Preliminary Recommendations

UPenn Treebank

This section gives a short survey of the second phase of syntactic annotation of the UPenn Treebank Project, as a summary of the publications Marcus et al. (1993) and Marcus et al. (1994).

Annotation in phase I

The first phase of the UPenn Treebank project (from November 1989 to December 1992) produced 4.5 million words of text, all tagged for part of speech and 2/3 skeletally bracketted. The text was automatically tagged and parsed (using the Fidditch partial parser), and then corrected by hand. The syntactic analysis used a modified form of the Lancaster Treebank approach, using a context-free structure.

The main goals of the second phase, which began in 1993, were the following:

Mark predicate-argument structure

-- Most importantly, the notation should allow for automatic extraction of predicate argument structure.

Provide a richer syntactic annotation

-- A broader coverage of syntactic phenomena described is aimed at. (See table of old and new syntactic labels.

Describe non-continuous structures/dependencies

-- This was formerly made difficult due to the restrictions of a context-free mechanism.

Mark grammatical functions and semantic relations

-- How are subconstituents semantically related to their predicates? At a minimal level, logical subjects and objects are to be marked.

Provide a standard objective methodology for parsers

-- Comparison of parsers that rely on deeper (i.e. closer to predicate argument structure) syntactic representation with surface parsers can be facilitated by marking of predicate argument structure.

Provide a better consistency of analyses

-- Correction of some previous inconsistencies in syntactic tagging.

Annotation in phase II

The following issues were to be addressed in phase II of the project:

• Consistent treatment of related grammatical phenomena.
• Null elements and indexing encode underlying structure.
• Discontinuous elements are marked by a non-context free mechanism.
• Clearly distinguishable semantic roles, i.e. semantic labels identifying role with respect to predicate, are marked.
• Distinction between verb arguments and adjuncts where distinctions are clear (where they are not, the notational device -CLR is used). The difference between argument and adjunct is not structurally marked.
• Gapping: recovery of predicate argument structure for whatever structure is complete within the sentence.
• Each syntactic bracket has at least one label and up to four labels (including numerical indices).

Consistency

Example: A predicate is always either

• The lowest VP; or
• The phrasal structure immediately under copular be .

  (S (NP-SBJ your safety belt)
  
     (VP is-PRD your friend))

• in `small clauses' the constituent tagged -PRD

(S (NP-SBJ I)

   (VP consider

      (S (NP-SBJ Kris)

         (NP-PRD a fool))))

Null elements

• Two kinds of null elements (cf. 4 types in UPenn 1):
  • `*T*' for WH-movement and topicalisation; and
  • `*' for all other null elements.
• Coindexing provides underlying position .
• WH-prefixed labels (WHNP, WHADVP, WHPP) only when there is WH-movement, not in WH-questions (SBARQ), not in auxiliary inverted structures (SQ).
• Predicate argument structure can be recovered by replacing a null element with coindexed lexical material: eat(Tim, what) from
• Phenomena: passives, zero subjects in infinitival constructions, object and subject control, topicalisation.

  (SBARQ (WHNP-1 What)
  
         (SQ is
  
             (NP-SBJ Tim)
  
             (VP eating
  
                 (NP *T*-1)))
  
          ?)

Some examples are shown below of the use of null elements:

• Infinitive constructions

  (S (NP-SBJ-1 Chris
  
     (VP wants
  
         (S (NP-SBJ *-1)
  
            (VP to
  
                (VP throw
  
                    (NP the ball)))))))

• Object control

  (S (NP-SBJ Ford
  
     (VP persuaded
  
         (NP-1 Zaphod
  
         (S (NP-SBJ *-1)
  
            (VP to
  
                (VP run
  
                    (PP-CLR for
  
                           (NP president)))))))))

• Subject control

  (S (NP-SBJ-1 Zaphod
  
     (VP promised
  
         (NP Ford
  
         (S (NP-SBJ *-1)
  
            (VP to
  
                (VP run
  
                    (PP-CLR for
  
                            (NP president)))))))))

• Raising

  (S (NP-SBJ-3 Everyone)
  
     (VP seems
  
        (S (NP-SBJ *-3)
  
           (VP to
  
              (VP dislike
  
                  (NP Drew Barrymore))))))

Discontinous elements

The context free mechanism of Phase I led to the trapping problem when a sentential level adverb is followed by verb complements.

With context free notation, one can do one of the following, with their respective consequences:

• Treat complement right Adverb trapped in VP

  (S (NP-SBJ Chris)
  
     (VP knew
  
         (SBAR yesterday
  
            that
  
              (S (NP-SBJ Terry)
  
                (VP would
  
                   (VP catch
  
                      (NP the ball)))))))

• Treat adverb right Complement must (falsely) attach to S

  (S (NP-SBJ Chris)
  
     (VP knew)
  
      yesterday
  
     (SBAR that
  
          (S (NP-SBJ Terry)
  
             (VP would
  
                (VP catch
  
                   (NP the ball))))))

In UPenn II, discontinuous elements are called pseudoattached:

• *ICH* Interpret constituent here (simple extraposition)
• *PPA* Permanent predictable ambiguity
• *RNR* Right node raising
• *EXP* Expletive

Simple extraposition: *ICH*

(S (NP-SBJ Chris)

   (VP knew

       (SBAR *ICH*-1)

       (NP-TMP yesterday)

       (SBAR-1 that

             (S (NP-SBJ Terry)

                (VP would

                   (VP catch

                      (NP the ball)))))))

True ambiguity: *PPA*

Even given context, the ambiguity cannot be resolved for human annotators.

• Attach at most likely site (or at higher site);
• Mark other possible sites with *PPA* element.

(S (NP-SBJ I

       (VP saw

           (NP (NP the man)

               (PP *PPA*-1)

           (PP-CLR-1 with

                     (NP the 

                         telescope))))))

Right node raising: *RNR*

The same constituent appears to have been shifted out of both conjuncts.

(S But

   (NP-SBJ-2 our outlook)

   (VP  (VP has

            (VP been

                (ADJP *RNR*-1)))

         ,

         and

         (VP continues

             (S (NP-SBJ *-2)

                (VP to

                    (VP be

                        (ADJP *RNR*-1)))))

         ,

         (ADJP-1 defensive)))

Extraposed sentences with `it'

• It is recognised as surface subject;
• Extraposed clause is attached at S level with *EXP* attach;
• Extraposed clause is interpreted as a subject of a pleasure (it ignored for argument interpretation).

(S (NP-SBJ (NP It)

           (S *EXP*-1))

   (VP is

       (NP a pleasure))

   (S-1 (NP-SBJ *)

        (VP to

            (VP teach

                (NP her)))))



pleasure(teach(*someone*, her))

Semantic roles/grammatical functions

As it is very difficult to determine a set of underlying semantic roles, the UPenn II Project restricted itself to the clearly distinguishable semantic roles listed below. The given list mostly relates to adjuncts.

Semantic roles

• -VOC vocatives
• -DIR direction, trajectory
• -LOC location
• -MNR manner
• -PRP purpose
• -TMP temporal phrases
• -BNF benefactive
• -EXT extent

Grammatical Functions

• -SBJ surface subject
• -LGS logical subjects in passives
• -- obvious NP and S objects
• -ADV clausal and NP adverbials
• -DTV dative object (unshifted form)
• -NOM non-NPs acting as NPs
• -PRD non VP predicates
• -CLF true clefts
• -TPC topicalised and fronted constituents
• -PUT locative complement of put
• -CLR special class `closely related'

The special class `closely related' is used for constructions occupying middle ground between arguments and adjuncts. These constructions correspond to Quirk et al.'s class of predication adjuncts, some phrasal verbs (Quirk et al., 1985). Usage:

• On S or SBAR: semicomplement clauses with use, design, hire, build, cost, take and it-extraposition.

  (S (NP-SBJ the process)
  
     (VP will
  
         (VP take
  
             (NP (QP as many as six)
  
                  months)
  
             (S-CLR (NP-SUBJ *)
  
                    (VP to
  
                        (VP complete))))))

• On PP, ADVP, SBAR-PRP: categories normally interpreted as adverbials (adjuncts), -CLR indicates a closer relationship.

  (VP associate
  
      (NP snow)
  
      (PP-CLR with
  
            (NP winter)))

• On NPs: fixed phrases like take place.

  (VP taking
  
      (NP-CLR care)
  
      (PP-CLR of
  
          (NP the problem)))

Examples are given below for the tags -DTV, -PRD, -TPC, -CLF and -PRP:

-DTV

(S (NP-SBJ Aristotle)

   (VP gave

       (NP the book)   

       (PP-DTV to

               (NP Plato))))







(S (NP-SBJ Aristotle)

   (VP gave

       (NP Plato)

       (NP the book)))

-PRD

Non-VP predicates

(SQ Was

    (NP-SBJ he)

    (ADVP-TMP ever)

    (ADJP-PRD successful)

    ?)





(SINV and

     (ADVP-PRD-TPC-1 so)

     (VP did

         (ADVP-PRD *T*-1))

     (NP-SBJ the hippopotamuses))

-TPC

(S (PP-TPC-12 Of

        (NP (NP the 500 barbers)

                (PP-LOC in

                    (NP Philadelphia))))

   ,

   (NP-SBJ (NP (QP only 10))

           (PP *T*-12))

   (VP know

       (SBAR (WHNP-13 what)

             (S (NP-SBJ they)

                (VP are

                    (VP doing

                        (NP *T*-13)))))))

-CLF

(S-CLF (PP-TMP In

               (NP the past))

       ,

       (NP-SBJ it)

       (VP has

           (VP been

               (NP-PRD-2 the

                         husband)

                   (SBAR (WHNP-1 who)

                         (S (NP-SBJ *T*-1)

                            (VP has

                               (VP been

                                  ADJP-PRD-3

                                    dominant)))))))

-PRP

(S (NP-SBJ-1 (NP activity)

             (PP-LOC at

                   (NP (NP a number)

                       (PP of

                           (NP brokerage

                               houses)))))

    (VP was

        (VP curtailed

            (NP *-1)

            (PP-PRP as

               (NP (NP a result)

                   (PP of

                     (NP the earthquake))))))

Gapping

• The extraction of predicate-argument structure for gapped sentences is possible if the full parallel structure is within the same clause.
• The parallel structure is then used as a template: arguments (e.g. NP-SBJ=1) are mapped from gapped clause onto the template (e.g. NP-SBJ-1).
• Constituent NP=1 should be mapped over NP-1 in the largest conjoined structure that NP-1 and NP=1 both occur in.

(S (S (NP-SBJ-1 Mary)

      (VP likes

          (NP-2 Bach)))

   and

   (S (NP-SBJ=1 Susan)

      ,

      (NP=2 Beethoven)))



like(Mary, Bach)

like(Susan, Beethoven)

(S (S (NP-SBJ I)

      (VP eat

          (NP-1 breakfast

          (PP-TMP-2 in

               (NP the morning))))

   and

   (S (NP=1 lunch)

      (PP-TMP=2 in

            (NP the afternoon)))))

However, there is no recovery of structure outside the single sentence concerned.

Who threw the ball?



(FRAG (NP Chris)

      ,

      (NP-TMP yesterday))



What is Tim eating?



(FRAG (NP-SBJ Mary Ann)

      (VP thinks

          (SBAR 0

                (FRAG (NP chocolate)))))