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<Paper uid="T75-2023">
  <Title>TAKE (X) PTRANS (X to B) $CONT $LINK,$UNIT MTRANS (ATRANS? X to B) to Y DECIDE ON PLAN Does Y want something? Fear something? Am I honest? BARGAIN INFORM STEAL THREATEN TRADE ASK OVER- POWER</Title>
  <Section position="1" start_page="0" end_page="118" type="abstr">
    <SectionTitle>
USING KNOWLEDGE TO UNDERSTAND
</SectionTitle>
    <Paragraph position="0"> Minsky's frames paper has created quite a stir within AI but it is not entirely clear that any given researcher who would agree that the frames approach is correct would agree with any other researcher's conception of what exactly that meant. What is a frame anyway? It has been apparent to researchers within the domain of natural language understanding for some time that the eventual limit to our solution of that problem would be our ability to characterize world knowledge. In order to build a real understanding system it will be necessary to organize the knowledge that facilitates understanding. We view the process of understanding as the fitting in of new information into a previously organized view of the world. Thus we would extend our previous view of language analysis (Schank \[1973\] and Riesbeck \[1974\]) to the problem of understanding in general. That is, a language processor is bottom up until it gets enough information to enable it to make predictions and become top down. Input sentences (like input words in intra-sentence analysis) set up expectations about what is likely to follow in the text.</Paragraph>
    <Paragraph position="1"> These expectations arise from the world knowledge that pertains to a given situation, and it is these expectations that we wish to explore here.</Paragraph>
    <Paragraph position="2"> We choose to call our version of frames, SCRIPTS. The concept of a script, as we shall use it here, is a structure that is made up of slots and requirements on what can fill those slots. The structure is an interconnected whole, and what is in one slot affects what can be in another. The entire structure is a unit that describes a situation as a whole and makes sense to the user of that script, in this case the language understander.</Paragraph>
    <Paragraph position="3"> A script is a predetermined sequence of actions that define a situation. Scripts are responsible for, and can be recognized by, the fact that they allow for references to objects within them Just as if that object had been mentioned before. That is, certain objects within a script may be referenced by &amp;quot;the&amp;quot; because the script itself has implicitly introduced them.</Paragraph>
    <Paragraph position="4"> Some examples: I. John went into the restaurant.</Paragraph>
    <Paragraph position="5"> He ordered a hamburger, but he found it tasteless.</Paragraph>
    <Paragraph position="6"> He asked the waitress to yell at the chef for him.</Paragraph>
    <Paragraph position="7"> II. John got in his car.</Paragraph>
    <Paragraph position="8"> When he put the key in, he didn't hear a thing.</Paragraph>
    <Paragraph position="9"> He called the garage.</Paragraph>
    <Paragraph position="10">  In these paragraphs, what we are calling scripts play a major role. We have discussed previously (Schank \[1974\]) how paragraphs are represented as causal chains in memory. This work implies that whenever a story is understood, inferences must be made that will connect up each input conceptualizaton to those that relate to it in the story. This connecting up process is difficult and dependent upon the making of inferences to tie together seemingly unrelated pieces of text. However, it is a process that can be facilitated tremendously by the use of scripts.</Paragraph>
    <Paragraph position="11"> We define a script as a predetermined causal chain of conceptualizations that describe the normal sequence of things in a familiar situation. Thus there is a restaurant script, a birthday-party script, a football game script, a classroom script, and so on. Each script has in it a minimum number of players and objects that assume certain roles within the script. A script is written from the point of view of a player in one of these roles. Different scripts are defined when different roles are used as the focus of a situation.</Paragraph>
    <Paragraph position="12"> The following is a sketch of a script for a restaurant from the point of view of the customer: script: restaurant roles: customer; waitress; chef; cashier reason: to get food so as to go down in hunger and up in pleasure  scene I entering PTRANS - go into restaurant MBUILD - find table PTRANS - go to table MOVE - sit down scene 2 ordering ATRANS - receive menu ATTEND - look at it MBUILD - decide on order MTRANS - tell order to waitress scene 3 eating ATRANS - receive food INGEST - eat food scene 4 exiting MTRANS - ask for check ATRANS - give tip to waitress PTRANS - go to cashier ATRANS - give money to cashier PTRANS - go out of restaurant  In this script, each primitive action given stands for the most important element in a standard set of actions. The instruments for performing each action might vary with the circumstances, as might the whole act itself. For example, in scene I, the problem of finding a table might be handled by a maitre d', and if the restaurant is fancy enough this might require an ATRANS of money. These variables aside, the above script expresses the general flow of events.</Paragraph>
    <Paragraph position="13"> Within each act sequence, the principle of causal chaining (see Schank \[.1973\]) is used. That is, each action results in conditions that enable the next to occur. New information that is received from the analysis of a text is interpreted in terms of its place within one of the causal chains within the script.</Paragraph>
    <Paragraph position="14"> Thus in paragraph I, the first sentence exemplifies the first action in scene I. Sentence 2 refers to the last line of scene 2 and the last line of scene 3. In addition it provides information about the result of the INGEST in scene 3. The third sentence does not fit anywhere in the script, but rather is part of a subscript that defines complaining behavior. (Such a subscript can be called by certain scripts that deal with services rovided by an organization.) The final representation of paragraph I would contain the entire restaurant script, filled in with what was specifically stated and with assumptions about what must of been true also included (that he sat down, for example). In addition there would be a complaining script attached to the entire description at the appropriate point in the final representation.</Paragraph>
    <Paragraph position="15"> The general form for a script then is a set of paths that conjoin at certain crucial points. These crucial points serve to define the script. The paths of a script are the possibilities that are extant in a situation.</Paragraph>
    <Paragraph position="16"> A script is made up of a number of distinct parts. In order to know when a script is appropriate a set of script headers are necessary. These headers define the circumstances under which a script is called into play. Certain key words serve this purpose together with a range of contexts in which those words may or may not fit. The headers for the restaurant script are the words restaurant, diner, out to eat, and so on when mentioned in the context of a plan of action for getting fed. States such as hunger can call up the restaurant script as well. Obviously contexts must be restricted so as to not call the restaurant script for sentences which use the word restaurant only as a place (i.e., &amp;quot;Fuel oil was delivered to the restaurant.&amp;quot;) Situational scripts have crucial parts which can be said to define them. For restaurants the crucial parts are the INGEST and the ATRANS of money. All other parts have alternatives that allow for certain paths within the script to be followed while others are ignored. Thus, ordering may be done by MTRANSing to a waiter or by selecting and taking what you like (as in a cafeteria). Likewise the ATRANSing may be done by going to the cashier or paying the waitress, or saying &amp;quot;put it on my bill&amp;quot;. These variations indicate that a situational script is not a simple list of events, but rather a linked causal chain that can branch into multiple possible paths. These paths come together again at crucial defining parts of the script.</Paragraph>
    <Paragraph position="17">  We believe that the nature of human memory is episodic. By that we mean that memory is organized around past sequences of action. When certain sequences happen often enough generalized situational scripts come to be associated with the words or circumstances that set them up, as their definition. People that have not had a familiarity with a given situation cannot be expected to have a script for that situation. Children learn these scripts by repeated associations with them. We learn to make sense of the world, by organizing the knowledge that we have so as to enable us to interpret new data in terms of our expectatons. These expectations have been generated, in part, by scripts. This is really no more than saying tha a person who has never been to a football game will have no script by which he can understand the events that go on there. (There is an important human ability to generalize scripts from others of course. So if he has seen other games it will help.) Not everything one encounters in life has necessarily been seen before. On Occasion we encounter novel situations in which we must create a plan or else understand somebody @lse's plan. Consider the following: John wanted to become chief supervisor at the plant. He decided to go and get some arsenic.</Paragraph>
    <Paragraph position="18"> How are to make sense of such a paragraph? This paragraph make no use of situational words or the scripts that they denote. It would be unreasonable to posit a &amp;quot;want to be a supervisor&amp;quot; script that had all the necessary acts laid out as in our restaurant script. But, on the other hand, the situation being described is not entirely novel, either. The problem of understanding this paragraph would not be significantly different if &amp;quot;chief supervisor of theplant&amp;quot; were changed to &amp;quot;president of the men s club&amp;quot; or &amp;quot;king&amp;quot;, the similarity is that there is a general goal state that is the same in each case and a generalized plan or group of plans that may potentially lead to that goal state. One possible desired goal state is POWER. The plan in memory associated with POWER is probably fairly complex. For that reason we have chosen to deal in the initial stages with a simpler world than that of general society. We have chosen bears.</Paragraph>
    <Paragraph position="19"> Suppose you are a bear in the woods and you can talk to the other animals there and you are hungry. It is necessary to develop a plan of action that will enable you to eat. In the dullest of eases, you have always lived in the same old forest, in that forest is a bee's nest that regularly produces honey which they allow you to take. So you follow the course of action that you have used many times before and you get fed. This is a script. A script is applied whenever a course of action is laid out and need only be blindly followed in order to achieve a goal. Thus it is basically a set of knowledge associated with a given goal.</Paragraph>
    <Paragraph position="21"> But the dullest of cases is of course not the best one to learn things from. So, now suppose that you are a bear in the woods who has not been a bear in the woods before.</Paragraph>
    <Paragraph position="22"> You have no set script to follow, all you know is what you like to eat. In that case i you must develop a PLAN. In order to discuss what such a plan might look like, we must first point out that the setting down of a plan that will work is not the same as l the creation of a plan. If you use a prestored plan for getting food in the woods you have cheated. You have used a script.</Paragraph>
    <Paragraph position="23"> In creating a plan we make use of some .~ general knowledge about goals and subgoals. I Such general knowledge is made up of sequences of actions that are used to obtain certain goals. Abstract entities called PLANS are names of possible combinations of l action sequences (sort of mini-scripts) that will achieve a given goal.</Paragraph>
    <Paragraph position="24"> If you want to eat you must GET some food. This information is found by l consulting two sources. First, the desired ACT INGEST requires &amp;quot;food&amp;quot; as its object. Second, in order to do any ACT on any physical object, you must have that physical l object in proximity. The plan to do this is called GET(X), where X is the object being sought. The plan GET(X) should tell us how to obtain the needed X in a way that uses knowledge about getting things in general t before it uses knowledge about X in particular.</Paragraph>
    <Paragraph position="25"> Once it is established that GET(X) is what we want, the problem is to translate the abstract entity GET(X) into a sequence of conceptualizatons that can actually be executed. GET(X) is simply the name of a set of subplans: FIND(X) PROX(X) and i TAKE(X). FIND(X) is the name of a set of possible sequences of actions that will result in the state that will enable PROX(X) to be executed. PROX(X) stands for the l possible sets of actions that get an actor where he wants to be. In order to do that an actor must know the location of X. So when FIND(X) is done the knowledge about where to go has been detemlned. This I knowledge enables PROX(X) which tells how to get there. Now TAKE(X) can be executed.</Paragraph>
    <Paragraph position="26"> The successful completion of TAKE(X) enables the ultimate goal INGEST(X).</Paragraph>
    <Paragraph position="27"> l above entities the of The are names PLANS. PLANS are made up of desired stages and the actions that will effect them together with the cost and circumstances I surrounding the choice of a particular set at a particular time. The possible paths are called PLANBOXES. Planboxes are made up of conceptualizations that will yield i desired state changes together with the preconditions that must be satisfied in order to enact the actions in those conceptualizations.</Paragraph>
    <Paragraph position="28"> We can now examine one plan in particular. The TAKE plan is intended to enable whatever is done with an object in general, to be done at this particular time. i Consequently its eventual result is potentially different if what is to be done is physical or social. On the physical level, the result is always ATRANS which is accomplished by means of a PTRANS. The enabling conditions for the ATRANS are then simply the enabling conditions for the PTRANS. In order to PTRANS something you must be physically proximate to it, so th~ location of the object and the taker must be identical or a PTRANS to the location of the object must have previously taken place.</Paragraph>
    <Paragraph position="29"> The result of the ATRANS above is that a possession change exists. This will enable the final desired ACT to take place.</Paragraph>
    <Paragraph position="30"> The TAKE plan is concerned with eliminating any preconditions that might get in the way of the enabling PTRANS. The preconditions are that no one else has CONTROL of the object being sought or else that there are no concomitant bad consequences in the attempt to PTRANS to self. The TAKE plan simply calls a PTRANS if all the preconditions are positive. However if someone else CONTROLS the object, a plan for gaining CONTROL must be called. The rough outline of the TAKE plan is then as follows:</Paragraph>
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