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3.5.3.3. Conceptual Approaches: The Narrative Knowledge Representation Language While the Conceptual Graphs theory is presented by Sowa as a tool for representing, in general, the semantics of natural languages, Zarri's NKRL (Narrative Knowledge Representation Language) has a less ambitious goal. NKRL is aimed, in fact, at proposing some possible, pragmatic solutions for the set-up of a standardized description of the semantic contents (the "meaning") of a specific class of NL texts, the "narrative documents." With the term "narrative documents," NKRL denotes NL texts of a particular industrial and economic interest corresponding, e.g., to news stories, corporate documents, normative texts, intelligence messages, etc. NKRL is a two-layer language. The lower layer consists of a set of general tools that are structured into several integrated components, four in this case. The descriptive component concerns the tools used to produce the formal representations (called predicative templates) of general classes of narrative events, like "moving a generic object," "formulate a need," "be present somewhere." Predicative templates are characterized by a threefold format, where the central piece is a semantic predicate (a primitive, like BEHAVE, EXPERIENCE, MOVE, PRODUCE, etc.) whose arguments (role fillers) are introduced by such roles as SUBJ(ect), OBJ(ect), SOURCE, DEST(ination), etc.; the data structures proper to the descriptive component are then similar to the case-grammar structures. Templates are structured into a hierarchy, H_TEMP(lates), corresponding, therefore, to a "taxonomy of events." Templates' instances (predicative occurrences), i.e., the NKRL representation of single, specific events, like "Tomorrow, I will move the wardrobe," "Lucy was looking for a taxi," "Peter lives in Paris," are in the domain of the factual component. The definitional component supplies the NKRL representations, called concepts, of all the general notions, like physical_entity, human_being, taxi_, city_, etc., that can play the role of arguments within the data structures of the two components above. The concepts correspond to sets or collections, organized according to a generalization/specialization (tangled) hierarchy which, for historical reasons, is called H_CLASS(es). The data structures used for the concepts are, substantially, frame-like structures; H_CLASS corresponds relatively well, therefore, to the usual ontologies of terms. [([slashed Lambda]x) [ELEPHANT: *x] <-- (AGNT) <-- [PERFORM] --> (IN) --> [CIRCUS]: {*}] - (BENF) <-- [EARN] --> (PTNT) --> [MONEY]. FIGURE 17 A [slashed Lambda]-expression used to define a "single-use" concept. The enumerative component of NKRL concerns the formal representation of the instances (concrete, countable examples, see lucy_, wardrobe_1, taxi_53) of the concepts of H_CLASS; their formal representations take the name of individuals. In the following, we will use the italic type style to represent a "concept_," and the roman style to represent an "individual_." The upper layer of NKRL consists of two parts. The first is a "catalog," giving a complete description of the formal characteristics and the modalities of use of the well-formed, "basic templates" (like "moving a generic object" mentioned above) associated with the language -- presently, about 150, pertaining mainly to a (very general) socio-economico-political context where the main characters are human beings or social bodies. By means of proper specialization operations, it is then possible to obtain, from the basic templates, the (specific) "derived" templates that could be concretely needed to implement a particular, practical application -- e.g., "move an industrial process" -- and the corresponding occurrences. In NKRL, the set of legal, basic templates can be considered, at least in a first approach, as fixed. Analogously, the general concepts that pertain to the upper levels of H_CLASS -- such as human_being, physical_entity, modality_, etc. -- form a type of upper-level, invariable ontology. Figure 18 supplies a simple example of NKRL code. It translates a small fragment of news story: "Milan, October 15, 1993. The financial daily Il Sole 24 Ore reported Mediobanca had called a special board meeting concerning plans for capital increase." In this figure, c1 and c2 are symbolic labels of occurrences; MOVE and PRODUCE are predicates; SUBJ, OBJ, TOPIC ("à propos of...") are roles. With respect to the arguments, sole_24_ore, milan_, mediobanca_ (an Italian merchant bank), summoning_1, etc. are individuals; financial_daily, special_, cardinality_, and several_ (this last belonging, like some_, all_ etc., to the logical_quantifier intensional subtree of H_CLASS) are concepts. The attributive operator, SPECIF(ication), with syntax (SPECIF e1 p1 ... pn), is used to represent some of the properties that can be asserted about the first element e1, concept or individual, of a SPECIF list; several_ is used within a SPECIF list having cardinality_ as first element as a standard way of representing the plural number mark (see c2). The arguments, and the templates/occurrences as a whole, may be characterized by the presence of particular codes, the determiners: e.g., the location determiners, represented as lists, are associated with the arguments (role fillers) by using the colon, ":," operator (see c1). For some information on the determiners date-1 and date-2, see Zarri (1995).
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