4776
|
1 |
<!-- $Id$ -->
|
|
2 |
<HTML><HEAD><TITLE>HOL/UNITY/README</TITLE></HEAD><BODY>
|
|
3 |
|
|
4 |
<H2>UNITY--Chandy and Misra's UNITY formalism</H2>
|
|
5 |
|
|
6 |
<P>The book <EM>Parallel Program Design: A Foundation</EM> by Chandy and Misra
|
|
7 |
(Addison-Wesley, 1988) presents UNITY, which consists of an abstract
|
|
8 |
programming language of guarded assignments and an associated calculus.
|
|
9 |
Misra's 1994 paper "A Logic for Concurrent Programming" presents "New UNITY",
|
|
10 |
giving more elegant foundations for a more general class of languages.
|
|
11 |
|
|
12 |
<P> This directory is a preliminary formalization of New UNITY. The Isabelle
|
|
13 |
examples may not represent the most natural treatment of UNITY style. Hand
|
|
14 |
UNITY proofs tend to be written in the forwards direction, as in informal
|
|
15 |
mathematics, while Isabelle works best in a backwards (goal-directed) style.
|
|
16 |
|
|
17 |
<P>
|
|
18 |
The syntax, also, is rather unnatural. Programs are expressed as sets of
|
|
19 |
commands, where each command is a relation on states. Quantification over
|
|
20 |
commands using [] is easily expressed. At present, there are no examples of
|
|
21 |
quantification using ||.
|
|
22 |
|
|
23 |
<P>
|
|
24 |
The directory presents a few small examples, mostly taken from Misra's 1994
|
|
25 |
paper:
|
|
26 |
<UL>
|
|
27 |
<LI>common meeting time
|
|
28 |
|
|
29 |
<LI>the token ring
|
|
30 |
|
|
31 |
<LI>the communication network
|
|
32 |
|
|
33 |
<LI><EM>n</EM>-process deadlock
|
|
34 |
|
|
35 |
<LI>unordered channel
|
|
36 |
|
|
37 |
<LI>reachability in directed graphs (section 6.4 of the book)
|
|
38 |
</UL>
|
|
39 |
|
|
40 |
<P> Safety proofs (invariants) are often proved automatically. Progress
|
|
41 |
proofs involving ENSURES can sometimes be proved automatically. The
|
|
42 |
level of automation appears to be about the same as in HOL-UNITY by Flemming
|
|
43 |
Andersen et al.
|
|
44 |
|
|
45 |
<HR>
|
|
46 |
<P>Last modified on $Date$
|
|
47 |
|
|
48 |
<ADDRESS>
|
|
49 |
<A NAME="lcp@cl.cam.ac.uk" HREF="mailto:lcp@cl.cam.ac.uk">lcp@cl.cam.ac.uk</A>
|
|
50 |
</ADDRESS>
|
|
51 |
</BODY></HTML>
|