一个框架时序逻辑程序设计语言

_______________________________________________________________________________
A Framed Temporal Logic Programming Language
Zhenhua Duan Computer School Xidian U niversity Xi an 710071 P.R.China zhhduan@ Maciej Koutny Department of Computing Science U niversity of N ewcastle upon T yne N ewcastle upon T yne N E 1 7RU, U.K. M aciej.Koutny @
1
_______________________________________________________________________________ 中国科技论文在线

2
interval over which it is executed. In particular, the sequence of processes, p1 , . . . , pm and process q may terminate at different time points. Although the communication between processes is still based on shared variables, the communication and synchronization only take place at the rendezvous points (global states), otherwise they are executed independently. The new projection operator also enables the specification of program execution using different time scales. Another problem that must be dealt with in temporal logic programming is that of communication between concurrent processes. Some models of concurrency involve shared (programming) variables, some involve synchronous message passing (e.g. CCS [8] and CSP [9]), and some involve asynchronous channels. In temporal logic programming languages, such as XYZ/E [5, 6], Tempura [4], METAMET [1] and TOKIO [2], the communication between parallel components is based on shared variables. Similarly as many concurrent programming languages [10], to synchronize communication between parallel processes in a concurrent program with the shared variable model (e.g., when solving the mutual exclusion problem), a synchronization construct, await(c) or some equivalent is required. The meaning of await(c) is simple: it changes no variables, but waits until the condition c becomes true, at which point it terminates. In a sequential program, an await statement is useless, since if c is currently false it will remain so forever. However, within a concurrent program this statement makes perfect sense since another process, acting in parallel, may cause c to become true. Defining await(c) is difficult without some kind of a framing construct. However, there is a problem which is caused by the fact that in temporal logic the values of variables are not inherited automatically from one state to another. Yet, to implement await(c), one requires some kind of indefinite stability, since one cannot know at the point of use how long the waiting will last. At the same time one must also allow variables to change, so that an external process can modify the Boolean parameter and it can eventually become true. Framing is concerned with how the value of a variable can be carried from one state to the next. In [11], a framing technique in temporal logic programming was introduced by means of an explicit operator, frame(x). The new construct was interpreted within minimal model semantics. This allows one to specify the framing status of variables throughout an interval in a flexible manner, and to define await(c) in an easy way. It should be noted that introducing the framing operator destroys the monotonicity and leads to a default logic [12]–[14]. Therefore, negation by default has to be used to manipulate the framing operator. In this paper, we formalize a framed concurrent temporal logic programming language, FTLL, under the projection temporal logic framework, PTL, a variant of interval temporal logic. An interpreter [11], written in SICSTUS Prolog, has been developed for a subset of FTLL using the framing technique presented here. The paper is organized as follows. The next section presents some fundamental aspects of the underlying PTL logic. In Section 3, the framing technique is discussed. Section 4 describes the framed programming language FTLL, and Section 5 provides two examples of FTLL programs. Conclusions are drawn in Section 6.
∗ Support by the National Natural Science Foundation of China under Grant No.60373103, the SRFDP Grant 20030701015 and the Grant SYSKF0407 from Lab. Computer Science, ISCAS.
∗
Abstract We discuss the projection temporal logic (PTL), based on a primitive projection operator, prj . A framing technique is also presented, using which a synchronization operator, await, is defined within the underlying logic. A framed temporal logic programming language (FTLL) is presented. To illustrate how to use both the language and framing technique, some examples are given. Keywords: Temporal logic, Temporal logic programming, Frame, Projection, Concurrency