泛化双向相似连接

相似连接是数据管理领域的一个热门话题,已在社会生产生活中得到广泛应用.然而,现有的相似连接方法并不能满足真实世界不断增长的客观需求.本文通过引入定义在多种数据类型上的“满足”操作符和每条数据的独立阈值定义了一种新的相似连接——泛化双向相似连接.这种连接扩展了相似连接的应用范围.同时,本文还提出了两种高效的解决泛化双向相似连接问题的方法：子连接集算法和映射-过滤-验证算法.在真实和合成数据集上的大量实验结果展示了所提方法的正确性和有效性.     

Bisimilarity of Open Terms

Traditionally, in process calculi, relations over open terms, i.e., terms with free process variables, are defined as extensions of closed-term relations: two open terms are related if and only if all their closed instantiations are related. Working in the context of bisimulation, in this paper we study a different approach; we define semantic models for open terms, so-called conditional transition systems, and define bisimulation directly on those models. It turns out that this can be done in at least two different ways, one giving rise to De Simone's formal hypothesis bisimilarity and the other to a variation which we call hypothesis-preserving bisimilarity (denoted ^fh and ^hp, respectively). For open terms, we have (strict) inclusions ^fhhpci (the latter denoting the standard “closed instance” extension); for closed terms, the three coincide. Each of these relations is a congruence in the usual sense. We also give an alternative characterisation of ^hp in terms of nonconditional transitions, as substitution-closed bisimilarity (denoted ^sb). Finally, we study the issue of recursion congruence: we prove that each of the above relations is a congruence with respect to the recursion operator; however, for ^ci this result holds under more restrictive conditions than for ^fh and ^hp.     

Bisimilarity in Term Graph Rewriting

We present a survey of confluence properties of (acyclic) term graph rewriting. Results and counterexamples are given for different kinds of term graph rewriting; besides plain applications of rewrite rules, extensions with the operations of collapsing and copying, and both operations together are considered. Collapsing and copying together constitute bisimilarity of term graphs. We establish sufficient conditions for—and counterexamples to—confluence, confluence modulo bisimilarity, and the Church–Rosser property modulo bisimilarity. Moreover, we address rewriting modulo bisimilarity, that is, rewriting of bisimilarity classes of term graphs.     

Bisimilarity for the Region Calculus

A region calculus is a programming language calculus with explicit instrumentation for memory management. Every value is annotated with a region in which it is stored and regions are allocated and deallocated in a stack-like fashion. The annotations can be statically inferred by a type and effect system, making a region calculus suitable as an intermediate language for a compiler of statically typed programming languages.Although a lot of attention has been paid to type soundness properties of different flavors of region calculi, it seems that little effort has been made to develop a semantic framework. In this paper, we present a theory based on bisimulation, which serves as a coinductive proof principle for showing equivalences of polymorphically region-annotated terms. Our notion of bisimilarity is reminiscent of open bisimilarity for the -calculus and we prove it sound and complete with respect to Morris-style contextual equivalence.As an application, we formulate a syntactic equational theory, which is used elsewhere to prove the soundness of a specializer based on region inference. We use our bisimulation framework to show that the equational theory is sound with respect to contextual equivalence.     

Refining the Undecidability Border of Weak Bisimilarity

Weak bisimilarity is one of the most studied behavioural equivalences. This equivalence is undecidable for pushdown processes (PDA), process algebras (PA), and multiset automata (MSA, also known as parallel pushdown processes, PPDA). Its decidability is an open question for basic process algebras (BPA) and basic parallel processes (BPP). We move the undecidability border towards these classes by showing that the equivalence remains undecidable for weakly extended versions of BPA and BPP. In fact, we show that the weak bisimulation equivalence problem is undecidable even for normed subclasses of BPA and BPP extended with a finite constraint system.     

Bisimilarity enforcing supervisory control for deterministic specifications

This paper studies the supervisory control of nondeterministic discrete event systems to achieve a bisimulation equivalence between the controlled system and the deterministic specification. In particular, a necessary and sufficient condition is given for the existence of a bisimilarity enforcing supervisor, and a polynomial algorithm is developed to verify such a condition. When the existence condition holds, a bisimilarity enforcing supervisor is constructed. Otherwise, two methods are provided for synthesizing supremal feasible sub-specifications.     

Bisimilarity Control of Partially Observed Deterministic Systems

Control for safety and nonblockingness using a deterministic supervisor requires the specification language be controllable and observable (under the setting that marking is also decided by a supervisor). We argue that there exist cases where the above properties do not hold, yet a safe and nonblocking control can be synthesized by allowing the supervisor to be nondeterministic. Use of a nondeterministic supervisor yields a controlled system that is nondeterministic for which a language equivalence only preserve the safety but not the nonblocking property, and so instead we require the stronger equivalence of bisimilarity (which preserves "sequential" behavior such as safety as well as "branching" behavior such as nonblockingness). This motivates us to consider control of deterministic systems for achieving bisimulation equivalence to possibly nondeterministic specifications. We introduce the notions of state-achievability (SA) and state-achievability-bisimilar (SAB) as part of the existence condition, and develop effective algorithms for verify the existence conditions as well as for synthesizing a supervisor when the existence condition holds. We show that the complexity of verifying the existence of a controller is polynomial, whereas that of computing a controller (when one exists) is singly exponential. The proposed approach can be applied to enforce any property that depends on branching and sequential behavior.     

Deciding Branching Bisimilarity of Normed Context-Free Processes Is in Σ2

We show that the problem of deciding branching bisimulation equivalence for normed context-free processes is in Σ^p₂, the second level of the polynomial-time hierarchy, and hence in PSPACE. We also show that minimization of normed context-free process graphs is in PSPACE.     

互模拟准局部验证算法的扩展与实现

互模拟是并发系统的分析和验证的一个重要概念。本文主要扩展了一种由Du和Deng提出的准局部算法,使其更加适用于一般的标记迁移系统。我们用Java实现扩展后的准局部算法与Fernandez和Mounier提出的局部算法。我们以VLTS为实验数据基准,进行大量的实验,发现在大多数情况下,前者的性能比后者更好。同时,我们修改了算法使其能够验证模拟关系。最后,我们用Java实现对标记迁移系统进行转换,使算法同时可以验证弱互模拟关系。     

Deciding orthogonal bisimulation

Bergstra, Ponse and van der Zwaag introduced in 2003 the notion of orthogonal bisimulation equivalence on labeled transition systems. This equivalence is a refinement of branching bisimulation, in which consecutive tau’s (silent steps) can be compressed into one (but not zero) tau’s. The main advantage of orthogonal bisimulation is that it combines well with priorities. Here we solve the problem of deciding orthogonal bisimulation equivalence in finite (regular) labeled transition systems. Unlike as in branching bisimulation, in orthogonal bisimulation, cycles of silent steps cannot be eliminated. Hence, the algorithm of Groote and Vaandrager (1990) cannot be adapted easily. However, we show that it is still possible to decide orthogonal bisimulation with the same complexity as that of Groote and Vaandrager’s algorithm. Thus if n is the number of states, and m the number of transitions then it takes O(n(m + n)) time to decide orthogonal bisimilarity on finite labeled transition systems, using O(m + n) space. J. Parrow     

Complexity of Weak Bisimilarity and Regularity for BPA and BPP

It is an open problem whether weak bisimilarity is decidable for Basic Process Algebra (BPA) and Basic Parallel Processes (BPP). A PSPACE lower bound for BPA and NP lower bound for BPP have been demonstrated by Stribrna. Mayr achieved recently a result, saying that weak bisimilarity for BPP is Π^p₂-hard. We improve this lower bound to PSPACE, moreover for the restricted class of normed BPP.Weak regularity (finiteness) of BPA and BPP is not known to be decidable either. In the case of BPP there is a Π^p₂-hardness result by Mayr, which we improve to PSPACE. No lower bound has previously been established for BPA. We demonstrate DP-hardness, which in particular implies both NP and co-NP-hardness.In each of the bisimulation/regularity problems we consider also the classes of normed processes.Note: full version of the paper appears as [18].     

Complexity of Weak Bisimilarity and Regularity for BPA and BPP

It is an open problem whether weak bisimilarity is decidable for Basic Process Algebra (BPA) and Basic Parallel Processes (BPP). A PSPACE lower bound for BPA and NP lower bound for BPP have been demonstrated by Stribrna. Mayr achieved recently a result, saying that weak bisimilarity for BPP is Π^p₂-hard. We improve this lower bound to PSPACE, moreover for the restricted class of normed BPP.Weak regularity (finiteness) of BPA and BPP is not known to be decidable either. In the case of BPP there is a Π^p₂-hardness result by Mayr, which we improve to PSPACE. No lower bound has previously been established for BPA. We demonstrate DP-hardness, which in particular implies both NP and co-NP-hardness.In each of the bisimulation/regularity problems we consider also the classes of normed processes.Note: full version of the paper appears as [18].     

A Small Model Theorem for Bisimilarity Control Under Partial Observation

This paper extends our prior result on decidability of bisimulation equivalence control from the setting of complete observations to that of partial observations. Besides being control compatible, the supervisor must now also be observation compatible. We show that the "small model theorem" remains valid by showing that a control and observation compatible supervisor exists if and only if it exists over a certain finite state space, namely the power set of the Cartesian product of the system and the specification state spaces. Note to Practitioners-Non-determinism in discrete-event systems arises due to abstraction and/or unmodeled dynamics. This paper addresses the issue of control of non-deterministic systems subject to non-deterministic specifications, under a partial observation of events. Non-deterministic plant and specification are useful when designing a system at a higher level of abstraction so that lower level details of the system and its specification are omitted to obtain higher level models that are non-deterministic. The control goal is to ensure that the controlled system has an equivalent behavior as the specification system, where the notion of equivalence used is that of bisimilarity. Bisimilarity requires the existence of an equivalence relation between the states of the two systems so that transitions on common events beginning from a pair of equivalent states end up in a pair of equivalent successor states. Supervisors are also allowed to be nondeterministic, where the nondeterminism in control is implemented by selecting control actions nondeterministically from among a set of precomputed choices. The main contribution of this paper is to show that a supervisor exists if and only if one exists where the size of its state-space upper bounded and so it suffices to search over this state space. We illustrate our results through a manufacturing example     

Deciding co-observability is PSPACE-complete

In this note, we reduce the deterministic finite-state automata intersection problem to the problem of deciding co-observability for regular languages using a polynomial-time many-one mapping. This demonstrates that the problem of deciding co-observability for languages marked by deterministic finite-state automata is PSPACE-complete. We use a similar reduction to reduce the deterministic finite-state automata intersection problem to deciding other versions of co-observability introduced in a previous paper. These results imply that the co-observability of regular languages most likely cannot be decided in polynomial time unless we make further restrictions on the languages. These results also show that deciding decentralized supervisor existence is PSPACE-complete and therefore probably intractable.     

Deciding Global Partial-Order Properties

Model checking of asynchronous systems is traditionally based on the interleaving model, where an execution is modeled by a total order between atomic events. Recently, the use of partial order semantics, representing the causal order between events, is becoming popular. This paper considers the model checking problem for partial-order temporal logics. Solutions to this problem exist for partial order logics over local states. For the more general global logics that are interpreted over global states, only undecidability results have been proved. In this paper, we present a decision procedure for a partial order temporal logic over global states. We also sharpen the undecidability results by showing that a single until operator is sufficient for undecidability.A preliminary version of this paper appears in Proceedings of the 25th International Colloquium on Automata, Languages, and Programming (ICALP98), LNCS 1443, pp. 41–52, 1998.     

Operational semantics of Framed Tempura

This paper investigates the operational semantics of temporal logic programs. To this end, a temporal logic programming language called Framed Tempura is employed. The evaluation rules for both the arithmetic and boolean expressions are defined. The semantic equivalence rules for the reduction of a program within a state is formalized. Furthermore, the transition rules within a state and transition rules over an interval between configurations are also specified. Moreover, some examples are given to illustrate how these rules work. Thus, the executable behavior of framed programs can be captured in an operational way. In addition, the consistency between the operational semantics and the minimal model semantics based on model theory is proved in detail.