{ "paper_id": "C88-1013", "header": { "generated_with": "S2ORC 1.0.0", "date_generated": "2023-01-19T12:15:39.275331Z" }, "title": "", "authors": [], "year": "", "venue": null, "identifiers": {}, "abstract": "", "pdf_parse": { "paper_id": "C88-1013", "_pdf_hash": "", "abstract": [], "body_text": [ { "text": "The corresponderlce between a string of a language and its abstract representation, usually a (decorated) tree, is not Straightforward.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "AB~AC E", "sec_num": null }, { "text": "Ilowever, it is desirable to maintain it, for Example to build structured editors for tex ts wr 1 t t El/ i n nat urn 1 Ianguage. AS such ccr'resp)ndences must be compos 1 t iona] , we ca ] I ~hem \"Structured Strmg--lree Correspondences\" (SSTC).", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "AB~AC E", "sec_num": null }, { "text": "We ~jrgue that a SSTC is m fact composed of two mterrelated correspondences, one between nodes and substr ings, and the other between subt tees and substrings, the substrings being possibly discontinuous in both cases.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "AB~AC E", "sec_num": null }, { "text": "We then proceed to show how to define a SSTC witl~ a Structura! Correspondence Static Grammar (SCSG), and ~qich constraints to put on the rules of the SCSG to get a \"natural\" SSTC.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "AB~AC E", "sec_num": null }, { "text": "linguist ic dascr lpt ors, distort inuous consti tuents, discont imuous phrase structure grammars, st rLICt ured str ing-tree correspondences, structural corrosp:)ndence static gralilnlars t~t~),&~D~:", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Kev~d'~ :", "sec_num": null }, { "text": "DPSG, M], N[., SSIC, STCG.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Kev~d'~ :", "sec_num": null }, { "text": "Ordered trees, annotated with simple labels or COmplex 'cecora~ions\" (property lists), are widely used for representing natural language (NL) utterances. This oErresponOs to a hierarchical view: the utterance is decomposed into groups and subgroups. When the depth of lmguiscic analys~s is suc~ that a representation m terms of graphs, networks or sets of formulas would l)e more Jirect, one often st i ] I prefers to use tree structures, at the price of encoding the desired informa::ion in the decorations (e g., by \"ooindexing\" two or more nodes). This is because trees are conceptual]y and a]gorithmical]y eas~er to manipu]ate, and also because all usua] interpretations based on the linguistic structure are more or less \"compositiona]\" in nature.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "~U.\u00a23JLQ_N", "sec_num": null }, { "text": "Grammar, or by a (projective) Dependency Grammar, the tree structure \"contains\" the associated string in some easily defined sense. ]n particular, the surface order of tile string is derived from some ordered traverse1 of the tree (left--to-right order of the leaves of a constituent tree, or infix order' foe a dependency tree).", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "If a language is described by a classical Phrase Structure", "sec_num": null }, { "text": "However, if one wants to associate \"natural\" structures to strings, for examole abstract trees for programs or predicate-argument structures for NL utterances, this is no longer true. Elements of the string may have been erased, or duplicated, some \"discontinuous\" groups may have been put together, and the surface order may not be reflected in the tree (e.g., for' e normalized representation).", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "If a language is described by a classical Phrase Structure", "sec_num": null }, { "text": "Such correspondences must be compositional: the complete tree corresponds to the complete string, thee subtrees correspond to suPstrings, etc. Hence, we call them \"Structured String-tree Correspondences\" (SSTC).", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "If a language is described by a classical Phrase Structure", "sec_num": null }, { "text": "For some applications, like classical (batch) Machine Translation (MT), it is not necessary to Keep the correspondence explicit:", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "If a language is described by a classical Phrase Structure", "sec_num": null }, { "text": "'For revising a translation, it is enough to show the correspondence between two sentences or two paragraphs.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "If a language is described by a classical Phrase Structure", "sec_num": null }, { "text": "14owever, if one wants to build structured editors for texts written tn natural language, thereby using at the same time a string (the text) and a tree (its representation), it seems necessary to represent explicitly the associated SSTC.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "If a language is described by a classical Phrase Structure", "sec_num": null }, { "text": "In the first part, we briefly review the types of string-tree correspondences whloh are implied by the most usual types of tree representations of NL utterances.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "If a language is described by a classical Phrase Structure", "sec_num": null }, { "text": "We argue that a SSTC should in fact be composed of two interrelated correspondences, one between nodes and substrings, and the other between subtrees and substrings, the substrings being possibly discontinous m both cases. This is presented in more detail in the second part.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "If a language is described by a classical Phrase Structure", "sec_num": null }, { "text": "]n the last part, we show how to define a SSTC with a Structural Correspondence Static Grammar (SCSG), and which constraints to put on the rules of the SCSG to get a \"natural\" SSTC.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "If a language is described by a classical Phrase Structure", "sec_num": null }, { "text": "A STRIN~ 1. p~F~E ~TRUCTURE TREES (C-STRUCTURESI Classical Phrase Structure trees give rise to a very simple Kind of SSTC. To each string w = al...an, let us associate the set of interva]s i j, O~i~j~n. w(i j} denotes the substring ai...a3 of w if iO}, and propose the two i:rees (14) and (15) below for the string \"a a v b b c c\" (also written a. 1 a.2 v b. 1 b.2 e.l c.2 to sl~L}w the positions) as more \"natural\" representations than i:he syntactic tree derived from a context-sensitive grammar in normal form for this language (all rules are of the form \"1A r --~ 1 u r\", 1 and r being the left and right ~:ontext, respectively). On certain nodes, we have represented the sequence corresponding to the complete 8ubtree rooted at the node, fel ]owed by the sequence Corresponding to the node itself.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "P_RED OATE-ARGUMENT TREES (P-STRUCTURES)", "sec_num": "3." }, { "text": "For nodes A, B, C in tree (14), this \"local\" 8equanoe ts empty.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "P_RED OATE-ARGUMENT TREES (P-STRUCTURES)", "sec_num": "3." }, { "text": "In both trees, tt i8 clear that the sequence al V bl ol corresponds to an \"incomplete\" subtree, namely V(A(al),B(bl),C(cl)) In (14) and V(al,bl,cl) in (15).", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "P_RED OATE-ARGUMENT TREES (P-STRUCTURES)", "sec_num": "3." }, { "text": "In tree 14, the cOOrdination is shoal directly on the graph, and the verb (V) is not shown as elided. ]t is a matter of further analysis to accept or not the distributive Interpretation (\"respectively\" may hold between the three groups, the last two ones, or nones).", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "P_RED OATE-ARGUMENT TREES (P-STRUCTURES)", "sec_num": "3." }, { "text": "On the contrary, tree (15), in a sense, is a more \"abstract\"", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "P_RED OATE-ARGUMENT TREES (P-STRUCTURES)", "sec_num": "3." }, { "text": "representation. It shows directly the interpretation as a coordination of two sentences, and \"restores\" the elided V.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "P_RED OATE-ARGUMENT TREES (P-STRUCTURES)", "sec_num": "3." }, { "text": "Multilevel tree structures, or m-structures for short, have been introduced by B.VAUQUOIS in 19.//4 (see (Vaupuols */8)) for the purposes of Machine Translation.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "4, MULTILEVEL TREES (M-STRUCTURES)", "sec_num": null }, { "text": "On the same graph, three \"levels of interpretation\" are described (constituents, syntactic dependencies, logical and semantic relations).", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "4, MULTILEVEL TREES (M-STRUCTURES)", "sec_num": null }, { "text": "AS seen in other examples above, the nodes ~\u00a2nich refer directly to the string do not contatn elements of the string, but rather representatives of (sequences of) elements of the string, called \"lexical units\" (LU), like \"repair\" for \"reparation\", plus some information about the derivation used.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "4, MULTILEVEL TREES (M-STRUCTURES)", "sec_num": null }, { "text": "The graph is deduced by simple rules from a dependency tree: each tnternat node t8 \"lowered\" tn the \"'\" position and its syntactic function becomes \"GOV\" (for \"governor\", or head in some other terminology), discontinuous lexical elements (like \"ne...pas\" or \"al...denn~\" are represented by one node, coordination ts represented by \"vertical ltsts\" as tn tree 14, lextoal units of referred element~ are put In the nodes corresponding to the pronouns, an approximation of colndexlng, etc.. ", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "4, MULTILEVEL TREES (M-STRUCTURES)", "sec_num": null }, { "text": "A PROPOSAL: STRUCTURED STRING-TREE CORRESPONDENCES Our proposal Is now almost complete.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "II.", "sec_num": null }, { "text": "a) The correspOndence between a string and its representation tree ts made of two interrelated correspondences: between nodes and (possibly discontinuous) 8ubstrings; between (possibly Incomplete) subtrees and (possibly dtsconttnous) substrlngs. gl b) It can be encoded on the tree by attaching to each node N two sequences of intervals, called SNODE(N) and SIREE(N), such that:", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "I. DEFINITIONS", "sec_num": null }, { "text": "1. SNODE(N) ~ STREE(N), v~ich means that SNODE(N) 18 \"contained\" tm STREE(N) with respect to tts basic elements (the w(i j}), that is, that StREE(N) = STREE(N) g SNODE(N). Note that equality can not be required, even on the leaves, because the string \"( b )\" may well have a representation tree with the unique nede b.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "I. DEFINITIONS", "sec_num": null }, { "text": "2. if N has m daughters Nt...Nm, then STREE(N) ~ STREE(N1)+...+STREE(Nm) + SNODE(N). ]n case of strict containment, the difference correspond to the elements of the string which are represented by the subtree but which are not explicitly represented, like \"(l' and \")\" in \"( b )\".", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "I. DEFINITIONS", "sec_num": null }, { "text": "c) The sequence SSUBT(X,N) corresponding to a given mcomplete subtree X rooted at node N of the whole tree T is defined recursively by: SSUB1(X,N) : STREE(X) if X : N, that is, if \u00d7 iS reduced to one node, not necessarily a leaf of T;", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "I. DEFINITIONS", "sec_num": null }, { "text": "SSUBT(X,N) = SSUBT(XI)*..I+SSUBT(XD) U SNODE(N). if N, the root of X, has p subtrees XI...XD in T.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "I. DEFINITIONS", "sec_num": null }, { "text": "In other words, one takes the smallest sequence contaming the bi9gest sequence corresponding to the leaves of x (S]REE on the leaves) and compatible with the monotony rules above.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "I. DEFINITIONS", "sec_num": null }, { "text": "Here are some interesting properties of SSTCs which may help to classify them. A SSTC is of the g~ if SNODE(N) is empty for each non terminal node N.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "I. DEFINITIONS", "sec_num": null }, { "text": "In the examples above, we have encoded the correspondence in the tree. However, this is in practice not always necessary, or even practical.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "~_R~PRE~SNTATION", "sec_num": "3." }, { "text": "in the case of explicit and projective SSTCs, for instance, the string can De obtained directly from the tree, and there is no need to show the intervals, Note that, in the process of generating a string from a tree, one naturally starts from the top, not knowing the final length of the string, and goes down recurs ]rely, dividing this i nt erv~a ] into smaller intervals.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "~_R~PRE~SNTATION", "sec_num": "3." }, { "text": "Rather than to introduce variables representing the extremities of the created intervals, it may be more practical to start from a fixed interval, say 0_1 or 0 lO0. Yhen. the Positions between the elements of G2 the string will be denoted by am increasing sequence of rational numbers (0, 1/3, 1/2, 5/?), etc.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "~_R~PRE~SNTATION", "sec_num": "3." }, { "text": "In the case of \"local\" non-projectivtty, we have tried some devices using two relative integers (POS,LEV) associated with each node N. POS(N) st~ws the relative order in the subtree rooted at mother(N), if LEV(N)=O, or more generally at tts LEV(N\u00f7I) ancestor, if t.EV(N)>O. Unfortunately, all these schemes seem to work only for particular situations.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "~_R~PRE~SNTATION", "sec_num": "3." }, { "text": "Also, if the SSTC is overlapping, or' not complete, 1( may be computationally costly fo find the (sma]lest) subtree associated with a given (possib]y discontinuous) substrtng. But this operation would be essential in a \"structural\" editor of NL texts. A possibility is then to encode the correspondence both in the tree and in the string.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "~_R~PRE~SNTATION", "sec_num": "3." }, { "text": "Finally, take the example of tree (15) above. Suppose that the user of a NL editor wants to cllange bl (Paul, in the corresponding NL example) in a way v~Hch may contradict some agreement constraint between al, v, bl and el. One should be able to ftmd the smallest SSIC containing al and other elements, that is, the subtr'ee V(al,bl,cl) and the discontinuous substring al v bl cl (the notation a..v.b..c., might be suitable, if one wants to avoid indices).", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "~_R~PRE~SNTATION", "sec_num": "3." }, { "text": "For these reasons, it may be werth~qile to COnSider the possibility of representing the $gTC independently of beth the tree and the string. This is actually the ldea behind the formalism of gTCG (String-Tree Correspondence Grammar).", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "~_R~PRE~SNTATION", "sec_num": "3." }, { "text": "The static grammars of (Vauquols & Chappuy 85) are devices to define string-tree correspondences. They have been formalized by the STCGs of (Zahartn 86).", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "~_R~PRE~SNTATION", "sec_num": "3." }, { "text": "Here, a context-free ltke apparatus of rules (also called \"boards\", for \"planches\" in French, because they are usually written with two~dtmenslonal tree diagrah~s) is used to construct the set of \"legal\" SSYCs.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "~_R~PRE~SNTATION", "sec_num": "3." }, { "text": "The axioms are all pairs (X,Y($F)), where X is an unbounded string variable, Y a starting node (standing for SENTENCE, or TITLE, for example), and SF is an unbounded forest variable.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "~_R~PRE~SNTATION", "sec_num": "3." }, { "text": "The terminals are all pairs (x,x'), where x is an element of a strtng and x' a one-node tree vZ~ich represents it.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "~_R~PRE~SNTATION", "sec_num": "3." }, { "text": "The rules chow how a SSTC t8 made up of smaller' ones. ]he generated language ts the set of all variable-free (,) pairs derivable from an axiom by the grammar rules.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "~_R~PRE~SNTATION", "sec_num": "3." }, { "text": "In order to avoid undue formalism, let us give an example for the formal language (an bn cn I n>O). Actually, the formalism is a bit more precise and powerful, because it is posslb]e to express that a correspondence in the r.h.s. (right hand side) is obtained only by certain rules, and to restrict the possible unifications (rather, a sparta1 Ktnd called \"identifications\" in (Zaharim 86}).", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "~_R~PRE~SNTATION", "sec_num": "3." }, { "text": "1'0 illustrate this, we may rewrite the last element of the r.h.s, as: .............................................................................. ", "cite_spans": [ { "start": 71, "end": 149, "text": "..............................................................................", "ref_id": null } ], "ref_spans": [], "eq_spans": [], "section": "~_R~PRE~SNTATION", "sec_num": "3." }, { "text": "+ .", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "~_R~PRE~SNTATION", "sec_num": "3." }, { "text": ". + ! (X Y Z, S.2($F)) !.. i with ref ! [ \"(RI: X/a, Y/b, Z/e, S 2/S ! ! !R2: X/aX, Y/bY, Z/cZ,' $F/(a,b,c,S.2($F))) ! \u00f7 .............................................................................. \u00f7", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "~_R~PRE~SNTATION", "sec_num": "3." }, { "text": "Exarllple of with r'ef cart in a r.h.s.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "Figure IO", "sec_num": null }, { "text": "X/aX,... means that the subcorrespondenoe (XYZ,S.2($F)) may be generated by rule R2, thereby identifying X in \u00d7YZ with ax in a\u00d7bYeZ (in the ].I~,s.).", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "R2:", "sec_num": null }, { "text": "In the ver'sTon of (Zaharin 86}, the correspondence is alv~,ays oF cor~st ituent type, because time only appl teat tons considered had been to m-structures used for L4T, where non--terminal nodes do not directly correspond to subst rings.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "R2:", "sec_num": null }, { "text": "But tills is by no means necessary, as the next example illustrates, with the language (an v bn cn 1 n>0). ................................................................................ \u00f7 !Rule RI: .......................................................................... .j !Rule R2: But something has to be added to dist ingu ish the STREE and SNODE parts.", "cite_spans": [ { "start": 107, "end": 189, "text": "................................................................................ \u00f7", "ref_id": null }, { "start": 200, "end": 277, "text": ".......................................................................... .j", "ref_id": null } ], "ref_spans": [], "eq_spans": [], "section": "R2:", "sec_num": null }, { "text": "+ .", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "R2:", "sec_num": null }, { "text": "(a b C , V(a, b, C)) ! ! ==> I ! (a,a) (v,V) (b,b) (c,c) ! \u2022 i .", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "R2:", "sec_num": null }, { "text": "(a x v b Y o Z , V.l(a, b, c, V.2($F)) I ! ==> ! ! (e,a) (v,V.1) (b,b) (c,c) (X v Y Z, V.2($F)) ! ! with ref ! ! (RI: X/a, Y/b, Z/C, V.2/V, SF/(a,b,c) ! ! !RE: X/aX, Y/bY, Z/cZ, V.2/V.1, $F/(a,b,c,V.2($F))) ! F:iguro ll: SI'CG for an v", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "R2:", "sec_num": null }, { "text": "We simply associate to each constant or\" variable appearing in a STCG rule one or two expressions represem ing the STREE and SNODE sequences, separated by a \"/\"", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "R2:", "sec_num": null }, { "text": "if necessary, with basic elements of the form \"p_q\", ~.~here p and q are constant or\" variab]e mdtces.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "R2:", "sec_num": null }, { "text": "In any given (,) Dair, we associate one such expression to each element of , and two to each node of , the first for STREE and the second for\" SN0bE. The second may be omitted: by default, SNODE is taken to be empty on internal nodes and equal to STREE on leaves.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "R2:", "sec_num": null }, { "text": "Our last example may now be rewritten as follows. + .................................................................... ", "cite_spans": [ { "start": 50, "end": 120, "text": "+ ....................................................................", "ref_id": null } ], "ref_spans": [], "eq_spans": [], "section": "R2:", "sec_num": null }, { "text": "! i SF ~:=> i (a,a) (b,b) (v,V.1) (c,c) (x v Y Z , V.2) I I i SF i wtth Per (RI: X/a, Y/b, Z/c, V.2/V, $F/(a,b,o) i IR2: X/aX, Y/bY, Z/cZ, V.Z/V. 1, $F/(a,b,c,V.2($F)))", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "R2:", "sec_num": null }, { "text": "Flgure 12: Extended STOG for an v bn cn", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "R2:", "sec_num": null }, { "text": "We will now give examples of STCBs which give rise to unnatural correspondences end try to derive some constraints on the rules. Let us first slightly modify our first STCG for an bn on. This is because the order of the elements of the strings is not compatible in the l.h.s, and in the r.h.s.: our first constraint will be to forbid this in STCG rules.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "R2:", "sec_num": null }, { "text": "Our second constraint will be to forbid the use of auxiliary variables which do not correspond to substrlngs (subtrees) of tme terminal (variable-free) pairs produced by the STCG.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "R2:", "sec_num": null }, { "text": "Let us illustrate this witl~ the following STCG, which constructs the representation tree S(A(u),B(v)) for each word w on (a,b,e) of even length such that w=uv and MU=NV. ................................................. There is a natural SSTC between the representation tree and the string. For example, we get S (A(a,b,c) ,B(b,a,c)) for w=abcbac, But the construction of this final correspondence involves the construction of pairs SUCh as (abcPPP,S(A(a,b,c),P,P,P)), w~ich are just used for counting.", "cite_spans": [], "ref_spans": [ { "start": 171, "end": 220, "text": ".................................................", "ref_id": null }, { "start": 315, "end": 324, "text": "(A(a,b,c)", "ref_id": null } ], "eq_spans": [], "section": "R2:", "sec_num": null }, { "text": "+ .", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "R2:", "sec_num": null }, { "text": "If we try to put sequence expressions on the P nodes and string elements, we notice that it would be necessary to extend the intervals of w, rather than to divide them, Otherwise, we would make the first P of aDoPPP correspond to the second b of w=abcbac, which is quite natural, but what would we associate to the first P of bBcPPP ? ]f we represent explicitly (and separately) the structure of a given (,) element of the SSTC by its derivation tree in the STCG, the second constraint will allow us to instantiate all variables by substrings or subtrees of and , wtthout having to construct other auxiliary strings and trees. This, of course,' would permit a mope economical ~mplementation, in terms of space.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "R2:", "sec_num": null }, { "text": "Finally, note that the interesting properties of SSTCs mentioned in Ill.l above have simple expressions as constraints on the rules of our extended STCG formalism.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "R2:", "sec_num": null }, { "text": "Trees have been widely used for the representation of naturat language utterances. However, there have been arguments saying that they are not adequate for representing the so-called 'discontinuous' structures. This has led to various solutions, relying, for instance, on encoding the desired information in the nodes (e.g. 'eoindexin9\"), or on oefining trees with \"discontinuous\" const i tuents.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "CONCLUDIN6 R~MARK~", "sec_num": null }, { "text": "We have presented here a proposal for representing discont inuous constituents, and, more generally, non-projective and uncomplete SSTCs with overlapping.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "CONCLUDIN6 R~MARK~", "sec_num": null }, { "text": "The proposal uses the ordinary definition of ordered trees. This is made possible by separating the representation tree from the surface utterance (which the tree is a representation of). The correspondence between the two may be represented explicitly by means cf sequences of intervals attached to the nodes.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "CONCLUDIN6 R~MARK~", "sec_num": null }, { "text": "This opens Up a discussion on (and definitions of) structured string-tree correspondences in general. Thls representation might also be used in syntactic editors for programs or In syntact~co-semanttc editors for NL texts.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "CONCLUDIN6 R~MARK~", "sec_num": null }, { "text": "Finally, the formalism of the String-Tree Correspondence 6rammar has been extended to glve the means of representing the said structured correspondences.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "64", "sec_num": null }, { "text": "analogous problem is to define structured correspondences between representation trees, for lnstanoe between source and target interface structures in transfer-based MT systems. We do not yet know of any satisfactory proposal.", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "An", "sec_num": null }, { "text": "A solution to this problem would give two very Interesting results:", "cite_spans": [], "ref_spans": [], "eq_spans": [], "section": "An", "sec_num": null }, { "text": "-first, a way to specify structural transfers in a reasoned manner, just as STCGs are used to specify structural analysers or generators, second, a way to put a text and its translation in a very fine-grained correspondence. This is quite easy with word-for-word approaches, of course, and also for approaches using classical (projective) PS trees or dependency trees, but has become qutte difficult with more sophisticated approaches using p-structures or m-structures. ZAJAC (1986) SCSL; ~ 1i~ sDeclflcatton n.~ :EO\u00a3 Proc. of COLING-88, IKS, 393-398, Bonn, August Z5-29, 1986 .", "cite_spans": [ { "start": 471, "end": 483, "text": "ZAJAC (1986)", "ref_id": null }, { "start": 528, "end": 577, "text": "COLING-88, IKS, 393-398, Bonn, August Z5-29, 1986", "ref_id": null } ], "ref_spans": [], "eq_spans": [], "section": "An", "sec_num": null } ], "back_matter": [], "bib_entries": {}, "ref_entries": { "FIGREF0": { "num": null, "text": "Example of discontinuity and displacement", "type_str": "figure", "uris": null }, "FIGREF1": { "num": null, "text": ".....................................................", "type_str": "figure", "uris": null }, "FIGREF2": { "num": null, "text": "Separation of a string and its \"dlsoontlnou8\" PS tree", "type_str": "figure", "uris": null }, "FIGREF3": { "num": null, "text": "..: .......... : .......... : .........Example of a \"dtsoonttnous\" dependency tree", "type_str": "figure", "uris": null }, "FIGREF4": { "num": null, "text": "if ok then x := a else x := a ~ ( b + e ) ! !01_23456\"/_89_10 1_12_13_14_15_16 \u00f7 .........................................................", "type_str": "figure", "uris": null }, "FIGREF5": { "num": null, "text": "Figure 6: Example of \"abstract\" tree for a formal language expression", "type_str": "figure", "uris": null }, "FIGREF6": { "num": null, "text": "nothing new has to be mentioned.", "type_str": "figure", "uris": null }, "FIGREF7": { "num": null, "text": "...............................................................", "type_str": "figure", "uris": null }, "FIGREF8": { "num": null, "text": "A slmp]e SCSG for an bn-cn X, Y and Z are string variables, SF ~ forest variable, and the indices are Just there to distinguish elements with the same label.", "type_str": "figure", "uris": null }, "FIGREF9": { "num": null, "text": "\u00f7 ................................................................+ IRule RI: (a b C , S(a, b, c......................................................... + Example of \"unordered\" STCG", "type_str": "figure", "uris": null }, "FIGREF10": { "num": null, "text": "..................................................... !Rule R2: ( x X Y P, S(A(x,$L),$M,, S(A($M),$F) ) ! + ....................................................... + F~gure 15: Example of STCG with auxiliary variables", "type_str": "figure", "uris": null }, "TABREF0": { "num": null, "type_str": "table", "html": null, "text": ".......................................................", "content": "
(McCawley 82) and later (Bunt & al 87} have argued that \"meaningful\" representations of sentences (2) and (3) should be the following phrase structure trees, (4) and (5), respectively. + ! I ! I ! ! ! I I ! I ! (5) I __ I I He picked the bali upl S I ! VP ! ! ! V ! ) NP ; I ! ! ! I ! ! !John talked of course about politics S (4) ! ! ! ! ! ! ~ ! ! ! ! ! ! NP ! VP I I ~1 I ! ! ! ! ! ! ! V ADVP PP ! ! ! ! ~ ! ! ! ! ! ! I ...
" }, "TABREF1": { "num": null, "type_str": "table", "html": null, "text": "................. ai ........", "content": "
NPNEG__.VP_
!!!!!!I
! JenepasVNPNP
!:::!!!I
! . ::: .donnelelul
" }, "TABREF3": { "num": null, "type_str": "table", "html": null, "text": "). \u00f7 ..........................................................", "content": "
!if then_else (01+2_3+6_7)(11)
!i
!!!!
!ok=: (4 5)=: (8_9)
! f12!_ !!!i!
!ax\" (10 11)x
!5634!?_8
!a+ (13_14)
! !910!!!
!b0
! !12_131415
" }, "TABREF4": { "num": null, "type_str": "table", "html": null, "text": "\u00f7 ........................................................ \u00f7", "content": "
!__~!II
!!!!II
! John of coursepoliticsHe___ballI
! ARGO ESTII~__ ARG1ARGO!ARe1 I
! 0 12 4[5_60 1the3 4I
!about2_3I
TOPIC!
!4_5He picked the ball up I
!01 2 3 4 5I
tI
! John talked of course about poltttcsI
!0I234.5__6I
" }, "TABREF5": { "num": null, "type_str": "table", "html": null, "text": "........................................................", "content": "
+
(14)V (0_7/2_3)V (0_7/2_3)(15)
I
!I!I!I!
A (0 Z) g (3_5) C (5_7)a.1 b.1 c. 1 V (1_3.4_5\u00f76_*/)
tI!0_13_45_6__!/23)
I!!!!!PI
la. 1 A b. 1 B c.1 C (6_*/)a.2 b.2 c.2
]0_1! 8_4I 5_6I12456_*/
a.2b.2e.2
l_Z4_56_*/
aavbbcc
O__ 1 __2__.3__4__5L7
Figure 8: Examples of p-etructures for al a2 v bl b2 cl
c2
" }, "TABREF9": { "num": null, "type_str": "table", "html": null, "text": ".a3.bl.bE.b3.cl.a2,03, as sho~ in the next diagram. ........................................................... ...............................................................", "content": "
impossiblewithourpreviousdefinitionsand
representations of SSTCs.
In the first element of R2, XYZ has been replaced by
ZYX. The following representation tree (16) would have
beennaturallyassociatedwiththestring
al.aZ.a3.bl.bE.b3.cl,cE,o3by our first STCG. With this
modtPlcation,itbecomesassociatedwith
a1.o2+
s,1 (09) !(16)
!It!
a.1b. 1c.IS.2 (1_3+4_6\u00f7? 9)
013467! I
!!!!
a.2b,2c,2S.3 (2~3\u00f75_6\u00f78_9)
784512I
___} .....
a.3b.3c.3
235_68_9
al\u00a2Za3blb2b3ola2c3
0__,__ 1 23__4__5__6__? __8+9
..\u00f7
Figure 14:Example of STC6 \"unordered\" w.r.t,the
etr lngs
The problem here is that the subtree rooted at S,2,
considered as e whole tree,should correspond to the
strtng a2.c3.b2.b3.c2.a3,and thatit corresponds to
02.a3.b2.ba.a2.c3when embedded in the whole tree rooted
at S,1.
The STREE Correspondences are not properly def ined,
becauseone should be able to distinguishbetween
different permutations of the Intervals, which is clearly
{,3
" }, "TABREF10": { "num": null, "type_str": "table", "html": null, "text": "", "content": "
{Bunt & a] 87) H.BUNT, J.THESINGH & K. VAN PER SLOOT
(1987)
Discontinuousognstttuents ~n .~~
~a~J~_g Proc. 3rd Conf. ACL European Chapter, Copenhagen,
April 1987.
{McCawley 82} J.D. MCCAWLEY (1982)
p~renthettoalanddiscontinuousconstituent
r~
Linguistic inquiry 13 (1), 913106, 1982.
{Vauquois 78] B.VAUQUOIS (1978)
Description \u00a3Le]_~ ~;~Jnterm6diatre
Communication pr~sent~e au colloque de Luxembourg,
April 1978, BETA document, Grenoble.
(Vauquois ~ Boiler 85} 8.VAUQUOI8 & CH.BOITET (1985)
~ranslat~cn6$.GETA ~University)
ComputationalLinguistics,11:1, 28-36, January
1985.
{Vauquois & Chappuy 85) B.VAUQUOIS & S.CHAPPUY (1985)
~crammers
Proc. Conf. on theoretical & methodological issues
in MT, Colgate Univ., Hamilton, N.Y., August 1985.
(Zahartn 86] Y.ZAHARIN (1986)
t rB_~Leg.t~ a~ ~m t~e n ]~v.~j~ ~. tD_~Z~!
Ph.D. Thesis, Untverstti Salns Malaysia, March 1986
(Research conducted under GETA-USM cooperation GETA
document, Grenoble.
(Zahartn 87a} Y.ZAHARIN (1987)
Strina-Tree Correspondence ~8
r~~gg_f~tr~ corresoondence I~
of ~and tree structures?
Prec. 3rd Conf. ACL European Chapter, Copenhagen,
April 1987.
{Zaharin 8?b} Y.ZAHARIN (1987)
The ~~at FE..TAz = ~v_qQa~L~
thejournal TECHNOLOGOS (LISH-CNRS), prlntemps,
1987, Paris.
(ZaJac 86] R.
" } } } }