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Recursive transfer

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Contents

[edit] Todo

  • Make the parser output optionally original parse tree (SL syntax) and target parse tree (TL syntax).
  • Attribute structures. These are defined in typical .t1x format with def-attrs
  • Make the parser robust — we should never get parse errors, though our trees may be mangled.

[edit] Process

The parser has two trees, both are built simultaneously:

  • The source tree is parser-internal
  • The target tree is the "abstract syntax tree".

When a sentence terminal (S) is reached, the target tree is traversed and printed out.

[edit] Questions

  • What to do with a parse-fail.
    • Implicit glue rules
      • How do we make sure that we never get Syntax error (e.g. really robust glue rules).
    • the glue rules would not compute anything, just allow for partial parses
  • How about unknown words...
    • they would be some non-terminal UNK that would be glued  by the all-encompassing glue rule from above.
  • Ambiguous grammars -> can be automatically disambiguated ?
    • Learn shift/reduce using target-language information ?
  • Converting right-recursive to left-recursive grammars.
  • How to apply macros in rules which have >1 non-terminal.
  • What on earth to do with blanks / formatting...
  • Do we try and find syntactic relations in the transfer, or do we pre-annotate (e.g. with CG) then use the tags from CG to constraint the parser?
  • Can/should we do unification in the grammar (e.g. to avoid rules like SN -> adj n matching when adj.G and n.G are not the same)?
    If a language uses CG, the rule SN -> @A→ @N would only match where CG mapped @A→ (and CG can do unification with less trouble, not mapping @A→ where gender differs)
    • However, if we are to propagate attributes up the tree as well, it makes sense to have unification as well, so we can say NP[gen=X] -> D[gen=X] N[gen=X]
  • Should the transfer allow for >1 possible TL translation ? to allow 'lexical selection' inside transfer as well as outside ?
  • Can we learn transfer grammars from aligned treebanks ?

[edit] Algorithms

[edit] Usage

$ svn co https://svn.code.sf.net/p/apertium/svn/branches/transfer4

$ cd transfer4

$ cd eng-kaz

$ make
Files
  • eng-kaz.grammar: Transfer grammar file for English→Kazakh
  • eng-kaz.t1x: Categories (terminals) and attributes for English→Kazakh
Apply the transfer grammar
$ cat input/input.01.txt | ./eng-kaz.parser 
^you<prn><subj><p2><mf><sp>/сен<prn><pers><subj><p2><mf><sp>$ ^Kazakhstan<np><top><sg>/Қазақстан<np><top><nom>$ ^to<pr>/$ 
^go<vblex><past>/бар<v><iv><past>$ ^that<cnjsub>/$ ^I<prn><subj><p1><mf><sg>/Мен<prn><pers><subj><p1><mf><sg>$ 
^know<vblex><pres>/біл<v><tv><pres>$ ^.<sent>/.<sent>$ 
Print out the source tree
$ cat input/input.01.txt | ./eng-kaz.parser -s -p >/dev/null
(S (S1 (PRNS (subj_pron (^I<prn><subj><p1><mf><sg>/Мен<prn><pers><subj><p1><mf><sg>$))) 
(SV (V (pers_verb (^know<vblex><pres>/біл<v><tv><pres>$))))) (Ssub (cnjsub (^that<cnjsub>/$)) 
(S1 (PRNS (subj_pron (^you<prn><subj><p2><mf><sp>/сен<prn><pers><subj><p2><mf><sp>$))) 
(SV (V (pers_verb (^go<vblex><past>/бар<v><iv><past>$))) (SP (prep (^to<pr>/$)) 
(SN1 (SN (N (nom (^Kazakhstan<np><top><sg>/Қазақстан<np><top><nom>$))))))))) (X (sent (^.<sent>/.<sent>$))))
Print out the target tree
$ cat input/input.01.txt | ./eng-kaz.parser -p >/dev/null
(S (Ssub (S1 (PRNS (subj_pron (^you<prn><subj><p2><mf><sp>/сен<prn><pers><subj><p2><mf><sp>$))) 
(SV (SP (SN1 (SN (N (nom (^Kazakhstan<np><top><sg>/Қазақстан<np><top><nom>$))))) (prep (^to<pr>/$))) 
(V (pers_verb (^go<vblex><past>/бар<v><iv><past>$))))) (cnjsub (^that<cnjsub>/$))) 
(S1 (PRNS (subj_pron (^I<prn><subj><p1><mf><sg>/Мен<prn><pers><subj><p1><mf><sg>$))) 
(SV (V (pers_verb (^know<vblex><pres>/біл<v><tv><pres>$))))) (X (sent (^.<sent>/.<sent>$))))

[edit] References

  • Prószéky & Tihanyi (2002) "MetaMorpho: A Pattern-Based Machine Translation System"
  • White (1985) "Characteristics of the METAL machine translation system at Production Stage" (§6)
  • Slocum (1982) "The LRC Machine translation system: An application of State-of-the-Art ..." (p.18)

[edit] Further reading

[edit] See also

[edit] External links

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