Feedback automata and their languages

We introduce families of languages which are generated by deterministic and nondeterministic feedback-controlled models of automata. In case of the two deterministic models considered, the generated families are proper subclasses of the family of regular languages, where, in case of the nondeterministic model, the generated family equals the family of ?-free regular languages.     

A computational model for tiling recognizable two-dimensional languages

Tiling systems are a well accepted model to define recognizable two-dimensional languages but they are not an effective device for recognition unless a scanning strategy for the pictures is fixed. We define a tiling automaton as a tiling system equipped with a scanning strategy and a suitable data structure. The class of languages accepted by tiling automata coincides with the REC family. In this framework it is possible to define determinism, non-determinism and unambiguity. Then (deterministic) tiling automata are compared with the other known (deterministic) automata models for two-dimensional languages.     

Decidability of operation problems for T0L languages and subclasses

We investigate the decidability of the operation problem for T0L languages and subclasses. Fix an operation on formal languages. Given languages from the family considered (0L languages, T0L languages, or their propagating variants), is the application of this operation to the given languages still a language that belongs to the same language family? Observe, that all the Lindenmayer language families in question are anti-AFLs, that is, they are not closed under homomorphisms, inverse homomorphisms, intersection with regular languages, union, concatenation, and Kleene closure. Besides these classical operations we also consider intersection and substitution, since the language families under consideration are not closed under these operations, too. We show that for all of the above mentioned language operations, except for the Kleene closure, the corresponding operation problems of 0L and T0L languages and their propagating variants are not even semidecidable. The situation changes for unary 0L languages. In this case we prove that the operation problems with respect to Kleene star, complementation, and intersection with regular sets are decidable.     

P-hardness of the emptiness problem for visibly pushdown languages

Visibly pushdown languages form a subclass of the context-free languages which is appealing because of its nice algorithmic and closure properties. Here we show that the emptiness problem for this class is not any easier than the emptiness problem for context-free languages, namely hard for deterministic polynomial time. The proof consists of a reduction from the alternating graph reachability problem.     

Deterministic Lindenmayer languages,nonterminals and homomorphisms

Lindenmayer systems are a class of parallel rewriting systems originally introduced to model the growth and development of filamentous organisms. Families of languages generated by deterministic Lindenmayer systems (i.e., those in which each string has a unique successor) are investigated. In particular, the use of nonterminals, homomorphisms, and the combination of these are studied for deterministic Lindenmayer systems using one-sided context (D1Ls) and two-sided context (D2Ls). Languages obtained from Lindenmayer systems by the use of nonterminals are called extensions. Typical results are: The closure under letter-to-letter homomorphism of the family of extensions of D1L languages is equal to the family of recursively enumerable languages, although the family of extensions of D1L languages does not even contain all regular languages. Let P denote the restriction that the system does not rewrite a letter as the empty word. The family of extensions of PD2L languages is equal to the family of languages accepted by deterministic linear bounded automata. The closure under nonerasing homomorphism of the family of extensions of PD1L languages does not even contain languages like {a₁,a₂,?, a_n}¹--{λ}, n?2 . The closure of the family of PD1L languages under homomorphisms which map a letter either to itself or to the empty word is equal to the family of recursively enumerable languages. Strict inclusion results follow from necessary conditions for a language to be in one of the considered families. By stating the results in their strongest form, the paper contains a systematic classification of the effect of nonterminals, letter-to-letter homomorphisms, nonerasing homomorphisms and homomorphisms for all the basic types of deterministic Lindenmayer systems using context.     

Parallel programming with logic languages: A survey

Formal properties of logic languages are largely studied; however, their impact on the practice of software design and programming is currently minimal. In this paper we survey some interesting representatives of the family of logic languages aiming at comparing the different capabilities they offer for designing and programming parallel systems. The logic languages Prolog, Aurora, Flat Concurrent Prolog, Parlog, GHC, and DeltaProlog were chosen, because a suitable set of relevant examples has been published, mostly by the language designers themselves. A number of sample programs is used to expose and compare the languages with respect to their object oriented programming capabilities for multiprocess coordination, interprocess communication, and resource management. Special attention is devoted also to metaprogramming as well, seen as a useful technique for specifying and building the operating environments of the languages themselves. The paper ends with a discussion on positive and negative features found comparing these languages, and indicates some guidelines to be followed in the design of new logic languages.     

赋权型自动机的不同模型研究

自动机理论是理论计算机科学的基础理论之一,在很多领域自动机有着广泛的应用,有穷状态自动机是正则语言的识别机器,通常分为确定型与非确定型两种模型,其识别语言的能力是等价的。赋权自动机是另一类重要的自动机模型,自动机的每条转移规则和状态可以赋以某一代数结构上的某一数值,从而可以计算输入字符串的权值。任何有穷状态自动机都可以视为一特殊赋权自动机,因此赋权自动机功能更强大,应用更为广泛。     

Tree Tuple Languages from the Logic Programming Point of View

We introduce inductive definitions over language expressions as a framework for specifying tree tuple languages. Inductive definitions and their subclasses correspond naturally to classes of logic programs, and operations on tree tuple languages correspond to the transformation of logic programs. We present an algorithm based on unfolding and definition introduction that is able to deal with several classes of tuple languages in a uniform way. Termination proofs for clause classes translate directly to closure properties of tuple languages, leading to new decidability and computability results for the latter.     

函数式逻辑语言的操作语义

函数式语言和逻辑语言在下列意义上是互补的,基于归约的函数式程序设计语言具有确定和懒惰求解等性质.但同时它又缺少诸如存在量化的变量以及部分数据结构等所希望的性质.相反,基于HORN子句逻辑和消解原理的逻辑程序设计语言允许存在量化的变量和部分数据结构但又缺少确定和懒惰求解的性质.从这个角度出发,把函数和逻辑程序设计语言结合成一种范型是很自然的,这种结合提供了一种比逻辑和函数语言表达能力更强的合一语言.提出了函数式逻辑语言的操作语义,同时表明这种操作语义在实践中是可见的.     

Recursive functions of context free languages (I)--The definitions of CFPRF and CFRF

It is intended to establish the recursive function theory on context free languages (CFLs). In this paper, the function class CFRF and its proper subclass CFPRF were defined on CFLs; it is quite straightforward to use them for describing non_numerical algorithms. In fact, they are respectively the partial recursive functions and primitive recursive functions of context free languages. The structure induction method for proving CFPRF function properties was presented. A method for CFL sentence enumeration was given, the minimization operator was defined. Based on CFL sentence enumeration, the minimization operator evaluation method was given. Finally, the design and implementation principles of executable specification languages with the CFRF as theoretical basis were discussed.     

Toward diagrammability and efficiency in event-sequence languages

Many industrial verification teams are developing suitable event-sequence languages for hardware verification. Such languages must be expressive, designer friendly, and hardware specific, as well as efficient to verify. While the formal verification community has formal models for assessing the efficiency of an event-sequence language, none of these models also accounts for designer friendliness. We propose an intermediate language for event sequences that addresses both concerns. The language achieves usability through a correlation to timing diagrams; its efficiency arises from its mapping into deterministic weak automata. We present the language, relate it to existing event-sequence languages, and prove its relationship to deterministic weak automata. These results indicate that timing diagrams can become more expressive while remaining more efficient for symbolic model checking than LTL.     

Recursive functions of context free languages (Ⅰ)——The definitions of CFPRF and CFRF

It is intended to establish the recursive function theory on context free languages (CFLs). In this paper, the function class CFRF and its proper subclass CFPRF were defined on CFLs; it is quite straightforward to use them for describing non-numerical algorithms. In fact, they are respectively the partial recursive functions and primitive recursive functions of context free languages. The structure induction method for proving CFPRF function properties was presented. A method for CFL sentence enumeration was given, the minimization operator was defined. Based on CFL sentence enumeration, the minimization operator evaluation method was given. Finally, the design and implementation principles of executable specification languages with the CFRF as theoretical basis were discussed.     

Parsers for indexed grammars

Three classes of parsable indexed grammars are defined. The new parsing mechanisms are derived by extending those that have been most successful for contextfree grammars, the LR and LL algorithms. Design criteria for the new grammar classes include membership decidability and unambiguity. We show that all three parsers operate in linear time for at least some grammars in our new classes. One of our new classes generates all the deterministic contextfree languages, along with some noncontextfree languages. We also show that the flag strings generated by indexed grammars are regular sets. This is done by showing that they can be generated by regular canonical systems.     

A CKY parser for picture grammars

We study the complexity of the membership or parsing problem for pictures generated by a family of picture grammars: Siromoney's Context-Free Kolam Array grammars (coincident with Matz's context-free picture grammars). We describe a new parsing algorithm, which extends the Cocke, Kasami and Younger's classical parsing technique for string languages and preserves the polynomial time complexity.     

Optimization schemas for parallel implementation of non‐deterministic languages and systems

Naive parallel implementation of non‐deterministic systems (such as a theorem proving system) and languages (such as logic, constraint, or concurrent constraint languages) can result in poor performance. We present three optimization schemas, based on flattening of the computation tree, procrastination of overheads, and sequentialization of computations that can be systematically applied to parallel implementations of non‐deterministic systems/languages to reduce the parallel overhead and to obtain improved efficiency of parallel execution. The effectiveness of these schemas is illustrated by applying them to the ACE parallel logic programming system. The performance data presented show that considerable improvement in execution efficiency can be achieved. Copyright © 2001 John Wiley & Sons, Ltd.     

Recursive functions of context free languages (I)

It is intended to establish the recursive function theory on context free languages (CFLs). In this paper, the function class CFRF and its proper subclass CFPRF were defined on CFLs; it is quite straightforward to use them for describing non-numerical algorithms. In fact, they are respectively the partial recursive functions and primitive recursive functions of context free languages. The structure induction method for proving CFPRF function properties was presented. A method for CFL sentence enumeration was given, the minimization operator was defined. Based on CFL sentence enumeration, the minimization operator evaluation method was given. Finally, the design and implementation principles of executable specification languages with the CFRF as theoretical basis were discussed. This paper is based on the Technical Report ISCAS-LCS-2k-03 (SAQ Report No. 30): Recursive Functions Defined on Context Free Languages (I), August 2000, with minor revisions.     

Some relations between Markov algorithms and formal languages

Markov algorithms have received very little attention in the studies about formal languages, so the purpose of the present paper is twofold: i) to characterize languages in terms of Markov algorithms, and ii) to produce automatically Markov algorithms accepting or parsing languages generated by given grammars. We use a particular, although universal, subclass of Markov algorithms, which we call “pointer Markov algorithms»; we obtain a characterization of: i) regular, ii) deterministic context-free, and iii) type O languages, which is quite «natural» in terms of these algorithms. Furthermore, we show that, given a right linear or a strongLL(k) grammar, it is possible to produce automatically a pointer Markov algorithm parsing the language generated by the grammar. These constructions are particularly interesting because pointer Markov algorithms can be compiled conveniently into machine code programs.     

基于量子逻辑的图灵机及其通用性

基于量子逻辑的自动机理论是量子计算模型的一个重要研究方向.该文研究了基于量子逻辑的图灵机(简称量子图灵机)及其一些变形,给出了包括非确定型量子图灵机l-VTM,确定型量子图灵机l-VDTM以及相应类型的多带量子图灵机,并引入量子图灵机基于深度优先与宽度优先识别语言的两种不同定义方式,证明了这两种定义方式在量子逻辑意义下是不等价的.进一步证明了l-VTM、l-VDTM与相应类型的多带量子图灵机之间的等价性.其次,给出了量子递归可枚举语言及量子递归语言的定义,并给出了二者的层次刻画,证明了l-VTM与l-VDTM不等价,但两者作为量子递归语言的识别器是等价的.最后,文中讨论了基于量子逻辑的通用图灵机的存在性问题,给出了一套合理编码系统,证明了基于量子逻辑的通用图灵机在其所取值的正交模格无限时不存在,而在其所取值的正交模格有限时是存在的.     

Causal Message Sequence Charts

Scenario languages based on Message Sequence Charts (MSCs) have been widely studied in the last decade. The high expressive power of MSCs renders many basic problems concerning these languages undecidable. However, several of these problems are decidable for languages that possess a behavioral property called “existentially bounded”. Unfortunately, collections of scenarios outside this class are frequently exhibited by systems such as sliding window protocols. We propose here an extension of MSCs called causal Message Sequence Charts and a natural mechanism for defining languages of causal MSCs called causal HMSCs (CaHMSCs). These languages preserve decidable properties without requiring existential bounds. Further, they can model collections of scenarios generated by sliding window protocols. We establish here the basic theory of CaHMSCs as well as the expressive power and complexity of decision procedures for various subclasses of CaHMSCs. We also illustrate the modeling power of our formalism with the help of a realistic example based on the TCP sliding window feature.     

On LR(k) grammars and languages

Many different definitions for LR(k) grammars exist in the literature. One of these definitions is chosen and many important implications are drawn from it. In particular, the LR(k) characterization theorem provides valuable information about chains of derivations. The LR(0) languages are then characterized by acceptance by deterministic pushdown automata with a special termination condition, by a condition on the strings in the language, and set theoretically. Important closure properties of the LR(0) languages and a related class of languages are then examined. These are used to examine some decidability questions relating to the class of LR languages. One of these questions is shown to be equivalent to the equality problem for deterministic pushdown automata.A survey of other LR(k) definitions is given and the exact differences are characterized. On the basis of this analysis, justification for the choice of definition used here is provided.