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Conceptual Representation and ScriptingRecall a famous story, perhaps the birth of Jesus, "Boy Cries Wolf", "Little Red Riding Hood" or any story that you know. Now, tell that story to a friend. After that, tell that story to another friend. Did you tell the story in the exact same way each time? It is highly likely you didn't. Why did you do this? The answer lies in the way you remember the story - you do not remember the story word for word, you store the ideas and the concepts of the story in your head. In Artificial Intelligence, this is called conceptual representation (CR).
Applications of CRWhat does this have to do with Artificial Intelligence? Well, imagine the potential of a program that could parse information and store it in a string of concepts. Here are just a few applications that CR can be applied to:
CR Structures (CRS)After giving you three examples of how CR can be used, it makes you wonder why such programs aren't out yet. Creating a successful CR program is incredibly difficult. Let's look at one possible CRS. This CRS was devised at Yale for, as they put it, "possesion-changing-actions". They named it ATRANS, Abstract TRANSfer of Possesion. The example I am going to give is a very simple one — for more complicated diagrams, see Does the Top-Down or Bottom-Up Approach Best Model the Human Brain.Basically, a CRS (like ATRANS) represents a very simple action, a base action that many other actions can be made up of. ATRANS can be used to represent give, trade, buy, exchange, sell and many, many more. Structurally, a CR is a series of 'slots', or expectations, that the computer fills as its parses and interprets the sentence. Input: "John sold Mary a book" Through the representation that would be created inferences such as these could be created:
ScriptingHow does the program about create such inferences? I said that it uses prior knowledge - this prior knowledge will often come in the form of a script. Schank describes a script like this:"...Scripts are prepackaged set of expectations, inferences, and knowledge that are applied in common situations, like a blueprint for action without the detail filled in..."Scripts are used by humans, in a sense. Imagine you hear this story: "Bob went to the shops. Ten minutes later, he walked out with his shopping and went home." You make a few assumptions - that Bob bought the shopping, that Bob was short of a few items etc. The reason you know this is because you follow a script unconciously in your head. You know the basic outline of shopping (due to experience) and you can fill in the details, and make assumptions from the rest. Let's look at another story: "Bob went to the gardeners. He asked the waiter for a BMW and left." Now, this story makes no sense whatsoever to the normal person! This is because is does not follow the "gardeners-script". Gardeners don't have waiters, nor do they sell BMWs!
Example of a Script.Here is an incredibly simple example of a script, based on how to turn on a computer:
CR ProgramsHaving said that CR programs are incredibly difficult to program, that doesn't mean such programs don't exist. All have been demonstration, proof-of-concept programs. I will look at two - one called SAM and another called IPP.SAMPerhaps one of the most famous AI programs, SAM (Script Applier Mechanism) was developed in 1975 by Richard Cullingford, Wendy Lehnert, Anatole Gershman and Jaime Carbonell. It was designed to read stories that followed basic scripts, and output summaries in several languages, and create questions and answers based on the text.SAM had 4 basic modules: a parser and generator based on a previous program, then the main module - the Script Applier (by Cullingford), the question-answer module (Lehnert), and the Russian and Spanish generators (Gershman and Carbonell, respectively).
Here is some sample output from SAM:
SAM had a few shortcomings, though. If a story digressed from a script, SAM would have a hard time. A program that handled stories with more complicated plots, and characters would need more complicated structures. Five years and several programs later, IPP was developed. IPPIPP was developed in 1980 by Michael Lebowitz. IPP used slightly more advanced techniques than SAM -- in addition it to CR primitives and scripts it used plans and goals too (beyond the scope of this essay). IPP was built to look at newpaper articles of a specific domain, and to make generalizations about the information it read and remembered. IPP was important because it could update and expand its own memory structures.
Here is some sample output from the program, reading articles about Basque terrorism:
This program obviously had its limitations. Often the conclusions it made were a little deceptive, and the domain was limited. Nevertheless this program was a definite landmark in CR programs. Other CR programs included MARGIE, PAM, POLITICS, FRUMP, BORIS and the very impressive CYRUS. To find more information on these programs, refer to pgs 138-163 in Schank's Cognitive Computer.
Addendum: Problems with Conceptual RepresentationThis essay in its original form was one of the first I wrote for Generation5. I had the early AI researcher enthusiasm - since then, I have become rather disenchanted with the entire top-down approach to Artificial Intelligence. (For readers unsure about the concepts of 'top-down' and 'bottom-up' I'll refer you to Does the Top-down or the Bottom-Up Approach More Closely Model the Brain - the essay I wrote that started the whole disillusionment process!)As I explained above, the problems with natural language processing as a whole are huge. Conceptual Representation is no exception to any of these. Imagine coding what we know as 'commonsense' into computer code? In fact, a project is on-going in Texas called the Cyc Project. After 14 years, they have a million or so facts down in computable form. While this is impressive - even more impressive will be the search algorithm to go through them! I think that while the goals of the Cyc Project are genuine, once finished (if ever) it will be of little use to anyone. The lack of discourse knowledge is just one problem (albeit the biggest). Other areas of critique are the huge amount of domain knowledge required on top of 'commonsense'. The lack of biological plausibility is another - structures manipulated in a serial fashion is not how the brain works. The serial fashion of processing has another problem - speed! Now, I believe that natural language processing will be one of the last (if not THE last) field of Artificial Intelligence to fully mature. Robots such as Cog may one day be able to come up with methods of learning language by themselves, without having to be explictly taught. This is the goal of robotics after all - implicit learning.
Last Updated: 13/12/1999 Article content copyright © James Matthews, 1999.
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