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<?xml version="1.0" standalone="yes"?> <Paper uid="W01-0810"> <Title>Linear order as higher-level decision: Information Structure in strategic and tactical generation</Title> <Section position="3" start_page="0" end_page="0" type="metho"> <SectionTitle> 2 Linguistic motivation </SectionTitle> <Paragraph position="0"> There are a number of factors commonly acknowledged to play an important role in expressing a given content in a specific linear form.</Paragraph> <Paragraph position="1"> The inventory of these factors contains at least the following: information structure, syntactic structure, intonation, rhythm and style. Crosslinguistically, these factors may be involved in constraining linear ordering to varying degrees.</Paragraph> <Paragraph position="2"> English, for instance, is an example of a language in which WO is rather rigid, i.e., strongly constrained by syntactic structure. In such languages, differences in information structure are often reflected by varying the intonation pattern or by the choice of particular types of grammatical constructions, such as clefting and pseudo-clefting, or definiteness/indefiniteness of the nominal group. Czech, in contrast, which has a rich case system and no definite or indefinite article, belongs to the so-called &quot;free word order&quot; languages, where the same effects are achieved by varying WO. Finally, German lies between English and Czech in the spectrum between fixed and free WO. We illustrate the general point that WO selections are related to information structure by appropriateness judgements of some examples of instructions in Czech, German and English.1 Open a file with the Open command.</Paragraph> <Paragraph position="3"> The ordering in (1) is neutral in that no particular contextual constraints hold with respect to the newsworthiness of any of the elements expressed in this clause. This kind of ordering can Czech and the German examples use indicative mood as the most common way of conveying instructions of the discussed type. Alternatively, both Czech and German can use also imperatives or infinitives for instructions, but these are considered less polite than the indicative versions. Last but not least, instructions can also be formulated in indicative mood with passive voice in both Czech and German.</Paragraph> <Paragraph position="4"> be elicited by the question What should we do?.2 We follow Prague School accounts (Firbas, 1992; Sgall et al., 1986) in calling this neutral ordering the systemic ordering (cf. also a5 5). Alternatively, (1) could be used in a context characterized by the question What should we open by the Open command?, when the Open command is not being contrasted with some other entity.</Paragraph> <Paragraph position="5"> &quot;Open the file with the Open command.&quot; The word order variants illustrated in (2) and (3) are appropriate when some file is active in the context (Chafe, 1976), for instance when the user is working with a file. In (2), the action of opening is also active; in (3) it can, but does not have to be active, too. The contexts in which (2) and (3) can be appropriately used can be characterized by the questions What should we do with the file? or How should we open the file?. Unlike (2), example (3) can be used if file is contrasted with another entity. In German, this contrast is required, whereas in Czech it is optional. In English, intonation could mark whether contrast is required.</Paragraph> <Paragraph position="6"> file.</Paragraph> <Paragraph position="7"> With the Open command, open the file.</Paragraph> <Paragraph position="8"> 2We use questions for presentational purposes to indicate which contexts would be appropriate for uttering sentences with particular WO variants. Such question-answer pairs are known as question tests (Sgall et al., 1986).</Paragraph> <Paragraph position="9"> The contexts in which (4) can be used are characterized by What should we do with the Open command?. While (4) does not refer to a specific file, in (5) an activated file is presumed. (5) is appropriate in contexts characterized by What should we do to the file with theOpencommand?.</Paragraph> <Paragraph position="10"> It is also possible to use (4) in a context characterized by What should we do?, and (5) in a context characterized by What should we do to the file?, if it is presumed that we are talking about using various commands (or various means or instruments) to do various things. In the latter type of context, the Open command does not have to be activated.</Paragraph> <Paragraph position="11"> Open the file with the Open command.</Paragraph> <Paragraph position="12"> Example (6) is like (5) in that it is appropriate when both a file and the Open command are activated. The contexts in which (6) can be appropriately used can be characterized by What should we do to the file with the Open command?. Unlike (5), (6) can also be used when file is contrasted with another entity. In German, there is no difference in word order between (6) and (3) (they differ only in intonation). This is a result of the strong ordering constraint in German to place the finite verb as second (in independent, declarative clauses). In Czech verb secondness also plays a role, but it is much weaker.</Paragraph> <Paragraph position="13"> Analogous judgements concerning contextual appropriateness apply to WO variants in different mood and/or voice (when available in the individual languages). The orders in which the verb is first do not presume the activation of either a file or a command. The orders in which 'file' precedes the verb appear to presume an active file, the orders in which 'command' precedes the verb appear to presume the activation of a command. When both 'file' and 'command' precede the verb, the activation of both a file and a command appears to be presumed.</Paragraph> <Paragraph position="14"> These judgements show that differences in WO (in languages with a more flexible WO then English, e.g., Czech and German) very often correspond to differences in how the speaker presents the information status of the entities and processes that are referred to in a text, in particular, whether they are assumed to be already familiar or not, and whether they are assumed to be activated in the context. Note that in English, the same distinction is expressed by the use of a definite vs. an indefinite nominal expression, i.e.</Paragraph> <Paragraph position="15"> 'aa6 the file'.</Paragraph> <Paragraph position="16"> To summarize: Since sentences which differ only in WO (and not in the syntactic realizations of clause elements) are not freely interchangable in a given context, we have to be able to generate contextually appropriate WOs. In order to achieve this, we need to be able to capture not only the structural restrictions specific to individual languages, but also the restrictions reflecting the information status of the entities (and processes) being referred to.</Paragraph> </Section> <Section position="4" start_page="0" end_page="0" type="metho"> <SectionTitle> 3 Underlying notions </SectionTitle> <Paragraph position="0"> In order to provide constraints for WO decisions within our generation architecture, we require mechanisms through which particular patterns of information structuring can constrain the choice among the WO variants available. These patterns are provided by our text planning component. We have found two complementary approaches to the relationship between aspects of information structuring and WO to be ripe for application in the generation of extended texts; these approaches are briefly introduced below.</Paragraph> <Paragraph position="1"> In order to clarify the complementary nature of the approaches that we have adopted, it is necessary first to distinguish between two dimensions of organization that are often confused or whose difference is contested: in his Systemic Functional Grammar (SFG), (Halliday, 1970; Halliday, 1985) distinguishes between the thematic structure of a clause and its information structure: Whereas the Theme is &quot;the starting point for the message, it is the ground from which the clause is taking off&quot; (Halliday, 1985, 38), information structure concerns the distinction between the Given as &quot;what is presented as being already known to the listener&quot; (Halliday, 1985, 59), and the New as &quot;what the listener is being invited to attend to as new, or unexpected, or important&quot; (ibid).</Paragraph> <Section position="1" start_page="0" end_page="0" type="sub_section"> <SectionTitle> 3.1 Information structure and ordering </SectionTitle> <Paragraph position="0"> In Halliday's original approach (Halliday, 1967), the basic assumption for English and also for other languages is that ordering, apart from being grammatically constrained, is iconic with respect to &quot;newsworthiness&quot;. So on a scale from Given to New information, the &quot;newer&quot; elements would come towards the end of the information unit, the &quot;newest&quot; element bearing the nuclear stress. This approach relies on the possibility of giving a complete ordering of all clause elements with respect to their newsworthiness.</Paragraph> <Paragraph position="1"> The notion of ordering by newsworthiness in Halliday's approach is parallel to the notion of communicative dynamism (CD) introduced in the early works of Firbas (for a recent formulation see (Firbas, 1992)) and used also within the Functional Generative Description (FGD, (Sgall et al., 1986)). Also from the viewpoint of CD, the prototypical ordering of clause elements from left to right respects newsworthiness: In prototypical cases, WO corresponds to CD. However, textually motivated thematization or grammatical constraints may force WO to diverge from CD.</Paragraph> <Paragraph position="2"> The FGD approach differs from Halliday's in that, in addition to CD, it works with a default (canonical) ordering, called systemic ordering (SO). SO is the language specific canonical ordering of clause elements (complements and adjuncts), as well as of elements of lower syntactic levels, with respect to one another.</Paragraph> <Paragraph position="3"> For the current purposes we concentrate on the SO for a subset of the clause elements that are discerned in FGD. We use the following SOs for the Slavonic languages and for English and German:3 a mixture of FGD and SFG terminology.</Paragraph> <Paragraph position="4"> The SO for the Slavonic languages is based on the one for Czech (Sgall et al., 1986); the only difference is that we have placed Patient before Source ('from where'). We follow (Sgall et al., 1986) in considering the SOs for the main types of complementations in Russian and Bulgarian to be similar to the Czech one, though there can be slight differences (cf. the observations reported in (Adonova et al. 1999)). The SO for English combines the suggestions made by (Sgall et al., 1986) and the ordering defaults of the NIGEL grammar of English (cf. Section 5.2). The SO for German is based on (Heidolph et al., 1981, p.704).</Paragraph> <Paragraph position="5"> The informational status of elements is established through deviation of CD from the SO. This leads us to the distinction FGD makes between contextually bound (CB) and contextually non-bound (NB) items in a sentence (Sgall et al., 1986). A CB item is assumed to convey some content that bears on the preceding discourse context. It may refer to an entity already explicitly referred to in the discourse, or an &quot;implicitly evoked&quot; entity. At each level of syntactic structure, CB items are ranked lower than NB items in the CD ordering. The motivation behind and the meaning of the CB/NB distinction in FGD corresponds to those underlying the Given/New dichotomy in SFG.</Paragraph> <Paragraph position="6"> Contextual boundness can be used to constrain WO (at the clause level) as follows: a8 The CB elements (if there are any) typically precede the NB elements.</Paragraph> <Paragraph position="7"> a8 The mutual ordering of multiple CB items in a clause corresponds to communicative dynamism, and the mutual ordering of multiple NB items in a clause follows the SO (with the exceptions required by grammatically constrained ordering as described below). The default for communicative dynamism is SO.</Paragraph> <Paragraph position="8"> a8 The main verb of a clause is ordered at the boundary between the CB elements and the NB elements, unless the grammar specifies otherwise (verb secondness).</Paragraph> <Paragraph position="9"> It is the above abstract ordering principles that underly the algorithm we present in a5 5.</Paragraph> </Section> <Section position="2" start_page="0" end_page="0" type="sub_section"> <SectionTitle> 3.2 Thematic structure </SectionTitle> <Paragraph position="0"> In all languages we looked at so far, there are also orders we cannot explain solely on the basis of the CB/NB distinction along with SO and grammatical constraints. On the one hand, it has been claimed that the ordering of CB elements follows CD rather than SO, and that CD is determined by contextual factors (Sgall et al., 1986). On the other hand, cases where an NB element appears at the beginning of a clause are far from rare. While we currently do not have more to add to the former issue, the latter can be readily addressed using the notion of Theme. For illustration, consider (8) in Czech, German and English, appearing in a context where it is preceded only by (7).</Paragraph> <Paragraph position="1"> (7) First open the Multiline styles dialog box using one of the following methods.</Paragraph> <Paragraph position="2"> (8) Z The preceding context does not refer to the 'Data menu' or make it active in any way. Working only with the notion of information structure discerning CB (Given) and NB (New) elements, one is thus unable to explain this ordering. On the other hand, the notion of thematic structure as a reflection of a global text organization strategy makes such explanation possible. In Halliday's approach, Theme has a particular textual function, that of signposting the intended development or &quot;scaffolding&quot; that a writer employs for structuring an extended text. In software instruction manuals, for example, we encounter regular thematization of (i) the location where actions are performed, (ii) the particular action that the user is instructed to perform, or (iii) the goal that the user wants to achieve (cf. (Kruijff-Korbayov'a et al., in prep) for a more detailed discussion).</Paragraph> </Section> </Section> <Section position="5" start_page="0" end_page="0" type="metho"> <SectionTitle> 4 Information structure and strategic </SectionTitle> <Paragraph position="0"> planning In this section we briefly describe how we integrate information structure into strategic gen- null where (and how) content might be aggregated syntactically (e.g. conjunction) or discursively (e.g. RST-relations). In the example above, the text plan specifies a text consisting of an overall goal (the title) and five substeps to resolve that goal (the tasks). The first task is a simple one, the second task is a complex formed around an RST-purpose relation, after which follows a conjunction of tasks. (The CONJOINED-INSTRUCTION-TASKS nodes indicate that the left-daughter node (a task) and the task dominated by the immediate non-terminal node above a CONJOINED-INSTRUCTION-TASKS node, are to be related by a conjunction.) The content to be realized is identified by the leaves of the text plan. Whenever a leaf is introduced in the text plan, the discourse model is updated with the content's (A-box) concepts. The sentence planner decends through the text plan depth-first. Thereby it gathers the leaves' content into sentence-specifications, following any indications of aggregation. It makes use of the discourse model to specify whether content should be realized as contextually bound (or not). principle idea is that during text-planning, a discourse model is built that is then used in sentenceplanning to determine a sentence's information structure.</Paragraph> <Paragraph position="1"> We have developed a system using KPML. In KPML, generation resources are divided into interacting modules called regions. For the purpose of text-planning we have constructed a region that defines an additional level of linguistic resources for the level of genre. The region facilitates the composition of text structures in a way that is very similar to the way the lexico-grammar builds up grammatical structures. This enables us to have a close interaction between global level text generation and lexico-grammatical expression, with the possibility to accommodate and propagate constraints on output realization. While constructing a text plan, the text planner constructs a (rudimentary) discourse model that keeps track of the discourse entities introduced.</Paragraph> <Paragraph position="2"> Text planning results in a text plan and a discourse model that serve as input to the sentence planner. The text plan is a hierarchical structure, organizing the content into a more linear fashion (see Figure 3.2). The sentence planner creates the input to the tactical generation phase as formulas of the Sentence planning Language (SPL, (Kasper, 1989)). The SPL formulas express the bits of content identified by the text plan's leaves, and can also group one or more leaves together (aggregation) depending on decisions taken by the text planner concerning discourse relations.</Paragraph> <Paragraph position="3"> Most importantly, during this phase of planning what content is to be realized by a sentence, the underlying information structure of that content is determined: Whenever the sentence planner encounters a piece of content that the discourse model notes as previously used, it marks the corresponding item in the SPL formula as contextually bound (note that we are hereby making a simplifying assumption that in the current version of the sentence planner we equate contextual boundness with previous mention).</Paragraph> <Paragraph position="4"> The text planner can also choose a particular textual organization and determine the element which should become the Theme. If no particular element is chosen as the Theme, the grammar chooses some element as the default Theme. This can be the Subject (as in English), the least communicatively dynamic element (as in Czech); the choice of the default Theme in German is freer than in English, but more restricted than in Czech (cf. (Steiner and Ramm, 1995) for a discussion).</Paragraph> <Paragraph position="5"> The Theme is then placed at the beginning of the clause, although not necessarily at the very first position, as this might be occupied, e.g., by a connective. The placement of the Theme is also resolved by the grammar.</Paragraph> <Paragraph position="6"> 5 Realizing information structure through linearization It is in the setting described in a5 4 that the issue of generating contextually appropriate sentences really arises. In this section we describe the word ordering algorithm (a5 5.1) and its application to Czech and English (a5 5.2).</Paragraph> <Section position="1" start_page="0" end_page="0" type="sub_section"> <SectionTitle> 5.1 Flexible word order algorithm </SectionTitle> <Paragraph position="0"> As discussed, constraints from various sources need to be combined in order to determine grammatically well-formed and contextually appropriate WO. Contextual boundness is used to constrain WO at the clause level as specified above.</Paragraph> <Paragraph position="1"> We combine the following two phases in which information structure (CB/NB) is taken into account during tactical generation: a8 information structure can determine particular realization choices made in the grammar; for example, when inserting and placing the particle of a phrasal verb, when inserting and ordering the Source and Destination for a motion process; a8 information structure can determine the ordering of elements whose placement has not been sufficiently constrained by the grammar. null For a multilingual resource, this allows each language to establish its own balance between the two phases. To show our approach in a nutshell, we present an abstract WO algorithm in Figure 2.</Paragraph> <Paragraph position="2"> Given: a set GC of ordering constraints imposed by the grammar a list L1 of constituents that are to be ordered, a list D giving ordering of CB constituents (default is SO) Create two lists LC and LN of default orders: Create empty lists LC (for CB items) and LN (for NB items) Repeat for each element E in L1 if E is CB, then add E into LC, else add E into LN.</Paragraph> <Paragraph position="3"> Order all elements in LC according to D Order all elements in LN according to SO if the Verb is yet unordered then Order the Verb at the beginning of LN Order the elements of L1 if GC is not empty then use the contraints in GC, and if the contraints in GC are insufficient, apply first the default orders in LC and then those in LN The ordering constraints posed by the grammar have the highest priority. Note that this includes the ordering of the textually determined Theme. Then, elements which are not ordered by the grammar are subject to the ordering according to information structure, i.e. systemic ordering in combination with the CB/NB distinction. The ordering of the NB elements (i) is restricted by the syntactic structure or (ii) follows SO. The ordering of the CB elements can be (i) specified on the basis of the context, (ii) restricted by the syntactic structure, or (iii) follow SO.</Paragraph> <Paragraph position="4"> The ordering algorithm as such is not language specific, and could be usefully applied in the generation of any language. What differs across languages is first of all the extent to which the grammar of a particular language constrains ordering, i.e. which elements are subject to ordering requirements posed by the syntactic structure, and which elements can be ordered according to information structure. Also, it is desirable (and our algorithm allows it) to specify different systemic orderings for different languages. And, even within a single language, our algorithm allows the specification of different systemic orderings in different grammatical contexts (just by adding a realization statement that (partially) defines the SO during strategic generation).</Paragraph> <Paragraph position="5"> The algorithm is applicable in platforms other than KPML. In the first place, any grammar can modify its decisions to take information structure into account. In addition, those tactical generators allows multiple sources of ordering constraints, e.g., a combination of grammardetermined choices and defaults, as long as such that the default ordering based on information structure can be applied.</Paragraph> </Section> <Section position="2" start_page="0" end_page="0" type="sub_section"> <SectionTitle> 5.2 Algorithm application </SectionTitle> <Paragraph position="0"> The algorithm described above has been implemented and used for generation of Czech and English instructional texts. The Czech grammar resources used in tactical generation have been built up along with Bulgarian and Russian grammar resources as described in (Kruijff et al., 2000), reusing the NIGEL grammar for English. The original NIGEL grammar itself already combines the specification of ordering constraints in the grammar with the application of defaults. If an ordering is underspecified by the grammar, the defaults are applied. The defaults are &quot;static&quot;, i.e. specified once and for all. The algorithm we have described replaces these &quot;static&quot; defaults with a &quot;dynamic&quot; construction of ordering constraints. Two separate sets of &quot;dynamic&quot; defaults are computed on the basis of the SO for the CB and the NB elements in each sentence/clause.</Paragraph> <Paragraph position="1"> We use the SOs for Czech and English specified above (cf. a5 3.1). For each element in the input SPL we specify whether it is CB (:contextual-boundness yes) or NB (:contextual-boundness no); in addition, we can specify the textual Theme in the SPL (theme <id>). The SPL in Figure 3 illustrates this.</Paragraph> <Paragraph position="2"> Note that the information structure distinction between CB vs. NB elements on the one hand, and the informational status of referents as identifiable vs. non-identifiable on the other hand, are orthogonal. Whereas CB/NB has to do with the Czech and generated outputs speaker's presenting an element as either bearing on the context or context-affecting, identifiability reflects whether the speaker assumes the hearer to pick out the intended referent. These two dimensions are independent, though correlated (cf. the discussion of activation vs. identifiability in (Lambrecht, 1994)). What is encountered most often is the correlation of CB with identifiable and NB with non-identifiable. The correlation of NB with identifiable corresponds is found, e.g., in cases of &quot;reintroducing&quot; an element talked about before, or in cases like There is a square and a circle. Delete the circle. -in the second sentence, the same ordering would be used also in German (L&quot;oschen Sie den Kreis) and in Czech (VymaVzte kruh.).</Paragraph> <Paragraph position="3"> What is hard to find is the correlation of CB with non-identifiable, but it is the way we would analyze a dollar bill in example (9) (Gregory The CB/NB assignments can be varied to obtain different WO variants. The examples below show some of the CB/NB assignment combinations and the outputs generated using the Czech and English grammars.</Paragraph> <Paragraph position="4"> To open a file the user chooses Open in the menu with the mouse.</Paragraph> <Paragraph position="5"> As mentioned above, we preserve the notion of textual Theme. An SPL can contain a specification of a Theme, and the corresponding element is then ordered at the front of the sentence, as determined by the grammar. The WO of the rest of the sentence is determined as described.</Paragraph> <Paragraph position="6"> 4Regarding intonation: in English, there are two intonation phrases, the first containing dollar bill with a L+H* pitch accent on dollar, and the second with a H* pitch accent on pick up. In Czech and German it seems that a contrastive pitch accent on dolarovou bankovku is optional, and the rest can have neutral intonation with nuclear stress on the last word.</Paragraph> </Section> </Section> class="xml-element"></Paper>