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<?xml version="1.0" standalone="yes"?> <Paper uid="J79-1082"> <Title>American Journal of Computational Linguistics Microfiche 82 A MODEL FOR KNOWLEDGE AND ITS APPLICATION TO DISCOURSE ANALYSIS</Title> <Section position="5" start_page="72" end_page="72" type="metho"> <SectionTitle> IMPLEMENTATION </SectionTitle> <Paragraph position="0"> In thiq section the imple~nentation of the structures and processes presented above is described* The original program was written in SNOBOL for a CDC6400.</Paragraph> <Paragraph position="1"> In a complete system there should, of course, be a parser. For the present this does not exist; the system only embodies the cognitive component. This means that the overall organization is not as it would be in a complete text analysis system, where interaction between the syptac tic and semantic components is essential (Woods, 1971; Schank, 1975a; Winograd, 1971; Erdman, 1975) The justification for this ommission is that for the present I am seeking to establish only the nature of the semantic organization of a coherent discourse. Once this structure has been identified it will provide the goal for a complete systern-Input to the spcern is accordingly in a cognipive form that retains the logital ellipsis of the surface form.</Paragraph> <Paragraph position="2"> Most of the processin8 is performed by &quot;Nonnalizer&quot; which infers omitted logical and thema~ic structure. A judgement of coherence is then a simple task: if the discourse is not logically connected or does not have a single theme, then it is incoherent; otherwise the matrix theme indEcates the topic of the discourse.</Paragraph> <Paragraph position="3"> A component of all processes is a breadth first path-tracing routine, called &quot;Ripple&quot;. A search path is defined by a sequence of arc types A path does not explicitly state whether an arc can be repeated. The network is assumed to be syntactically well-formed and this controls repetitions. An arc can be marked as obligatory; otherwise it is optional. A goal of the search can be defined. This may be a particular node, or a node marked with a specified &quot;activation tag&quot;, i .e., a node reached by another path, when seeking an intersection. Paradipiatic path,-tracinq Paradigmatic path-tracing is implemented by Ripple with a path sequence VAR IST TYP MAN (see Figure 11). A converse paradigmatic path ---is 'EfAN TYP IST VAR. The properties associated with a varietal concept may be found by Ripple with a path TYP MAN starting from the concept. Causal connectivity condition This process uses Ripple with cause as the path definition* It also has to include P-W arid P-W to be able to reach from and to conj unc ts.</Paragraph> <Paragraph position="4"> Discovery - of gener a1 - and spec if ic propo si ti ons All propositions of a discourse must match general propositions in the encyclopedia. The procedure is to make cyclic calls of Ripple. The first is from the modality node of the discourse proposition. Each node reached, other than the modality, initiates another search in the encyclopedia. For example, given the discourse and encyclopedia of Figure 12, the process is as follows : from &quot;gobblef' node 1, a converse paradigmatic path plus a typical arc plus manifestation ia followed to, for example, node 2 in the encyclopedia.</Paragraph> <Paragraph position="5"> Ripplipg from &quot;gobble&quot; in the If discourse gives nodes &quot;Marv&quot; and caviar&quot;. The syntagmatic arcs traversed are noted. From &quot;Marv&quot;, node A, a converse paradigmatic path plus typical plus manifestation plus converse agent is followed, with a goal of a node activated from the prior discourse node, i ~e., &quot;gobble&quot;. [Not all of these arcs have to be present, they are optional except PS0, tt the syntagmatic arc.] Node 2 satisfies this goal. From caviar&quot; node B, a converse paradigmatic path plus typical plus manifestation plus converse objective is followed with a g~al of a node activated from the prior discourse node &quot;gobbleff* Again node 2 satisfies the goal. Thus the proposition at 2 is a generalization of tihe discourse proposition. The condition on an acceptable generalized match is that it must contain all the syntagmatic informirtion of the discourse proposition,; the generalizatdon may contain more information but it cannot contain less Separate searches are made for syntagmetic structure and for spa tio-temporal information on the modality of a proposition.</Paragraph> <Paragraph position="6"> It is only necessary to change the path description from that used in Figure 12 from converse paradigmatic path to paradigmatic path for the routine to local e more specific propositions.</Paragraph> <Paragraph position="7"> kietalingual decomposition The search for general propositions also flags nodes that have metalingual definitions. New propositions having the structure of the definiens are made by copying the definiens but with node names drawn from the proposition that is being paraphrased These new propositions are then considered as part of the discourse. To make the copy, the bresdth first search routine is used to pass through the definiens. For each ode and arc in the definition, an equivalent structure is created The end of scanning a proposition of the definiens is marked by reaching a typical arc, i.e., at the point at which the definition is linked into paradigmatic organization. If a participant in the generalized proposition matches a participant in the discourse proposition then this participant fits into the corresponding role slot in the definiendum, otherwise the concept in the definiendm is used. For example, given &quot;Peter buys a bicycle from Jane&quot; and the definition of &quot;buy&quot; as in rigure 16. In locating the systemic definiendm, the correspondences of &quot;~eter&quot; to &quot;A&quot;, etc ., are also found. When copying reaches the node that matched &quot;peter&quot;, this name is inserted into the t 1 paraphrase. There is no correspondence for the instrument, so money&quot; 1s the inserted from the definiiendum, MetaLin~ual abstraction In searching for general propositions, some may be found that are components of metalingual definitions. These have modalities that are pdinted to by a part-whole arc.</Paragraph> <Paragraph position="8"> -60-The proqess that tests coreference and contextual requirements uses Ripple to traverse in parallel the candidate discourse propositions and those of the definiens. Typical arcs in the definiens limit the search. Each node of the definiens is compared with equivalent nodes in the discourse propositions at each step. A proposition is rejected if a node has no equivalent or it does not possess all the properties of the nodes of the definiens, including arcs to nodes matched in the previous step, See., if nodes x (systemic) and Y (discourse) were taken as corresponding nodes at one step, then if on the next step a node of the definition has an arc to X then the discourse must have the same arc to Ya Only those propositions that match the definiens will not have been rejected and can be rewritten using the abstrwt term. The process can -be illustrated using the definition of &quot;poison&quot; given in Figure 14b, and its application to the discourse in Figure 14a. The crux of the test is at that node of the definition having the two manifestations arcs emanating from it* If the discourse proposition did not have two manifestations it would be rejected This is how &quot;John's eating the worms made Fred sick&quot; is eliminated* Or if it does have two manifestations, they must point to nodes that were satisfied Qn the previous step of the comparison. Thus if one of the manifestations pointed into another proposition the test would fail.</Paragraph> <Paragraph position="9"> Inference I of omitted discursive relations A search along discursive arcs in systemic memory from counterparts of discourse propositions may lend to a proposition that is flagged as a generaliz~tion of another discourse proposl tion. If this is so then the discusive arc may be added between the discourse propositions. If the proposition reached is not flagged then it and the discursive arc are copied, and added to the discourse. Ttle copying routine was given in the discussion of decomposition.</Paragraph> <Paragraph position="10"> The System The flow chart of the analysts fs shown in Figure 21. The meanings of the annotations are: OLDINFO has a discourse proposition as its argument. It finds systemic equivalents. It calls a routine SPACETIME to cornpare spatio-temporal contexts. SPACETLME is also called during the search for general propositions when a non-event node is found with an attached modality. If OLDINFO is presented with a modality that has only part-whole relations ta other nodes, it does nothing.</Paragraph> <Paragraph position="11"> LOGCON has a systemic proposition as its argumfnt. It succeeds if it finds d link to a general proposition corresponding to a proposition of the discourse (including propositions added by inference). It also generates INTERLIST, a list of causal inferences from propositions of the discourse.</Paragraph> <Paragraph position="12"> IKST is a list of nodes found to have metalingual definitions.</Paragraph> <Paragraph position="13"> CONJLIST is a list of conjoined propositions. When a discourse proposition is matched against the encyclopedia, it sees if the encycl opedic proposition is a constituent of another modality. A CONJUNCTION TEST routine uses CONJLIST to locate discourse propositions that can be grouped.</Paragraph> <Paragraph position="14"> TRANSFORM has two modes . In one it is used to decompose propositions that contain a metalingually defiries concept* A second mode c eates causally inferred propositions .</Paragraph> </Section> <Section position="6" start_page="72" end_page="72" type="metho"> <SectionTitle> nNALYSIS OF SOME STORIES </SectionTitle> <Paragraph position="0"> I want to show that abstract patterns are quite general, that all linguistic behavior is based on such patterns. Obviously such a claim must be substantiated by the discovery of such patterns. A number of stories of drowning were used to test this hypothesis. The second claim of proper embedding,of themes was also tested by a more complex drowning story.</Paragraph> <Paragraph position="1"> In the examples a refined hypo thesis of discourse connectedness is used. One habit in discourse is to set the stage (kropp's &quot;Initial Situation&quot;, ~on~acre's &quot;Aperture&quot;). In terms of the model thin aspect should be recognizable by the occurrence of space and time relations.</Paragraph> <Paragraph position="2"> ?I We find todayf', &quot;in MB resevoir&quot;, &quot;On October 11, 1974&quot;. &quot;DF of Quekns&quot;, etc. A greater stru~tural complexity of expression is to be expected elsewhere in the stories (see Longacre's comments on nuclear tagmemes, above). Longacre (1972) includes in the nmural outline of a discourse, recognition of a peak within the discourse. Various surface markings for the peak are given: tense change, extra long sentences, rhetorical underlinings, etc. Taking an ethnocentric view of the world (cf. White's teleogical commune), it is suggested that In the underlying form, the peak will lie within causally related propositions. It is thus expected to find the theme within the causal structure and so I focus on this organization. This would be inappropriate if the stories were aescriptions of the kind elicited by Linde, above.</Paragraph> <Paragraph position="3"> Common patterns Shart factual accounts of drowning8 were elicited from freshmen fn Linguistics and English. The instructions given sought only to define a topic and an approleimate length: &quot;Write a drowning story that, for example, you might expect to find as a column filler in the New York Times.&quot; A sample is (Story 1) The body of Horatio Smith was found last night in the Niagar a River He was drowned when his boat overturned on the river .</Paragraph> <Paragraph position="4"> The hypothesis formed is that an acceptable drowning story must give the following information: (a) Why the victim was in the water.</Paragraph> <Paragraph position="5"> (b) Why the victim was not able to save himself The rationales for these requisites are: (c) A person is not usually found in water, and therefore some explanation of this location is expected.</Paragraph> <Paragraph position="6"> (d) By an instinct of self-preservation, one would expect the victim to try to extricate himself from his predicament.</Paragraph> <Paragraph position="7"> The story should say why he couldn't.</Paragraph> <Paragraph position="8"> Figure 22 shows the cognitive form of this requirement.</Paragraph> <Paragraph position="9"> The empty modalities indicate that a matching story must have something that stand in a causal relationship to the other propositions, Lee, explain why they happened (what caused them) If not originally explicit, this information must be recoverable through encyclopedic knowledge.</Paragraph> <Paragraph position="10"> One way in which the content of systemic memory may be substantiated is by examination of negative propositions in the stories; writers presumably only need to negate normal expectancies, and this is what generalizations are. Unfortunately there are few negatives in the stories. Stories 31 and 5 indicate the assumption of swimming ability. Stories 12, 32, and 42 show that the success of rescue attempts is anticipated.</Paragraph> <Paragraph position="11"> -66-The stories elicited fell into several categories. The two analysed here are a boat capsizing and a fall into water. In spite of surface difference it will be shown that: at an abstract level the stories conforn to the thematic pattern. The analysis of one story from each category is presented Stories not analysed include such happenings as a person eating too much then going for a swim; Jesus freaks trang to walk on water; and water-skiers having accidents while watching bikini-clad occupants of passing boats A boat capsizing -(Story 1) The body of Horatio Smith was found last night in the Niagara River He was drowned when his boat over turned in the river.</Paragraph> <Paragraph position="12"> (Story 2) Eggbert Willis, 56, of Bayside, drowned this morning after the boat he was rowing overturned near Devil's Cove. (Story 3) The body of John Smith, 58, was discovered today at the foot of West Ferry Street* He was reported missing four days ago by his wife after he failed to return from a boating trip. HIS boat had capsized. Death was due to drowning.</Paragraph> <Paragraph position="13"> (Story 31) A small sailboat was afloat on a calm peaceful lake when suddenly the mast of the vessel struck some cables overhead and the boat capsized. The two Inen aboard drowned, ane because he was hit by the boat and rendered unconscious, the other didn't know how to swim* Story 1 is analysed* In it, some of the causal and thematic structure is absent and is reconstructed using the following knowledge: (i) If a person is in a boat and the boat overturns, this may cause him to be injured and to be in the water.</Paragraph> <Paragraph position="14"> (ii) If injured a person may not be able to act&quot;.</Paragraph> <Paragraph position="15"> (iii) If a person is in water and cannot &quot;act&quot; then he may drown. The nodes appearing in the encyclopedic entries for all of these Eacts exemplified in this aection are linked to varietal nodes by typical arcs. This is so because the Eacts qre not obligatory on some concept but are something that may happen to some examples of this category some of the time.</Paragraph> <Paragraph position="16"> In the analysis of the collection of drowning stories, only the parts of the story that are relevant to the dtowning are conside'ted. For example, in Story 1, only the second sentence is processed; the first deals with an event after the death and c~sequently is excluded. The result of the analysis is shown in Fip;ure 23. The original propositions of the discourse are: Boat contains Horatio Smith Boat overturns &quot;on Niagara River.</Paragraph> <Paragraph position="17"> Horatio Smith drowns.</Paragraph> <Paragraph position="18"> The antecedent conditions expressed in a general form in (i) match the specific situation in Story 1. Thus it is inferred that Moratio Smith is in the water and that he is injured. From (if) it follows that he is not: able to act. By being in the water and not able to act, he can drown, a fact stated explicitly in the story, as shown in Figure 23- null hrther we have explanations for Horatio Smith being in the water: the boat he was in ovexturned; and for him not being able to act: he was in j ur ed . The theme fits. We have a connected discourse with (trivially) a single-rooted theme; it is coherent. The possibility that a boat over turning only puts a person into the water is added to the encyclopedia to account for part of Story 31, where it is not an injury but the inability to swim that prevents one victim from saving himself. This has consequences for Story 1. These two facts match the same propositions but are an exclusive conjunction. When an complex is found that has the same constituents, as an conjunction already cow structed, the later episode is stacked and used if the current analysis path fails* In Story 1 the use of the alternative does not lead to a connected structure. The subsequent backup then takes the correct A fall into water I--The second category of dromina story requires the addition of the knowledge that &quot;If a person falls, he may injure himselftta Ten stories in this category are listed below.</Paragraph> <Paragraph position="19"> (StoPy 5) Early titis morning, James R. Smith, age 7, was for~nd In a swimming pool near liis hame. Investigators say the boy stumbled into the pool in the darkness esrly this morning whilst looking for his pet kitten, Unable to swim, the boy drowned.</Paragraph> <Paragraph position="20"> (Story 7) At the home of blrs. ~ohn Smith on Elmwood Avenue, a boy,. Mark, age 15, drowned in his pool. The boy was with two other friends. They were performing water stunts when Mark fell and smashed his head on the bottom of the pool (Story 12) Yesterday afternoon, the life of a Buffalo youth was taken when he slipped on rocks- at a local quarry. The failure of attempted rescues resulted in the drowning of llichael Smith, age 7, of 29 Oak Street, Buffalo.</Paragraph> <Paragraph position="21"> (Story 19) A 12 year-old boy was found drowned in Ellicott Creek. Sources say the boy ran away from home and fell accidentally into the water.</Paragraph> <Paragraph position="22"> (Story 26) -A l0-yea1 dd boy died last night when he fell into a smkl pond. His friends say he was chasing his parakeet which had escaped from its cage, when the incident occurred.</Paragraph> <Paragraph position="23"> (Story 32)- Steve Smith, of Hickstown, drowned today while sailing on Glasslyke Eake. EIr . Smith, who was knocked- overboard when struck * on the head by 8 seagull, perished ,before help could reach him. His son Edgar's attempts to save his life proved futile. (Story 37) hn unidentified man was seen by several persons fa;lingsinto the Niagara River at the foot oE Ferry Street. He was later pulled from the water and pronounced dead at the scene. The cause of death was drowning.</Paragraph> <Paragraph position="24"> (Story 38) Today, the world's greatest swimmer died. John Whale was preparing to take a bath when he tripped and fell into the bath Cause of death was# drowning.</Paragraph> <Paragraph position="25"> -70(Story 40) On October llth, 1974, an unidentified man drowned in his bathtub at the Hotel Sheraton* The drowning was due to the fact that h6 fell into the tub in trying to make himself sobet. (Story 42) An 11 year-old boy drowned today after falling into the canal where he and his friends were playing. The two other boys, both eleven, tried to save their companion but were unable to do so* (Story 4) A body was found early yesterday at the foot of the Mango River, near Clubsport* The body is believed to be that of Jose Gepasto. It seems as if Mr Gepaeto's car made a wrong turn on the highway and plunged into the water Story 4 is analysed* Note that it does not explicitly mention the motion of the person, only that of the car. Understanding the story requires that it be known that: (h) If a person is &quot;contained&quot; by something that falls, then he also falls.</Paragraph> <Paragraph position="26"> (b) If a person is &quot;contained&quot; by something that is in contact with something (emgm, water), then the person is in contact with the something (water) too.</Paragraph> <Paragraph position="27"> (But not if the something is a submariner) Further it is not given that Jose Gepasto drowns. This can be inferred, but the inference chain is open ended. The analysis continued making causal inferefices and conjunctive groupings, some of which led to the discovery of the theme* Only when the system ran out of logical and conjunctive possibilities, did it make the ccannec tedness test. Embedded themes Story 22, in fact taken from the New York Times, looks like a drowning story, and as shall be shown, does contain this theme. However, it contains more. The claim i&quot;s made that it is a &quot;tragedyt'. (Story 22) DF, 43 years old, of Queens, drowned today in MB resevoir after rescuing his son D, who had fal,lem into the water while on a fishing trip at TF, near here, the police said. This theme is defined in Figure 6 as a situation in which &quot;Someane does a good act [e.g., rescue) and dies (e.g., drowns)&quot;. It will be seen that the tragedy is a proper sub theme of the drowning theme. Thus, though the story may be edid to have two themes, one is part of the other, and by our hypothesis, the discourse is still coherent. At each step the encyclopedic knowledge used in the inference and an outline of the inferred nodes are indicated Figure 25 shows an outline of the evolved atruc ture, where the original discourse propositions are shown by and inferfed proposi tiona by 0.</Paragraph> <Paragraph position="28"> To rescue someone who is in the water, get into the water. (Nodes 8, 9) Step 5. Acting causes weariness. (Node 10).</Paragraph> <Paragraph position="29"> Step 6. Weariness causes inability to act. (Node 11).</Paragraph> <Paragraph position="30"> Step 7. In water and not able to act causes drowning.</Paragraph> <Paragraph position="31"> (Node 12 and a link to node 4).</Paragraph> <Paragraph position="32"> Note that the antcedent condition in Step 3 is the same as in Step 7. Both resultant situations are possible and are noted The system can select either. However, the wrong choice does not lead to a connected structure and backup to the alternative has to be made. After Step 7 the discourse has an inferred caugal structure connec ting all the original propositions.</Paragraph> <Paragraph position="33"> The theme &quot;tragedy&quot; fits, the rescue is a (partial) cause of the demisem Rescue is a variety of act and good can apply to it and Brown is a variety of die. The drowning theme is also present.</Paragraph> <Paragraph position="34"> Although the drowning theme is not defined in terms of the tragedy, it can be seen that one is properly embedded in the other. The Process that performed the analysis is at present incomplete because the notion of embedding is nQt well understood for the highly structured network. The process used the transitivity of cause and the conj oining of propositions . Thus Che tragedy encompasses propositions 3, 10, 11, and 4 and the drowning 8, 9, 10, 11, and 4. The transitivity of cause lets the chain 3, 10, 11 be equivalent to the chain 10 and 11.</Paragraph> <Paragraph position="35"> A postmorrem on this example reveals a serious flaw. As can be seen the rescue is the cause of the father being in the water The analysis has failed to dietinguish desire for an action, a goal, from the execution of the action. A more satisfying analysis would include some of the mechanisms to be found in the robot planner of Furugori C4975). Step 2 should be seen as setting up the conditions for the son to drown, which is an event that should be prevented.</Paragraph> <Paragraph position="36"> This provides a goal for the subsequent activities . One way to prevent someone from drowning is to save him, this is a subgoal that would directly achieve the goal. If you want to rescue someone who is in the water, then it may be necessary to get into the water. With this subgoal included, the goal can be achieved, and the analysis resumes at Step 5. Figure 26 shows this preferred analysis of this fragment of the story. This would not c'hange the relative status of the themes.</Paragraph> </Section> class="xml-element"></Paper>