the knowledge level: structure and details (a. newell, 1982)

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The Knowledge Level: Structure and Details

Newell, A. (1982). The knowledge level. Artificial intelligence, 18(1), 87-127.

Anna Fensel

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11.05.2016

• Knowledge Level Structure• Knowledge Level Details

Outline

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“I am about to propose the existence of something called the knowledge level, within which knowledge is to be defined. I am about to propose the existence of something called the knowledge level,within which knowledge is to be defined.”

What it is about?


First, from computer system levels…


A level can be defined either autonomously, without reference to another level, or with a reference to a level under it.

Aspects of a computer system level…


All levels share some common features…


• Each computer system level is a specialization of the class of systems capable of being described at the next lower layer…

• Computer system levels are realized by technologies…• They are approximations…• Non-completeness and no full interoperability (e.g. common at device

level) – and we live with it…• No descriptions of the environment around the level ever available…

Computer system levels are a reflection of the nature of the physical world, as:


• The system at the knowledge level is the agent. • The components at the knowledge level are goals, actions, and

bodies. • Thus, an agent is composed of a set of actions, a set of goals and a

body. • The medium at the knowledge level is knowledge (as might be

suspected). • Thus, the agent processes its knowledge to determine the actions to

take. • Finally, the behavior law is the principle of rationality: Actions are

selected to attain the agent's goals.– E.g. if you know that 2+2 is 4, you rationally reply “4” on a question “how

much is 2+2”, if it is your goal to give a correct answer.

Knowledge level is a systems level, like all the other system levels


Knowledge Level Introduction


• The structure, consisting of the system, components and laws for composing systems;

• the laws of behavior (the law of rationality); • the medium (knowledge).

After this we will describe how the knowledge level reduces to the symbol level.

Details of Knowledge Level


• Agent: – has some physical body and a set of actions. These can be arbitrary

complex, and are external to the knowledge level.– has a body of knowledge. Acts like a memory, has constraints w.r.t. its

structure, size, etc.– has set of goals. A goal is a body of knowledge of a state of affairs in the

environment, formed out of body of knowledge of the agent.

• No structures for an agent, no ways to build complex agents.

The structure


No straightforward way to predict the actions, e.g. goals and actions can be physically unattainable, contradicting each other, knowledge can be incomplete, etc.

Principle of rationality


• Knowledge. Whatever can be ascribed to an agent, such that its behavior can be computed according to the principle of rationality.– Designed functionally, not structurally.

• Knowledge of the world cannot be captured in a finite structure. E.g. even when playing chess, a human cannot predict the situation on the board after X steps.

The nature of knowledge


• Knowledge, in the principle of rationality, is defined entirely in terms of the environment of the agent, for it is the environment that is the object of the agent's goals, and whose features therefore bear on the way actions can attain goals.

• A logic is just a representation of knowledge. It is not the knowledge itself, but a structure at the symbol level.

• The knowledge level is only an approximation, and a relatively poor one on many occasions--we called it radically incomplete.

• An essential part of the current proposal is the existence of the second level of approximation, namely, the symbol level.

• Fundamental principle of the observer: “To ascribe to an agent the structure S is to ascribe whatever the observer can know from structure S.”

Solutions to the representation of knowledge


• Knowledge, the medium at the knowledge level, corresponds at the symbol level to data structures plus the processes that extract from these structures the knowledge they contain.

Relation of the knowledge level to the symbol level


• Knowledge level and its details are introduced.– Principle of rationality– The nature of knowledge – Knowledge representation

• If an actual system is produced, all knowledge-level descriptions must ultimately be replaced by symbol-level descriptions.

• The knowledge-level description can be a good approximation even though the subsystem being so described is quite simple, due to the nature of the goals and environments of such agents, whose specification is also under the control of the system designer.

Conclusions


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the knowledge level: structure and details (a. newell, 1982)

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