Testing Structural Properties in Textual Data: Beyond Document Grammars

Transcription

1 Teting Structural Propertie in Textual Data: Beyond Document Grammar Felix Saaki and Jen Pönninghau Univerity of Bielefeld, Germany Abtract Schema language concentrate on grammatical contraint on document tructure, i.e. hierarchical relation between element in a tree-like tructure. In thi paper, we complement thi concept with a methodology for defining and applying tructural contraint from the perpective of a ingle element. Thee contraint can be ued in addition to the exiting contraint of a document grammar. There i no need to change the document grammar. Uing a hierarchy of decription of uch contraint allow for a claification of element. Thee are important feature for tak uch a viualizing, modelling, querying, and checking conitency in textual data. A document containing decription of uch contraint we call a context pecification document (CSD). We decribe the baic idea of a CSD, it formal propertie, the path language we are currently uing, and related approache. Then we how how to create and ue a CSD. We give two example application for a CSD. Modelling co-referential relation between textual unit with a CSD can help to maintain conitency in textual data and to explore the linguitic propertie of co-reference. In the area of textual, non-hierarchical annotation, everal annotation can be held in one document and interrelated by the CSD. In the future we want to explore the relation and interaction between the underlying path language of the CSD and document grammar. Correpondence: Felix Saaki, Univerity of Bielefeld, Faculty of Linguitic and Literature, Computational Linguitic and Text- Technology, Bielefeld, Germany. felix.aaki@uni-bielefeld.de 1 Introduction Thi paper decribe reearch carried out in the project Secondary information tructuring and comparative dicoure analyi (SEKIMO), which i part of the reearch group Text-technological modelling of information and i funded by the German Reearch Council (DFG). In our project, we ue XML document grammar, i.e. DTD (Bray et al., 2000), XML Schema (Thompon et al., 2001), and Relax NG (Clark and Murata, 2001) to formalize and interrelate linguitic phenomena in typologically divere language. The document grammar differ in what they decribe, i.e. morpho-yntactic tructure, emantic relation, and dicoure function, and in the granularity of the decription, i.e. there are language or dialogue Literary and Linguitic Computing, Vol. 18, No. 1 ALLC 2003; all right reerved 89

2 F. Saaki and J. Pönninghau type pecific document grammar on the one hand and document grammar of a more general kind on the other hand. At the level of econdary information tructuring, we interrelate the document grammar, ometime creating intermediate document grammar to connect the pecific and general level of linguitic decription. All document grammar are developed on the bai of and applied to dialogue and text corpora in different language. (For more information about the project, ee Schema language uually define grammatical contraint on document tructure, i.e. hierarchical relation between element in a tree-like tructure. Epecially, but not only for the linguitic phenomena we want to decribe, it eem ueful to complement the concept of hierarchical validation with a methodology for defining and applying other tructural contraint, a there are everal limitation in implementing appropriate document grammar. The main benefit of thi methodology are: addition of contraint that are hard to expre uing chema language; independent formulation of contraint; adding new contraint doe not require change to document chema; claification of information item; aigning clae baed on fulfilment of contraint. We will exemplify thi in reference to the document hown in Fig. 1, which i baed on the Englih part of the MULTEXT-EAST corpu (Ide and Véroni, 1994). Fig. 1 Annotation of a paragraph from Literary and Linguitic Computing, Vol. 18, No. 1, 2003

3 Teting Structural Propertie in Textual Data Hierarchical contraint for the name element are, for example, that it ha to occur inide a entence, here tagged a. Thee contraint can alo be decribed in term of contextual contraint for name, i.e. it ancetor ha to be an element. The hierarchical and the contextual contraint are hown in Fig. 2. In the left-hand part of Fig. 2 there i the hierarchical contraint for name element, i.e. they occur in the content model of entence. In the right-hand part the relation between name and i decribed a a contextual feature of name, hown by arrow pointing from name element to element. Thi feature i hared by all name element. Other feature are hared by only ome name element. For example, the firt occurrence of name i at the beginning of a entence. The ame i true for the fourth occurrence of name, hown by the dark background of the two element. They can be further claified: the firt name i inide a entence, which i at the beginning of a paragraph p, the fourth name i inide a ubequent entence. In other word, the contextual feature of element can be organized in term of a cla tructure, with clae containing general propertie and ubclae that define more pecific propertie. For tak uch a viualizing, modelling, querying, and checking conitency of text, it might be very ueful to decribe the contextual feature of element and arrange them in a cla tructure. A document containing uch decription we call a context pecification document (CSD). In thi paper we will dicu the baic idea of a CSD and decribe how to create and ue a CSD. We will then give two example application for a CSD, namely modelling co-reference in a language-pecific or general fahion, and interrelating different annotation of text. 2 What i a CSD? 2.1 Formal propertie of a CSD A CSD i an XML document that model a hierarchical organized et of clae given by context decription. In the terminology of a CSD, a corpu corpu p... p... name name name name name q q q name name name name name q q q Fig. 2 Hierarchical and contextual contraint on element. Literary and Linguitic Computing, Vol. 18, No. 1,

4 F. Saaki and J. Pönninghau context i a et of element node within an XML document that hare ome pecific tructural property. The hierarchy i contructed by ubetting context. The hierarchy of context clae require each ubcla to decribe a ubcontext of the upercla, i.e. the tructural tet performed ha to be more pecific. Subclae of the ame upercla are not required to form a proper decompoition, o there may be ome ubcontext haring everal node. In our example of the name element in Fig. 2, the general context decription i that their ancetor i an element. The firt occurrence of name and it fourth occurrence can be decribed a a ubcla, becaue they are the firt child of an element. The firt occurrence of name form another ubcla, becaue it i at the beginning of an element that i at the beginning of a paragraph p. We have choen caterpillar expreion a decribed by Brüggemann- Klein and Wood (2000) to formalize the tructural propertie that form the et of context-node. A caterpillar expreion i a regular expreion over an alphabet of ymbol for move (left, right, up, firtchild, latchild), name of element, and everal ymbol for poitional tet (iroot, ileaf, ifirt, ilat). Only element node are ubject to a caterpillar expreion and it evaluation. For example, in Fig. 2, the fourth occurrence of name i the firt child of, o it i matched by a caterpillar expreion uch a ifirt. The textual data from where (ee Fig. 1) preceding the name element i not ubject to the evaluation of the caterpillar expreion. We will not give a lengthy decription of the exact emantic of thee expreion but will concentrate on their application to markup over textual data. The interpretation of each ymbol can be graped intuitively, when we imagine a caterpillar crawling in the element tree. The ymbol right map to true and a change of the current node of the caterpillar to the right ibling, if there exit uch a right ibling. Otherwie, the move evaluate to fale and the current-node remain the ame. Other move, uch a upor left are defined analogouly. Element name and poitional tet are Boolean predicate (e.g. ifirt) and check the current-node for pecific propertie, e.g. ifirt evaluate to true, if the current-node i the firt child of it parent. A caterpillar expreion evaluate to true with repect to ome arbitrary initial node, i.e. the teted node belong to the context, if there i a mapping of the expreion to a equence of ucceful move and tet in the element tree. 2.2 Related approache CSD might reemble Schematron (Jelliffe, 2001), a both can be ued to partially validate document via decription of permiible path for element, but in fact CSD differ from thi approach in everal apect. Firt, Schematron ue XPath (Clark and DeRoe, 1999) to pecify the path, which i more expreive than caterpillar expreion. Undoubtedly thi eae decribing context. However, we are intereted not only in modelling context but alo in comparing and relating contextdecription to document grammar o a to be able to compare their 92 Literary and Linguitic Computing, Vol. 18, No. 1, 2003

5 Teting Structural Propertie in Textual Data trength and weaknee for (linguitic) modelling. Hence, le expreive language eem to be better uited. Second, Schematron almot only deal with reporting fail tet, wherea CSD i epecially deigned for claification of node, i.e. to aign the et of context the node belong to. We can think of CSD a a mean for weak typing a it can be found in everal query language. Certainly, one can mimic thi uing Schematron named pattern, but at the expene of loing ome level of abtraction. Neverthele, CSD and Schematron hare the capability to decribe and validate document baed on an open, node-centric view intead of the top-down hierarchical approach forced by document grammar. CSD can alo be compared with the declaration of feature tructure in the Text Encoding Initiative (TEI; Sperberg-McQueen and Burnard 1994). The baic idea i the ame, namely, to ue an additional document to pecify propertie of the baic data in form of contraint. Similar to Schematron, the expreive power of the TEI feature tructure i much higher than that of caterpillar expreion. However, a mentioned above, for our theoretical interet in the relation between grammatical and path expreible contraint a retriction to a le expreive language eem to be worth while. 2.3 How to write a CSD The tructure of the CSD and the output document of proceing i formulated uing the DTD formalim. An intance of a CSD i illutrated in Fig. 3. A CSD i aware of namepace, whoe tuple of prefix and URI can be introduced in the namepace element inide the namepacelit. The tet for element then may ue thee prefixe. A a CSD validate or querie partial document tructure, we need to define only thoe element that we conider relevant to the proce of querying or validation (ee below). Thi i pecified by the cope attribute, which i attached to the upercla element. The value of cope can be a ingle element name or a white-pace eparated lit of element name. A CSD that define context for the element name (ee Fig. 2) therefore contain a upercla element with an attribute cope= name para.... Next we contruct caterpillar expreion. A poible tart node of a Fig. 3 The general tructure of a CSD given by example. Literary and Linguitic Computing, Vol. 18, No. 1,

6 F. Saaki and J. Pönninghau caterpillar i taken from the cope attribute. For each move or tet of a caterpillar, we ue the appropriate CSD element, i.e. up, right, left, firt, lat, iroot, ileaf, ifirt, ilat. 1 The name of an element i teted by element name= ome element name. For example, we can tet whether an element i the ancetor of the name element by uing an expreion uch a up,. The CSD element zeroormore repreent the Kleene-tar operator, e.g. known from DTD. The element right and name a the content of zeroormore mean zero or more occurrence of the element name to the right of the current node. Thi caterpillar expreion would match for all occurrence of the name element in Fig. 2. Now we contruct the hierarchy of caterpillar expreion. The clae are arranged in an inheritance tructure, i.e. the teted propertie of a certain cla n are common to all ubclae neted in n. Figure 4 how the cla tructure we have decribed o far for the name element. With thi CSD, we are able to claify the firt occurrence of name a a member of the cla name-ub2, the fourth occurrence of name a a member of the cla name-ub1, and the other occurrence a a member of namegeneral. It hould be noted that the common ubequence of the caterpillar expreion are omitted a they are implied by the cla hierarchy. 2.4 How can a CSD be ued? Two contruct in the CSD in Fig. 3 have not been explained o far, i.e. the mode attribute on the cd element and the ufficient attribute on ome of the cla intance. Thee attribute are important parameter a we apply the CSD to a document intance. We can either tet if a document intance i valid with repect to ome context pecification or query for the et of clae matched by certain element node. The mode attribute and it permiible value validate veru query determine the mode of proceing. Context (clae) can be tated to be neceary but not ufficient for validating or querying a node. The ufficient attribute i attached to 1 Experienced uer may give path expreion a attribute value uing concie notation. Fig. 4 The cla tructure of a CSD decribing contextual propertie of the name element in Fig Literary and Linguitic Computing, Vol. 18, No. 1, 2003

7 Teting Structural Propertie in Textual Data a cla if thi cla lead to a poitive reult in the query or validation. For example, if we are intereted in querying name element in our example document (ee Fig. 1) that are at the beginning of a entence, we would attach the ufficient attribute only to the name-ub1 cla and et the mode to query. If we imply want to enure that all name are inide entence, we would attach the ufficient attribute to the namegeneral cla and et the mode to validate. In ome cae it might be ueful to et validity contraint for certain element node in the document intance to enure that a pecific element matche a pecific cla. For thi purpoe we introduced the cd: caterpillar attribute defined in the namepace text-technology.de/cd. Thi attribute can be attached to element in the document intance. The CSD-proceor will generate an error for thi element if it i not in accordance with the cla pecified in the value of cd:caterpillar. In our example, we could attach the cd:caterpillar attribute with the value name-ub2 to the firt occurrence of the name element, to enure that it i alway in the firt entence. The following lit ummarize how to create and ue a CSD: chooe one or more XML document to be validated or queried; chooe an element name or a group of element name; write caterpillar expreion to be matched by the element; contruct a cla hierarchy for the caterpillar expreion; chooe clae to be ufficient for validation or query; write a CSD; optionally, attach the cd:caterpillar attribute to certain node in the document intance(); chooe a proceing-mode for the CSD, i.e. validate or query. 2.5 Poible reult of applying a CSD to a document intance After proceing a document intance in query mode, an output document i generated (Fig. 5). The output document contain a collection of nodelit element, one for each upercla defined in the CSD. The cope attribute of each Fig. 5 The output document of a query. Literary and Linguitic Computing, Vol. 18, No. 1,

8 F. Saaki and J. Pönninghau nodelit carrie the ame value a in the CSD. The location of the document intance i contained in the url attribute of the document element. Each nodelit conit of at leat one node, pecifying an abolute path to the repective node in the document intance. The path i expreed in XPath-Syntax, o the output document can be eaily proceed, e.g. with XSLT (Clark, 1999). For each ufficient cla matched by the node, there i a cla element holding the name of that cla and an optional comment taken from the CSD. The reult of validating a document intance i either true or fale. A document i erroneou if any node in the intance named by the cope attribute doe not match any cla regarded a ufficient, or if the cla named by the cd:caterpillar attribute i not a member of the et of matching clae. That i, the correponding caterpillar expreion of the given cla evaluate to fale for that pecific node. Suppoe we attach the cd:caterpillar attribute with the value name-ub2 to the econd occurrence of name, then an error would occur becaue the expreion up ifirt i not true for thi node. 3 Example Application for a CSD 3.1 Modelling of co-reference In Saaki et al. (2002), we preent an approach toward a formal decription of co-reference in different language, uing the expreive power of document grammar. There we create general and language-pecific document grammar for language corpora. In thi paper we will not give a detailed decription of thi approach, but try to exemplify how the decription of element clae in contextually pecified document tructure might contribute to a claification of co-referential relation, complementing the approach of document grammar. Let u conider the example in Fig. 6, which i a lightly modified verion of the example in Fig. 1. The noun phrae Minitry of Truth, tagged a name, co-refer with the pronoun it, which i tagged a pron in the econd entence. Minitrue alo co-refer with the noun minitrue in the ame entence, which i tagged a name. In the third entence, there i another pronoun pron, which refer to the three quotation q. Figure 7 how the tructural propertie of the three co-referential unit and a correponding CSD. Minitrue can be related to Minitry of Truth with the caterpillar expreion left name. The firt occurrence of the pronoun pron can by related to Minitry of Truth with another caterpillar expreion up up ifirt* name. And the econd pronoun pron can be related to the three quotation q via the caterpillar expreion (right* q)*. The viualization of the CSD how how thee tructural pecification can be claified. Thi example how how one might ue a CSD in the field of linguitic. It can be a tarting point to decribe tructural propertie of 96 Literary and Linguitic Computing, Vol. 18, No. 1, 2003

9 Teting Structural Propertie in Textual Data Fig. 6 Co-referential unit. certain co-referential phenomena and to allow u to tet them with annotated textual data beyond the practical limitation of document grammar in a general and more or le (language) pecific fahion. 3.2 Interrelating different annotation of text There ha been a long continuing dicuion on how to repreent concurrent hierarchie in document tructure. One ource of thi dicuion i the OHCO hypothei that text i a ordered hierarchy of content object. There are many weak and trong verion of thi hypothei. Some worker (Caton, 2002) even claim that the idea of text a a hierarchical tructure i jut one plauible view among other. We do not claim to be able to contribute new idea for thi dicuion or a olution for the problem. What we want to try i to interrelate different annotation with a CSD. We repreent one primary annotation in the ordinary XML document tructure and another annotation, in the ame document, with anchor element. A type can be aigned to thee anchor via the cd:caterpillar attribute, and the repective clae in the CSD can pecify the tructural contraint for the anchor. Figure 8 how an example of a primary annotation from a linguitic Literary and Linguitic Computing, Vol. 18, No. 1,

10 F. Saaki and J. Pönninghau corpu p... coref-general (up*, left*, right*, ifirt*, name*, q*)* pron pron ub1 left, name ub2 up*, ifirt*, name ub3 (right*, q)* name name name name name q q q perpective, which mark entence with tag, and a econdary annotation, which mark line with line-begin and line-end. With the CSD, it i poible to pecify different type of relation between the annotation of entence and line. We can define a cla normalline for general line, which follow immediately a line-end element. The repective caterpillar expreion for thi cla i left line-end. The ubcla lat-line-begin ha the caterpillar expreion right* line-end ilat up corpu. There i alo a cla that cannot be ubumed under the normalline cla. Thi cla i called identicaltosentence and ha the caterpillar expreion ilat up. Thi methodology i cloely related to olution for the problem of overlapping hierarchie, a propoed by the TEI. One of the TEI olution i the contruction of virtual joint for fragmentary element. A CSD can be ued for thi purpoe a well, but alo, a in our example, to decribe variou clae for the intance of the econdary annotation. Thee then can be ued to tet hypothee about the relation between two different annotation of text. Our methodology ha ome drawback, epecially the fact that o far it i not yet poible to generate the caterpillar expreion automatically. Neverthele, it can be ued to validate a hypothei about the relation between different annotation of the ame textual data. Fig. 7 Structural propertie of co-referential unit in Fig. 6 and a correponding CSD. 4 Summary and Future Work In thi paper, we have decribed the motivation for the contextual pecification of element and their repreentation in a cla tructure. We have preented the main apect of CSD a a framework and ome example. Two application in the domain of co-reference and the modelling of different annotation of text howed the potential of CSD. A prototype of a CSD proceor ha been implemented in the Python programming language. In the future we will continue reearch on everal ubject. A decribed, currently we follow Brüggemann-Klein 98 Literary and Linguitic Computing, Vol. 18, No. 1, 2003

11 Teting Structural Propertie in Textual Data Fig. 8 An annotation of line and entence. and Wood in retricting the operator to equence, bracket, and Kleenetar. However, we expect optionality? to be highly valuable to impoe locality contraint (e.g. at mot three node to the left? left? left?) and therefore conider extending our notion of caterpillar expreion in that ene. A CSD ue but doe not depend on a pecific path language, it i eay to integrate, for example, XPath or other (path) language with minor modification to the CSD-DTD, a path expreion may be given a attribute value a well. Furthermore, we want to explore in more detail the relation between a CSD baed on caterpillar expreion and document grammar. And lat but not leat, we want to Literary and Linguitic Computing, Vol. 18, No. 1,

12 F. Saaki and J. Pönninghau ue the CSD to model linguitic phenomena on large corpora a another approach to econdary information tructuring. Reference Bray, T., Paoli, J., Sperberg-McQueen, C. M., and Maler, E. (2000). Extenible Markup Language (XML) 1.0, 2nd edn. W3C Recommendation, 6 October (acceed 6 April 2003). Brüggemann-Klein, A. and Wood, D. (2000). Caterpillar: a context pecification technique. Markup Language: Theory & Practice, 2(1): Caton, P. (2002). Markup current imbalance. Markup Language: Theory & Practice, 3(1): Clark, J. (1999). XSL Tranformation (XSLT). W3C Recommendation, 16 November (acceed 6 April 2003). Clark, J. and DeRoe, S. (1999). XML Path Language (XPath). W3C Recommendation, 16 November (acceed 6 April 2003). Clark, J. and Murata, M. (2001). Relax NG Specification. OASIS Committee Specification, 3 December relax-ng/pec html (acceed 6 April 2003). Ide, N. and Véroni, J. (1994). Multext (multilingual tool and corpora). Proceeding of the 15th CoLing, Kyoto. Sheffield: ICCL (International Committee on Computational Linguitic), pp Jelliffe, R. (2001). Schematron an XML tructure validation language uing pattern in tree. (acceed 6 April 2003). Saaki, F., Wegener, C., Witt, A., Metzing, D., and Pönninghau, J. (2002). Coreference annotation and reource: a multilingual corpu of typologically divere language. Proceeding of the 3rd International Conference on Language Reource and Evaluation (LREC-2002), La Palma. Pari: ELRA (European Language Reource Aociation), pp Sperberg-McQueen, M. and Burnard, L. (ed) (1994). Guideline for Electronic Text Encoding and Interchange (TEI P3). Chicago/Oxford: ACH/ACL/ALLC. Thompon, H., Beech, D., Maloney, M., and Mendelohn, N. (2001). XML Schema Part 1: Structure. W3C Recommendation, 2 May w3.org/tr/xmlchema-1 (acceed 6 April 2003). 100 Literary and Linguitic Computing, Vol. 18, No. 1, 2003