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This format is interpreted as follows: |
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IF condition 1 is satisfied (in this case, by a message, on the message list, that
starts with 1),
AND condition 2 is satisfied (in this case, by a second, specific, message
001001),
"THEN the message in the action part (in this case, 000011) is posted to the
message list on the next time-step. |
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Conditions may be negated: For example, -1##### is satisfied if there is no message on the message list that begins with a 1. With these provisions it is easy to show that a classifier system is computationally complete, in the sense that any program that can be written in a standard programming language, such as Fortran, C, or Lisp, can be implemented within a classifier system. |
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Without any changes to this definition, rules can be given an "address" that can be used by other rules when that is useful. Consider a rule r with a condition of the form 111# . . . #. Any message that starts with three 1s will satisfy this condition. If this particular prefix, 111, is reserved for the rule r alone, then any message with that prefix will be directed to r and only to r. Such reserved prefixes (they can also be suffixes, or indeed any part of the message) are called tags.Of course, several rules might have the same reserved tag; that simply means that all of them receive messages so tagged, acting as a cluster with respect to that tag. Appropriate use of tags also permits rules to be coupled to act sequentially. |
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The basic execution cycle of the classifier system consists of an iteration of the following steps: |
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1. Messages from the environment are placed on the message list. |
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2. Each condition of each classifier is checked against the message list to see if it is satisfied by (at least one) message thereon. |
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3. All classifiers that have both conditions satisfied participate in a competition (to be discussed in a moment), and those that win post their messages to the message list. |
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4. All messages directed to effectors are executed (causing actions in the environment). |
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5. All messages on the message list from the previous cycle are erased (i.e., messages persist for only a single cycle, unless they are repeatedly posted). |
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Because the message list can hold an arbitrary number of messages, any number of rules can be active simultaneously; because the messages are simply uninterpreted |
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