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<H2>UNITY--Chandy and Misra's UNITY formalism</H2> |
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<P>The book <EM>Parallel Program Design: A Foundation</EM> by Chandy and Misra |
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(Addison-Wesley, 1988) presents the UNITY formalism. UNITY consists of an |
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abstract programming language of guarded assignments and a calculus for |
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reasoning about such programs. Misra's 1994 paper "A Logic for Concurrent |
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Programming" presents New UNITY, giving more elegant foundations for a more |
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general class of languages. In recent work, Chandy and Sanders have proposed |
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new methods for reasoning about systems composed of many components. |
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<P>This directory formalizes these new ideas for UNITY. The Isabelle examples |
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may seem strange to UNITY traditionalists. Hand UNITY proofs tend to be |
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written in the forwards direction, as in informal mathematics, while Isabelle |
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works best in a backwards (goal-directed) style. Programs are expressed as |
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sets of commands, where each command is a relation on states. Quantification |
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over commands using [] is easily expressed. At present, there are no examples |
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of quantification using ||. |
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<P>A UNITY assertion denotes the set of programs satisfying it, as |
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in the propositions-as-types paradigm. The resulting style is readable if |
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unconventional. |
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<P> Safety proofs (invariants) are often proved automatically. Progress |
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proofs involving ENSURES can sometimes be proved automatically. The |
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level of automation appears to be about the same as in HOL-UNITY by Flemming |
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Andersen et al. |
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<P> |
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The directory <A HREF="Simple/"><CODE>Simple</CODE></A> |
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presents a few examples, mostly taken from Misra's 1994 |
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paper, involving single programs. |
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The directory <A HREF="Comp/"><CODE>Comp</CODE></A> |
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presents examples of proofs involving program composition. |
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<ADDRESS> |
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<A NAME="lcp@cl.cam.ac.uk" HREF="mailto:lcp@cl.cam.ac.uk">lcp@cl.cam.ac.uk</A> |
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</ADDRESS> |
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