Tuesday, February 9, 2010

What else is wrong with the trees?

I've already explained why I don't like using trees as an intermediate parser representation. Here's why I don't want to use them as the final parser representation, i.e. for capturing the syntactic structure of a text.

1. Double attachment

I wrote a letter to my friend. Did I write something (a letter) to my friend or was it the letter to my friend that I wrote? I have no idea. Both alternatives seem plausible to me. So why should I make some unmotivated choice if I can have 'to my friend' attached to both 'wrote' and 'letter'? But the result won't be a tree.

2. Overlapping

zum means zu (preposition) + dem (dative definite article). If the tree has separate slots for prepositions and articles (e.g. PP and DP heads), this word would go to both, which is not tree-like.

Welsh has single constituent subject-verb agreement. For example, in the Welsh translation of (very "natural") I and my brother saw ourselves, saw agrees with singular I, whilst ourselves agrees with the plural compound I and my brother. If we think that the agreed items should be directly connected in the syntactic structure (not necessarily true, but would be nice), then saw should be directly connected both with I (agreement) and I and my brother (subject).

However, Doctor, I'll stay here. IMHO any text should be analyzed as is. In particular, the punctuation should be processed in the same way as the words, since it's part of the text and is subject to grammatical rules of the language called Written English. But however at the beginning of a clause requires a comma after itself. The title of the Doctor being addressed, also requires to be surrounded by commas. So, where does the comma between however and Doctor belong? If you ask me, it belongs to both places, and this again isn't tree-like.

3. Discontinuous constituents

Actually, there's nothing wrong about them from programmer's perspective. But both the phrase-structure and dependency grammars prohibit discontinuous constituents. They don't allow the lines connecting their nodes to cross for some theoretical reasons.

So, for me trees are also not very convincing as the 'ideal' syntactic representation. But is there an alternative? Yes, and not a single one. Attribute-value matrices, for example. Or constructions. But that's another story.


Muhammad Alzaidi said...

Hi Peter,

I understand your argument against trees.As a student (beginner)in linguistics in general and in syntax in particular (-;),I think trees are working and a good source of representing a structure.. you mentioned in your last papragraph what alternatives are.. and you mention ( Attribute-value matrices) in fact, more investigations reveals that trees sometimes help for example Attribute-value matrices, as far as I know, does not provide us with the linear order... for example if we look at 'and' as a conjunction from pragmatics perspective we can find that at least in Arabic it sometimes implies order of events for example:
{[A] and [B]}
which is not as same as {[B] and [A]}
in this structure, A as an event precedes B's event so Attribute-value matrices seems to me that it fails to account for the order. As a result of that trees along with Attribute-value matrices can provide an accurate and explanatory explanation.For example within LFG we can link the c-structure with f-structure via a correspondance function and we provide an account for the linear or (precedence).in fact what I have said is not new it has been pointed out for example there is one called Peter (a student in syntax) who did a brilliant work on Agreement in Arabic and he visited our department and Louisa invites us mentions this sort of problem within Attribute-value matrices.

Peter Gromov said...


AVMs is only a means, it can be used however you like. In particular, representing the word order isn't a problem with them. You just have lists of AVM as attribute values, and lists are ordered. HPSG has been using that for a long time. So trees are not the only ones to rescue here. And they have the disadvantages I've listed. Anyway, I'm into constructions, though the more I think of them, the more they resemble HPSG's AVM's.