANTE y))
    • shells (subnets): See figure 7. interesting example of what knowledge to use for answering the questions: "what is an house?" and "what did Peter buy?".

Comparison

Claims of beeing better than DRT (discourse representation theory) and GQT (generalized quantifier theory) because:
  • homogeneity
  • cognitive adequacy

Also, better than DRT and FCT (file change theory) because of shells.

In the conclusions it says that it can express donkey sentences (what is "combined quantification"?)

Observations (starting points for discussion)

the initial list of properties of a knowledge representation language are good, but: what is the cognitive adequacy thing?

But how do you produce that representation from normal NL? Example: "the lion is dangerous", "the lion is a mammal". First generic, second no.

Example in figure 3. How do you express "John gave Mary several dollars", "It was more than John gave to another girl" and "Two of them were counterfeits".

Interesting classification of KRLs for NLU in the conclusion.

Further reading necessary to see what they are able to do now, there are implemented systems (apparently, still to check).

Further readings

Ronald J. Brachman. On the epistemological status of semantic networks. In N. V. Findler, editor, Associative Networks: Representation and Use of Knowledge by Computers, pages 3--50. Academic Press, New York, NY, 1979.

Something on DRT, from this paper: Kamp, Hans (1981). "A Theory of Truth and Semantic Representation" in Formal Methods in the Study of Language, J. Groenedijk, J. Janssen, M. Stokhof, eds. Amsterdam: Mathematical Center Tracts.

Carnap: meaning and necessity (ref 5 in this paper)

-- FabrizioMorbini - 24 Oct 2006

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