Concurrent MetateM

Concurrent MetateM is a multi-agent language in which each agent is programmed using a set of (augmented) temporal logic specifications of the behaviour it should exhibit. These specifications are executed directly to generate the behaviour of the agent. As a result, there is no risk of invalidating the logic as with systems where logical specification must first be translated to a lower-level implementation.

The root of the MetateM concept is Gabbay's separation theorem; any arbitrary temporal logic formula can be rewritten in a logically equivalent past → future form. Execution proceeds by a process of continually matching rules against a history, and firing those rules when antecedents are satisfied. Any instantiated future-time consequents become commitments which must subsequently be satisfied, iteratively generating a model for the formula made up of the program rules.

Temporal Connectives

The Temporal Connectives of Concurrent MetateM can divided into two categories, as follows:

• Strict past time connectives: '●' (weak last), '◎' (strong last), '◆' (was), '■' (heretofore), 'S' (since), and 'Z' (zince, or weak since).

• Present and future time connectives: '◯' (next), '◇' (sometime), '□' (always), 'U' (until), and 'W' (unless).

The connectives {◎,●,◆,■,◯,◇,□} are unary; the remainder are binary.

Strict past time connectives

Weak last

●ρ is satisfied now if ρ was true in the previous time. If ●ρ is interpreted at the beginning of time, it is satisfied despite there being no actual previous time. Hence "weak" last.

Strong last

◎ρ is satisfied now if ρ was true in the previous time. If ◎ρ is interpreted at the beginning of time, it is not satisfied because there is no actual previous time. Hence "strong" last.

Was

◆ρ is satisfied now if ρ was true in any previous moment in time.

Heretofore

■ρ is satisfied now if ρ was true in every previous moment in time.

Since

ρSψ is satisfied now if ψ is true at any previous moment and ρ is true at every moment after that moment.

Zince, or weak since

ρZψ is satisfied now if (ψ is true at any previous moment and ρ is true at every moment after that moment) OR ψ has not happened in the past.

Present and future time connectives

Next

◯ρ is satisfied now if ρ is true in the next moment in time.

Sometime

◇ρ is satisfied now if ρ is true now or in any future moment in time.

Always

□ρ is satisfied now if ρ is true now and in every future moment in time.

Until

ρUψ is satisfied now if ψ is true at any future moment and ρ is true at every moment prior.

Unless

ρWψ is satisfied now if (ψ is true at any future moment and ρ is true at every moment prior) OR ψ does not happen in the future.

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