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GlennSlayden edited this page Dec 13, 2011 · 12 revisions

This page discusses some of the known issues with paraphrasing, with especial reference to (R)MRS. It also tells you how to paraphrase using MRS in the LKB.

Paraphrasing in the LKB

Paraphrasing using rules

Put your paraphrasing rules in a file paraphraser.mtr, and load it in the lkb/script file.

;;; transfer rules for paraphrasing
#+:mt
(mt:read-transfer-rules 
 (list
  (lkb-pathname (parent-directory) "paraphraser.mtr"))
 "Paraphrasing Rules"
 :filter nil :task :paraphrase)

Then when you parse something, a menu item Rephrase should appear, and this will apply the paraphrase rules to the selected parse, and then generate from the paraphrase. If you don't get generated output, try first doing Start Server from the Generate menu.

Paraphrasing rules are done with the same transfer rules used in MT and generation. An example is given below. This will paraphrase "We gave a demo of the system" -> "We demoed the system".

give+demo_mtr := light_verb_mtr &
[ INPUT.RELS <! [ PRED "_give_v_1_rel" ],
                [ PRED "_demo_n_rel", ARG1 #arg1 ],
                [ PRED _of_p_sel_rel ], 
                [ PRED _a_q_rel ] !>,
  OUTPUT.RELS <! [ PRED "_demo_v_rel", ARG2 #arg1 ] !> ].

You also need to add the type definitions for the rules, in a file called mtr.tdl and load it in the script file. Note: copying this from the ERG is a good start, although your definition of *list* may be different (e.g., list).

You may also have to set up the translation grid parameter. For Jacy it is:

(setf *translate-grid* '(:ja . (:ja)))

This says that the grammar can act as a generator server for Japanese ourselves and will send off generation requests (from selection `Rephrase' on the parse summary view or `Generate' on the LOGON MRS browser) to a Japanese server, i.e. ourselves. likewise,

Paraphrasing using Underspecification

  • Underspecified lexical types (or rules) effectively lead to paraphrasing

    • parsing Which dog barked and then generating gives

      • Which dog barked?

      • What dog barked?

      • Which dog did bark?

      • What dog did bark?

General Discussion

From the meeting in Cambridge 2008-05-24

Dan showed off the paraphraser in the ERG.

  • the rules can rewrite features.
  • and whole clauses
  • they can be made bidirectional if there is no CONTEXT or FILTER
  • nice use of relational nouns in the light verb rule
    • "we gave a demo of the system" -> "we demoed the system"

Two current approaches

  • underspecification: in/on/at_rel
  • explicit mapping via rules

Uses of paraphrasing

  • we can map representations to a canonical form
    • e.g. reducing variation before we do a task such as MT
      • (the hourglass model)
    • not always possible
  • query expansion
  • relaxed input to the generator
    • e.g. allow "possible_rel" which maps to "can_rel" and "be_able_to_rel". Non-English users shouldn't have to care.

Who is working on Paraphrase/rule extraction?

What are some phenomena we can handle now? (can we map them to situation types: LH?)

  • light verbs,
  • compounds,
  • serial verbs,
  • classifiers,
  • alternations
  • relational nouns/prepositions,
  • modal verbs and tense/aspect,
  • "swim across the river"/"cross the river by swimming"
  • by/gerund,
  • verbal/nominal, "opening the door he found the revolver/he opened the door and
    • found the revolver",
  • done by underspecification --- adjective/adverb

Meta-discussion

  • currently we don't have perfect world models so we normally overgenerate and rank

    • want to be able to make things that work now && support deeper processing when people can do it (AAC)

    • the statistical models on overgeneration leads to models useful for analysis

  • good to map paraphrase classes to situation types not just syntactic types

  • sometimes we need anaphora resolution

    • "Tom ate because he was hungry" -> "Tom's hunger made him eat"
    • no-one is working on this within the lkb
    • we can do some of this with paraphrase rules

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