Prologue

ICONS might be a useful tool towards the under-specification of modifier attachment.

This argument position in this modifier can be x, y, or z but not w.

Is this overloading? Not in the sense of what the ICONS formalism can do. It's just about being able to say any two indices stand in a relation to each other. If the representation can be done that way, don't see a formal problem. But disjunction is not true underspecification. Possibly need access to character positions to truly underspecify.

Possible technical difficulty: modifiers need the label too. But can't we get the label from the index, because it's the label of the EP that has that index as the ARG0? This would require a special icons constraint that applies to modifier attachment (and not to say anaphora resolution). It also means that the ICONS have to be looked at (for these constraints) in the process of computing fully scoped forms.

In terms of DMRS the necessary correlation between the label and the coindexation works because there is just one link there, and it's natural to underspecify those links. Have access to the topological properties of the links (for avoiding crossing).

Other possible applications of ICONS: appositives, non-restrictive relative clauses, parentheticals. Come back to those.

The big question

Is modifier attachment underspecification the right thing to do?

Pros/Motivation [summarized at end of the session]:

Currently being forced to say more than the context tells us. Conventional syntax does seem to want to say something about these ambiguities. But we shouldn't mistake conventional syntax for deep truth. Does the conventional representation of constituent structure for PP attachment buy us anything in terms of well-formedness. (Distinct from cases where the structure makes thing unambiguous, e.g., PP inside a topicalized NP.)

Cons/challenges [summarized at end of session]:

The more detailed discussion

With compound noun attachment, there are examples where arguably the stress is different based on the bracketing. Possible example: interaction of stress with focus projection. But we're hoping to do that off the MRS only anyway.

High attachment of on to e1 makes inaccessible the low attachment of second PP. => Attachment resolution will be like scope resolution: will require that we create internally consistent representations.

Currently get 5 parses of that example. Proposal is to have just one structure, with an underspecified or otherwise compact representation of the 5 attachments. Do we need to encode the dependency between the two in the result of parsing? What information does the modifier attachment resolution procedure need in order to do that?

Non-projectivity: in can only attach to astronomer if on isn't linked to saw --- otherwise it would cross the dependency.

True underspecification: special links that are equivalent to a low-branching syntax. Give the minimal one only? Maximal one too? Space of possible candidates is not enumerated anywhere during parsing. Resolution procedure knows to treat them separately. Need to make rules for how to project there, with the goal of doing this based only on semantics (MRS w/ICONS) plus linear order in the surface tree.

We do get non-projectivity in some cases. How do such cases interact with modifiers?

That's a crossing dependency --- unless we treat it as a co-reference link rather than a syntactic link (which we want to do independent of this underspecification).

Plug for multilingual investigation: look at German (non-projectivity) and Japanese (head-final order).

(Non-)projectivity arises in DMRS because of the algebra. Semantic head supplies the slot, filled with the hook of the non-head. When you have external arguments or take the slots from the non-head daughter further up that leads to non-projectivity. Dick Hudson paper on no-tangling constraint on his dependency structures: all of his examples are cases where we pass up an external argument. Simple ex (not from Hudson): Kim believes Sandy must sleep. Want sleep taking Sandy and believe taking sleep.

Are there configurations cross-linguistically where there would be non-projectivity on modifier predicate-argument links? More specifically could be that the resolved links can't cross another intersective modifier. Some links may be crossable.

Scopal modifiers?

In German, there is more ambiguity with scopal modfiers, e.g., [ scopal adverb V scopal adverb ]. Intersective and scopal modifiers scramble freely.

EB proposes that if we are going to do this only for intersective modifiers and not scopal ones, need a principled reason for that. In DMRS the scopal ones are also just links, so could possibly also be underspecified. (Could that be mocked up in the ICONS account?)

Dan is optimistic that the attach low analysis can be built in the grammar (without help from the parsing engine).

The current ERG has relative clause extraposition, but not yet extended to PP extraposition because the frequency of the construction does not merit the cost.

Could be that there is a certain kinds of cases where non-projectivity is allowed in the linking of modifiers. Can we identify these on the basis of MRS + surface order alone?

Alternatively, if that isn't feasible, could say that there are two kinds of modifier attachment syntactically in English: the ordinary one that we are now underspecifying, and extraposition. This would lead to some residual ambiguity in some (many?) cases. (And then these end up as another case of close paraphrases that don't quite have parallel MRSs.)

Dan hopes to not use extraction and rather attach as low as possible, which is actually high : S attachment. (Alternative: extract only low.) Can we give a single attachment point to the highest verb and figure out that there would be other candidates down inside the clause:

Only the verbs: Ross 1968 CPNC. So the rightward-down search has to know that it's looking for verbs only (manager and appointment are not possible attachment sites.)

[Cross-linguistic considerations: is CPNC a universal? What about cases where we get the stacked PPs to the left without extraction? How language specific are the constraints on resolution?]

To keep the resolution procedure from being language-specific, use different types of links to trigger different types of interpretation procedures. Then the grammars for different languages can specify different kinds of links.

NNNN compounds: build one unique syntactic structure. Relatively simple case. What about adjectives inside of NN compounds: attaches to its nearest host (noun to its right: I'm this kind of modifier, here's what you do to interpret me: fluffy towel rack has one syntactic structure but two interpretations, one of which is too 1970s to contemplate. the IBM quarterly shareholder report: Two different kinds of links: one for noun compound structures which impose one kind of resolution behavior and one for adjectives that something different.

Syntax tree gives (when we're done with parsing what we have is): an attachment site, the link type, and constraints on the type of the ARG1 of the modifier.

Do we need to think of any islands, things that block rightmost modifiers from going up further? One example might be subordinate clauses. Candidate generalization: no intersective modifiers of a clause after clausal modifiers of that clause.

How do we do annotation of this (to the extent possible)?

Related: How we represent the structure? Could enumerate, but that would be impractical. One options is some sort of disjunctive forms for attachment of each modifier, with constraints (dependencies between choices for) on the combination of modifiers. XLE has one solution to this: context representation for disjunctions: representing disjunction as conjunctive form of implications. Another solution is "named disjunction" or "distributed disjunction". "contexted disjunctions" (Maxwell and Kaplan 199X).

Minimal set of extra predicates to model the satisfiability of the entire semantics. XLE offers a packed representation within the FSs. If you pick one disjunct, the corresponding impossible choices (disjuncts) disappear. Like discriminant-based treebanking? Not exactly: folks in Bergen looked at this functionality in the XLE and decided to use discriminant-based approach instead.

If we characterize modifier attachment as semantic rather than syntactic ambiguity, and if we want annotators to disambiguate (or partially do this), then treebanking would be a two-stage process: choose the tree first then do the semantic resolution (maybe interleaved, if we get clever).

Not saying (like we did with scope): We moved this out of the syntax, so it's not our problem.

Scope resolution by hand is impractical, partially because so many of the scopes are equivalent. Koller/Thater work on collapsing those might pull out enough that the problem becomes, if not tractable, at least possible to look at. Treebanking scheme where annotators are presented with scopes created through heuristics and asked right or wrong? (Would have to have Aurelie's work on underspecified quantifiers fed in first, because the presence of an ambiguity depends on the interpretation of the unspec_q_rel.)

In what application contexts do we want to resolve the modifier attachment? In MT in some cases, maybe don't need to. In relation extraction or QA, could possibly absorb some vagueness, but don't want complete underspecification. So automatic resolution would be a practical necessity: motivation for treebanking. Automated disambiguation would also be two-stage (or joint modeling over different structures).

Doing things in terms of MRS and WordNet features are different kinds of semantic features. Many have found that neither has been very successful in helping with parse selection. Just MRS structure only slightly worse than syntax only.

Woodley did an error analysis of parse selection last year. Coordinate structures and PP attachment were high on the list. Copestake et al at JHU workshop got a significant difference on coordinate structures for CCG parser using distributional features.

Proper evaluation of this would require a treebank without artificial heuristics like "when in doubt attach low". That might bias things towards syntactic features. Feature choice (in ML systems) is a matter of recreating the heuristics, rather than the linguistic knowledge, in the annotations.

In the current discriminant-based set up, finding a non-singleton subset of trees is not a well-defined, so Redwoods project reverted to full disambiguation (even where heuristics are required). Can't carve the space of trees into arbitrary subsets and not the subsets we wanted. Might be possible to get to the subsets we're interested in in the proposed 2nd stage.

Would be an interesting dataset for studying modifier attachment (incl. NNNN compound structure; not coordination though --- that wouldn't fall under this analysis). Replacing Ratnaparki dataset (from PTB, constrained task) and one other small hand-crafted set.

Should make this move only with careful consideration: moving something out of the syntax into the semantics:

Possible evidence that PP attachment is (at least partially) a syntactic ambiguity:

MSc student (at UiO) working on measuring affinity of predicates for each other over the Google 1T corpus. "V pron P" would favor high attachment. (Extension of B&K work on PTB Sec 23 parsing to ERG/Redwoods.) This is giving strong improvement in exact-match accuracy. The features are defined in terms of head words, which define to more than unary constructions in the grammar, and it helps to label the features with the construction names from the grammar. Many of these are modifier attachment decisions. The proposed move would replace ~2 doz syntactic head-modifier constructions with one structure (ARG1) in the semantics. Not broken down by type of constructions (in the analysis) --- need to know how much of the help is actually in other structures rather than head-modifier (coordination, etc). Also: once again the heuristics that were applied to get one tree (somewhat artificially) might be partially behind this result as well.

=> deciding whether modifier attachment is fundamentally syntactic should include looking at both competence and performance (e.g., parse selection)

We're talking about "procedures", but need to maintain reversibility.

We keep talking in terms of trees and such; need to translate into semantic notions. The set of constraints that syntax currently encodes for us, we need to transfer to the semantic level so that we can obey them in the semantic resolution. Or maybe find constraints in the semantics that will do the work for us.

The syntax is there because people have semantic intuitions about these attachments, and used syntax to express them. No evidence yet that there's anything in the syntax that actually depends on this.

Could alternatively say there's a set of semantic constraints on the resolution that are only partially guided by the syntax, and can be worked with independent of the syntax except where the syntax directly guides the semantics.

To disambiguate, what properties do we want to be accessible? Do we want to do the levels separately or jointly (using some projection set up where there are links between syntax and semantics that the analysis selection engine can take advantage of).

If we allow ourselves the two stage process, we allow ourselves the choice of putting things or there. Currently we have:

Various ad hoc attempts to disambiguate (as separate stages):

This move is introducing a new type of ambiguity from the above. We're already multi-stage, but this is a new stage.

Another place where we could hope for another division of labor: apposition and coordination:

Would be nice to build one single structure that is underspecified between apposition and coordination. But those are two different things, so an entertaining puzzle.

If some relative clauses are anaphoric in nature, not attaching them the same way. Extraposed ones are attached differently.

Relative clause whose modifier argument is not bound to anything. RASP attaches in fewer and uses a separate anaphora resolution algorithm to handle it.

More general point: There are other places where you can get readings that are both pragmatically plausible as compared to the vast majority of ambiguities where the non-selected parses a human would never want (and human processors might not come up with). Treebankers have different kinds of decisions to make: some cases are clearly just silly trees, in others, the meaning of the sentence has to be taken into consideration.

Point here is that it's another place where people are coerced into making decisions they are not informed to make. It would be nice to be able to underspecify the forest in this case here.

Church & ? paper noting that this is a catalan series had an underspecification account.

Non-projectivity isn't always the same between syntactic and semantic dependencies because of semantically empty things.

Proposal to reconsider not completely disambiguating profiles in treebanking.

Skepticism about inter-annotator agreement on when to stop. Replace heuristics for what to do when you don't know with heuristics for where to stop. Worry that differences in world knowledge might lead to (additional) variability in annotation. The to one tree version is possibly artificially simple in this way.

Try a small scale experiment, trying to measure IAA on this additional choice point.

Yi's experience with WSJ texts: some residual ambiguity left in early stages. Compound nouns, quotatives (before Dan had them worked out well), ...

In the experiment allow knocking out individual trees as a last resort to see whether the cases that caused the turn around before are coming up. Sounds like the current tool might allow us to carry out the experiment without further software development. => Paper (e.g., LAW) on whether the stopping can be done consistently across annotators.

PPs modifying PPs, because of

But it also happens with resultative PP complements (which aren't just modifiers in the semantics):

Could search in the current Treebanks --- in Fangorn to answer this question. Homework: Try it!

Update 13-jun:

Fangorn URL (possibly temporary): http://hum.csse.unimelb.edu.au:9090

Sample searches:

(As far as I know, there isn't yet a wild card that would let us search over P_NP_I*, nor a version of the LOGON data loaded that has abbreviations for node labels, though that should be possible in principle.)

WeSearch/UnderspecifedAttachment (last edited 2018-06-19 14:20:08 by EmilyBender)

(The DELPH-IN infrastructure is hosted at the University of Oslo)