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<?xml version="1.0" standalone="yes"?> <Paper uid="E91-1046"> <Title>THE TEXTUAL DEVELOPMENT OF NON-STEREOTYPIC CONCEPTS</Title> <Section position="4" start_page="0" end_page="0" type="metho"> <SectionTitle> 1 INTRODUCTION </SectionTitle> <Paragraph position="0"> In the field ofknowledge-bMed text analysis it has been regarded as insufficient to analyze a text against the background of static and stereotypic default assumptions for some time (cf. \[Hellwig84\], \[Scha/Bruce/Polanyi87\]). By applying this method the pre--coded concepts are invoked again and again during the process of text analysis, regardless of the changes land the new concepts being constituted by the ongoing text. The function of a text, however, is not confined to concept selection as in current knowledge-based applications. In addition, textual mechanisms are used to operate on concepts and to compose them to actual contexts, i.e. to constitute (new) concepts. Textually the contexts are established by the thematic and by the referential structure. Thus, new mechanisms are required which permit the textual organization to control the creation and manipulation of concepts in text processing. In a way, this is to tie linguistic and knowledge,-based approaches to text processing together into a single method.</Paragraph> </Section> <Section position="5" start_page="0" end_page="0" type="metho"> <SectionTitle> 2 THE KONTEXT MODEL </SectionTitle> <Paragraph position="0"> The basic premise of the KONTEXT model is that the relationship of expression and concept are changed during a text and concepts are communicated by using the mechanisms of text constitution. The KONTEXT model is based on the assumption that * the information conveyed in a text and the information describing its contextual organization can be structured into five layers. They define the sentence structure, information on thematic progression, the referential structure, the conceptual representation of the text and the conceptual background knowledge; * discourse provides the basic mechanisms by which concepts are constructed. Discourse is defined as sequences of transitions between discourse states and discourse states are defined by the information represented in the layers.</Paragraph> <Paragraph position="1"> The text analysis component constructs and traverses the information of these layers under control of the discourse development. In this way, it can incrementally construct a textual view on knowledge, rather than only recognizing precoded concepts.</Paragraph> <Paragraph position="2"> We will now describe the layers of the text repre- 263 sentation. In the following section we discuss the conception of discourse in more detail.</Paragraph> </Section> <Section position="6" start_page="0" end_page="0" type="metho"> <SectionTitle> 2.1 LAYERS OF TEXT REPRESENTA- TION </SectionTitle> <Paragraph position="0"> There are five layers of text representation: sentence structure thematic structure referential structure view background knowledge The lowest layer is the basis for textual communication. It is a formal representation of concepts modeling an open world and serves as background knowledge. Since we allow for the constmction of new details and concepts, an organization of concepts is provided which supports this task. Our background knowledge differs from traditional knowledge bases in that it does not represent a particular domain model which assigns a predefined and fixed structure to the concepts. It is rather organized around expressions and models their referential potential in terms of concepts. It resembles a meaning dictionary (like e.g. \[COBUILD87\] which is used as the basic material), where with expressions concepts are constituted and used to explain other concepts. Basically all concepts are of the same rank with respect to an open world. During discourse the concepts are accessed via explicitly modeled perspectives on them \[Kunze90\] \[Melcuk87\] depending on the actual textual development (e.g. actual state of contexts, c.f. 2.2 discourse state).</Paragraph> <Paragraph position="1"> The next layer, the view, models the subject matter of the text using the concepts which are defreed in the background knowledge. The ongoing discourse selects concepts from the background knowledge or the already existing view, reorganizes their structure and (re-)integrates them coherently into the already existing view. The concepts constructed in the view during discourse provide the text specific perspective on the background knowledge.</Paragraph> <Paragraph position="2"> The layer of the referentialstructure represents reference objects and their relationships. It drops details of the concept definition in accordance with the abstraction level of references in the text, and represents those complexes as units which are explicitly referred to by linguistic means in the text.</Paragraph> <Paragraph position="3"> The layer of thematic structure traces the discourse development. It represents the contextual clustering of reference objects and traces the development of their clustering. This trace represents the progression of themes and the development of focusing. The notion of thematic structure is based on the Prague School approaches to the thematic organization (e.g. \[Danes70\] \[Hajicov~ Sgal188\]\[Hajicov~i/Vrbov~2\]), which we refine by distinguishing the mechanisms involved in terms of the textual function of linguistic means with respect to the different layers of the text representation. null In our model the units of the layer of thematic structure are contexts. By context we understand a cluster of reference objects, where within a context the relationship between a reference expression and its reference object is unequivocal. During the ongoing discourse, however, this relationship and the groups of reference objects which are clustered together change. Whether or not linguistic means create new contexts, and which kind of clustering of reference objects they effect, depends on their textual function and on the state of discourse they operate on (examples of this are given below). Contexts are the units of the thematic progression. It is this grouping of reference objects that is referred to by linguistic means immediately, that is changed, resumed, revised and tied up to during discourse. The thematic structure is the result of creating, dosing and referring to contexts. The movement of contexts traces the growth of the view.</Paragraph> <Paragraph position="4"> It should be noted that complex progression types earl be constructed. This is due to the ability of predicative expressions to cover several themes by virtue of their arity and due to the textuM~ possibility of changing the structure of a contextually clustered concept by changing the focus when referring to a context. Therefore hierarchical structures as proposed by different approaches to describing the structuring of actual texts are not sufficient to cope with the ability of natural language texts to constitute contextual relations (of. content - 264 oriented structures: e.g. thematic progression \[Danes70\] - at least the five forms elaborated are hierarchical -), or discourse segmentations: e.g.</Paragraph> <Paragraph position="5"> discourse constituent units \[Polanyi88\], context spaces \[Reichman85\], rhetorical structures \[Mann/Thompson88\], superstructures and macrostructures \[vanDijk83\]).</Paragraph> <Paragraph position="6"> The sentence structure describes the linguistic means used in the text to express the information encoded in the lower layers.</Paragraph> <Paragraph position="7"> Our representation models structural relationships of text constitution principles. The background knowledge provides concepts for the consritution of the semantic text representation (view). The concepts constructed in the view during discourse provide the text specific perspective on the background knowledge.</Paragraph> <Paragraph position="8"> Referential structure and thematic structure each cluster structures of the lower layers. Reference objects group conceptual definitions into units which can be referred to by ensuing linguistic expressions. The sequence of thematizing defines a clustering of reference objects into contexts.</Paragraph> <Paragraph position="9"> Whilst the lower layers contain more static informarion which is independent of the actual sequence of the textual presentation, the dynamic of discourse, i.e. the growth of the view during the ongoing discourse, is represented in the layers of thematic structure and sentence structure.</Paragraph> <Paragraph position="10"> The modeling allows for a text driven control of operations on the knowledge base and on the view, because the manipulations of the lower layers depend on the interpretation of the upper layer phenomena. null We define the types of manipulations necessary in terms of the contribution linguistic means make to the layers of the text representation. The clef'tuitions are placed in a text lexicon (of. the example given below).</Paragraph> <Section position="1" start_page="0" end_page="0" type="sub_section"> <SectionTitle> 2.2 DISCOURSE </SectionTitle> <Paragraph position="0"> By discourse we understand a sequence of state transitions which is guided by the interpretation of linguistic means. It models textual access to concepts: A text does not communicate concepts at once. It rather guides sequential access and operations on knowledge that produce a particular view on the concepts of the background knowledge.</Paragraph> <Paragraph position="1"> A discourse state is defined by the actual state of all the five layers of the text representation, which renders the actual state of the view and the actual access structure to view and background &quot;knowledge. While the view grows during the mmlysis, only a small segment of it is in the focus of attention at one state, and the objects which are retbrred to by linguistic expressions may change state by state. A discourse state provides the immediate context to which ensuing linguistic means can refer directly, and also previous contexts. null The transition of a discourse state is the effect of the interpretation of alinguistic expression. It is determined by the textual function of linguistic means. Modeling the operational semantics of linguistic means within the framework outlined leads to our text lexica.</Paragraph> <Paragraph position="2"> Differences of the view of two discourse states which are produced by a discourse state transition can be regarded as the semantic contribution of a linguistic expression. But it is important to note that this contribution is not only determined by the isolated expression, and that therefore analysis does not involve a static mapping from a textual expression to some semantic representation or vice versa. The contribution rather depends on the actual state of the preceding discourse on which the expression operates. Note also that there are expressions whose interpretation does not contribute to the growth of the view. In an actual text they rather are used in order to manipulate the thematic organization (e.g. redirections).</Paragraph> </Section> </Section> <Section position="7" start_page="0" end_page="0" type="metho"> <SectionTitle> 3 EXAMPLE </SectionTitle> <Paragraph position="0"> With a small example we illustrate how the KONTEXT model works. We show how a reference object and a concept corresponding to a referential expression is created, and how the relationship between expression and concept is changed duringthe discourse. From a sample text we take the following sentence and show that discourse state transitions already occur while interpreting this sentence textually: &quot;The electronic.: dictionaries that are the goal of EDR will be dicaonaries of computers, by computers, and for computers.&quot; We provide a selection of three discourse states showing view and access structure after the interpretation of &quot;The electronic dictionaries&quot; (figure - 265 l), after &quot;that are the goal of EDR&quot; (figure 2), and after &quot;will be dictionaries of computers, by computers, and for computers.&quot; (figure 3). Each figure then is explained by describing the textual function of the linguistic means concerned, i.e. by describing how they operate on previous discourse states and what their contribution to the layers of the text representation is. These definitions are placed in a text lexicon. Because we want to draw the attention to the nature of textual functions of linguistic means and to the possibility to distinguish and to describe these functions with respect to the layers of the text representation, we confine ourselves to demonstrating this by discussing only those readings which lead to a solution in our example. null The sentence structure used is the structure the PLAIN grammar \[Hellwig80\] attributes to a sentence, and for the graphical representation of our example we use the conventions explained in the legend (see below). The names of the roles in the view and in the background knowledge have been chosen for mnemotechnical reasons only, they are not to be confused with the conceptual modeling of prepositions.</Paragraph> <Paragraph position="1"> &quot;The electronic dictionaries&quot;: In the sentence structure the reference expression &quot;the electronic dictionaries&quot; occurs. Since so far no corresponding reference object exists, it must be created and conceptually defined. No previous textual context has been established before this state, therefore immediate access to the global and unspecified background concepts is allowed. \[COBUILD87\] which means that in the background knowledge no corresponding concept exists.</Paragraph> <Paragraph position="2"> &quot;electronic&quot;: As an adjective, &quot;electronic&quot; refers to the reference item --elX-, which does not select a concept, but a conceptual structure which is used to extend or to modify the dominating noun's concept. In \[COBUILD87\] there are two conceptual aspects of &quot;electronic&quot;, which are related to each other. At first &quot;electronic&quot; can be'a device, which has silicon chips and is used as a means for electronic methods'. Secondly 'a method' can be referred to as &quot;electronic&quot;.</Paragraph> <Paragraph position="3"> &quot;dictionary&quot;: Initially &quot;dictionary&quot; refers to the reference object <diet>. Conceptually &quot;dictionary&quot; can refer to two aspects: It can refer to' a physical device, which is made of paper and serves as a medium for recording symbols; it has been compiled by an author and is used for reference purposes.' It can also refer to 'the recorded symbols as a work'.</Paragraph> <Paragraph position="4"> - 266 &quot;electronic dictionary&quot;: In order to find a conceptual definition of the imroduced reference object <eldict> we create a less specific abstract concept of dictionary. On the one hand it must be as specific as possible, and on the other hand it must be compatible with what is known conceptually about the referential item --elX-. 'Electronic dictionary' then is a combination of 'electronic' and 'dictionary' leaving open e.g. the incompatible device 'paper'. A more specific concept of &quot;dictionary&quot; is introduced. This: means that from now on the text will not deal with &quot;dictionaries&quot; in general, but with &quot;dictionaries&quot; in the restricted context of &quot;electronic dictionaries&quot;. Therefore a new context is opened, and in this new context &quot;dictionaries&quot; refers to a new reference object <eldict> which can be the theme of the further ongoing dis- null &quot;The electronic dictionaries that are the goal ofF.DR .... &quot; &quot;that&quot;: This relative pronoun, again, forces the creation of a new context. A new context is opened which is restricted to those &quot;electronic dietionaries&quot; only, which &quot;are the goal of EDR&quot;. The pronoun also has the function of a connexion instruction \[Kallmeyer/eta177\] and effects a referential equation of &quot;electronic dictionaries&quot; and what is predicated about &quot;that&quot;. Both expressions and also &quot;that&quot; then refer to <eldictEDR> in this new context.</Paragraph> <Paragraph position="5"> &quot;are&quot;: It is the textual function of the copula to form a unified context of the contexts of its subject (&quot;that&quot;) and its predicative complement (&quot;the goal ,,Fig. 3 : Discourse state after the interpretation of ,, .will be dictionaries of computers, by c., and for c.</Paragraph> <Paragraph position="6"> &quot;dictionaries&quot;: The expression &quot;dictionaries of computers, by computers, and for computers&quot; refers to three reference objects <dictl>, <dict2> and <diet3> (namely &quot;dictionary&quot; in the context - 267 of&quot;of', &quot;by&quot;, and &quot;for&quot;). The three contexts established for these reference objects are textually focused on and thus provide the basis for further textual progression.</Paragraph> <Paragraph position="7"> &quot;will be&quot;: The copula, again, forms a unified context of the contexts of its subject and its predicative complement. This also effects a referential equivalence of &quot;electronic dictionary&quot; and &quot;dietionary&quot;. Therefore &quot;dictionary&quot; must at this state of the discourse no longer access the concept of &quot;dictionary&quot; of the background knowledge as freely as at the beginning of the text, when there was no restriction in interpretation. Now it rather must access the concept which meanwhile has been established by the text (namely 'dictionary' in the sense in which it has been modified and defreed by 'electronic').</Paragraph> <Paragraph position="8"> &quot;of, by, for&quot;: make further conceptual contributions to the concept of &quot;electronic dictionaries&quot; by refining the concept by the aspects denoted by &quot;of&quot;, &quot;by&quot; and &quot;for&quot;.</Paragraph> </Section> class="xml-element"></Paper>