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samenvatting - symbol systems
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Summary of “Symbols and Search” by Newell & Simon (1976). About physical symbol systems and how they are used in AI.
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3 – Symbols and Search – Newell & Simon (1976)Auteurs: computer science is een empirische wetenschap.
• Wat bedoelen de auteurs als ze zeggen dat computer science een empirische
wetenschap is? En wat zou computer science dan zijn als het geen empirische
wetenschap was?
• De auteurs beargumenteren dat physical symbol systems de noodzakelijke en voldoende
voorwaarden hebben om intelligent gedrag te vertonen. Hoe beargumenteren ze dit? En
wat zijn physical symbol systems?
• De auteurs beargumenterendat intelligente systemen altijd heuristic search gebruiken
om problemen op te lossen. Hoe beargumenteren ze dit, en wat is heuristic search?
The authors:
- constributed to AI by: developing heuristic programming, heuristic search, means-ends
analysis, methods of induction.
- in psychology: human cognition can be described in terms of a symbol system, using computer
programs to simulate human behavior.
- they invented list processing, were contributors to the development of the concept of the
computer as a system of manipulating symbolic structures.
- computer science is an empirical discipline.
- purpose is to examine the development of new basic understanding by empirical inquiry.
Two examples:
1. the development of the notion of a symbolic system.
2. the development of the notion of heuristic search.
→ both have significance for understanding how information is processed and how intelligence is
achieved.
Symbols and physical symbol systems
- explanation of symbols is a scientific proposition about nature and is empirically derived.
- symbols lie at the root of intelligent action, which is the primary topic of AI.
- measure intelligence of a system by its ability to achieve states ends in the face of variations,
difficulties and complexities posed by the task environment.
, - laws of qualitative structure: short, general statements about the essential nature of systems,
they often set the terms on which a whole science operates. (basisprincipes van een veld)
→ cell doctrine in biology: states that the basic building block of all living organisms is the cell.
→ plate tectonics in geology: is highly qualitative.
→ germ theory of disease: identify a disease, then look for the germ; identify a task domain
calling for intelligence, then construct a program for a digital computer that can handle tasks in
that domain.
physical symbol systems:
obey the laws of physics, not restricted to human symbol systems
consists of a set of entities (symbols) which are physical patterns that occur as
components of another type of entity called an expression (or symbol structure)
composed of a number of instances (or tokens) of symbols related in some physical way
also contains processes that operate on expressions to produce other expressions:
processes of creation, modification, reproduction and destruction
machine that produces through time an evolving collection of symbol structures
→ designation: an expression designates an object if the system can either affect the object
itself or behave in ways dependent on the object (obtaining access to the object via the
expression)
→ interpretation: the system can interpret an expression if it designates a process and if the
system can carry out the process (the system can evoke and execute its own processes from
expressions that designate them)
- a system capable of designation and interpretation must also meet these requirements:
1. a symbol may be used to designate any expression whatsoever
2. there exist expressions that designate every process of which the machine is capable
3. there exist processes for creating and modifying any expression in arbitrary ways
4. expressions are stable; once created they will exist until modified or deleted
5. the number of expressions that the system can hold is essentially unbounded
The physical symbol system hypothesis:
a physical symbol system has the necessary and sufficient means for general intelligent action.
→ necessary: any system that exhibits general intelligence will prove upon analysis to be a
physical symbol system
→ sufficient: any physical symbol system of sufficient size can be organized further to exhibit
general intelligence
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