Treatment of Long Distance Dependencies in LFG and TAG: Functional Uncertainty in LFG Is a Corollary in TAG

TREATMENT OF LONG DISTANCE DEPENDENCIES IN LFG AND TAG: FUNCTIONAL UNCERTAINTY IN LFG IS A COROLLARY IN TAG" Aravind K. Joshi Dept. of Computer & Information Science University of Pennsylvania Philadelphia, PA 19104 joshi@linc.cis.upenn.edu K. Vijay-Shanker Dept. of Computer & Information Science University of Delaware Newark, DE 19716 vijay@udel.edu ABSTRACT In this paper the functional uncertainty machin- ery in LFG is compared with the treatment of long distance dependencies in TAG. It is shown that the functional uncertainty machinery is redundant in TAG, i.e., what functional uncertainty accom- plishes for LFG follows f~om the TAG formalism itself and some aspects of the linguistic theory in- stantiated in TAG. It is also shown that the anal- yses provided by the functional uncertainty ma- chinery can be obtained without requiring power beyond mildly context-sensitive grammars. Some linguistic and computational aspects of these re- sults have been briefly discussed also. 1 INTRODUCTION The so-called long distance dependencies are char- acterized in Lexical Functional Grammars (LFG) by the use of the formal device of functional un- certainty, as defined by Kaplan and Zaenan [3] and Kaplan and Maxwell [2]. In this paper, we relate this characterization to that provided by Tree ~,djoining Grammars (TAG), showing a di- rect correspondence between the functional uncer- tainty equations in LFG analyses and the elemen- tary trees in TAGs that give analyses for "long dis- tance" dependencies. We show that the functional uncertainty machinery is redundant in TAG, i.e., what functional uncertainty accomplishes for LFG follows from the TAG formalism itself and some fundamental aspects of the linguistic theory in- stantiated in TAG. We thus show that these anal- yses can be obtained without requiring power be- yond mildly context-sensitive grammars. We also *This work was partially supported (for the first au- thor) by the DRRPA grant N00014-85-K0018, AltO grant DAA29-84-9-0027, and NSF grant IRI84-10413-A02. The first author also benefited from some discussion with Mark Johnson and Ron Kaplan at the Titisee Workshop on Uni- fication Grammars, March, 1988. briefly discuss the linguistic and computational significance of these results. Long distance phenomena are associated with the so-called movement. The following examples, 1. Mary Henry telephoned. 2. Mary Bill said that Henry telephoned. 3. Mary John claimed that Bill said that Henry telephoned. illustrate the long distance dependencies due to topicalization, where the verb telephoned and its object Mary can be arbitrarily apart. It is diffi- cult to state generalizations about these phenom- ena if one relies entirely on the surface structure (as defined in CFG based frameworks) since these phenomena cannot be localized at this level. Ka- plan and Zaenan [3] note that, in LFG, rather than stating the generalizations on the c-structure, they must be stated on f-structures, since long distance dependencies are predicate argument dependen- cies, and such functional dependencies are rep- resented in the f-structures. Thus, as stated in [2, 3], in the sentences (1), (2), and (3) above, the dependencies are captured by the equations (in the LFG notation 1) by 1" TOPIC =T …

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