Characterizing sets of data structures by the connectivity relation

A formalism based on the directed graph connectivity relation is presented, in which a first-order predicate calculus notation is used with the purpose of defining sets of data structures and characterizing the structural operations on them. The formalism is designed so as to facilitate the proof that the intended operations on instances of a given set of data structures are correct, in the sense that they do not violate the structural form of the data.     

Case studies in asynchronous data parallelism

Is the owner-computes style of parallelism, captured in a variety of data parallel languages, attractive as a paradigm for designing explicit control parallel codes? This question gives rise to a number of others. Will such use be unwieldy? Will the resulting code run well? What can such an approach offer beyond merely replicating, in a more labor intensive way, the services and coverage of data parallel languages? We investigate these questions via a simple example and “real world” case studies developed using C-Linda, a language for explicit parallel programming formed by the merger of C with the Linda coordination language. The results demonstrate owner-computes is an effective design strategy in Linda.     

KALA: Kernel aspect language for advanced transactions

Transaction management is a known crosscutting concern. Previous research has been conducted to express this concern as an aspect. However, such work has used general-purpose aspect languages which lack a formal foundation, and most importantly are unable to express advanced models of transaction management. In this paper, we propose a domain-specific aspect language for advanced transaction management, called KALA, that overcomes these limitations. First, KALA is based on a recognized formalism for the domain of advanced transaction management, called ACTA. Second, as a consequence of being based on the ACTA formalism, KALA covers a wide variety of models for transaction management. Finally, being a domain-specific aspect language, KALA allows programmers to express their needs at a higher level of abstraction than what is achieved with general-purpose aspect languages. This paper reports on the design of KALA and its implementation over Java, based on the Reflex AOP kernel for domain-specific aspect languages.     

Algebraic properties on the cuts of lattice-valued regular languages

In this paper, the algebraic operations on the cuts of lattice-valued regular languages are studied. Some sufficient conditions are given to guarantee the family of the cuts of lattice-valued regular languages to be closed under such algebraic operations as union, intersection, complement, quotient, homomorphism, inverse homomorphism, concatennation, reversal, etc. This work is supported by National Science Foundation of China (Grant No.10571112), “TRAPOYT” of China and National 973 Foundation Research Program (Grant No. 2002CB312200).     

An intermediate language to define dynamic semantics

An instruction set is given for an abstract machine which uses a pushdown stack as its principal memory. The proposed instructions serve the similar purposes of (1) defining the dynamic semantics of programming languages by describing the operations of programs on the abstract machine and (2) describing an intermediate language to be used in compiling programming languages into machine language. It is shown how the intermediate language can be used in the translation of the programming languages ADA, FORTRAN and PASCAL into IBM 360 assembly language and advantages over other intermediate languages such as three-address code and P-code.     

Synchronous Dataflow Pattern Matching

We introduce variant types and a pattern matching operation to synchronous dataflow languages. These languages are used in the design of reactive systems. As these systems grow increasingly complex, the need for abstraction mechanisms, in particular, data and control structures, is critical. Variant types provide a mechanism to precisely model structured data. The pattern matching operation, defined as a clock operator, provides an efficient control structure.     

Defining the abstract syntax of visual languages with advanced graph grammars—A case study based on behavior trees

Diagrammatic visual languages can increase the ability of engineers to model and understand complex systems. However, to effectively use visual models, the syntax and semantics of these languages should be defined precisely. Since most diagrammatic visual models that are currently used to specify systems can be described as (directed) typed graphs, graph grammars have been identified as a suitable formalism to describe the abstract syntax of visual modeling languages. In this article, we investigate how advanced graph-transformation techniques, such as conditional, structure-generic and type-generic graph-transformation rules, can help to improve and simplify the specification of the abstract syntax of a visual modeling language. To demonstrate the practicability of an approach that unifies these advanced graph-transformation techniques, we define the abstract syntax of behavior trees (BTs), a graphical specification language for functional requirements. Additionally, we provide a translational semantics of BTs by formalizing a translation scheme to the input language of the SAL model checking tool for each of the graph-transformation rules.     

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.     

Modeling events as entities in object-oriented conceptual modeling languages

Most current conceptual modeling languages and methods do not model events as entities. We argue that, at least in object-oriented (O-O) languages, modeling events as entities provides substantial benefits. We show that a method for behavioral modeling that deals with event and entity types in a uniform way may yield better behavioral schemas. The proposed method makes extensive use of language constructs such as constraints, derived types, derivation rules, type specializations and operations, which are present in all complete O-O conceptual modeling languages. The method can be adapted to most O-O languages. In this paper we explain its adaptation to the UML.     

Highly Constrained Unification Grammars

Unification grammars are widely accepted as an expressive means for describing the structure of natural languages. In general, the recognition problem is undecidable for unification grammars. Even with restricted variants of the formalism, off-line parsable grammars, the problem is computationally hard. We present two natural constraints on unification grammars which limit their expressivity and allow for efficient processing. We first show that non-reentrant unification grammars generate exactly the class of context-free languages. We then relax the constraint and show that one-reentrant unification grammars generate exactly the class of mildly context-sensitive languages. We thus relate the commonly used and linguistically motivated formalism of unification grammars to more restricted, computationally tractable classes of languages.     

String and graph grammar characterizations of bounded regular languages

Two grammatical characterizations of the bounded regular languages are presented: one in terms of graph grammars, the other using string grammars. First it is shown that a class of state graphs recognizing the bounded regular languages can be generated by a particular second-order contextfree graph grammar. Next we call uniquely recursive a right-linear (string) grammar having at most one right-recursive production for each of its nonterminals. It is then established that the class of languages generated by uniquely recursive, sequential right-linear grammars is exactly the bounded regular languages. Some comments on the relationship between string and graph grammars are made.     

Hierarchical development of programming languages

The experience in designing large software systems shows that even the definitions of a programming language can be seen as the application of specific implementation and formalization techniques rather than as the result of a «designing art». In this context, a formalism is proposed here as a tool for defining conventional high level programming languages. The formalism is an algebraic model supporting the definition of representational entities such as types. A Type is a set of data and operations on them. An isomorphism between language components and types realizes an isomorphism between the language and its specification on the model. Then, the definition of a language can be performed by stepwise definitions of the types representing the language components. So the model is also a language development tool. Stepwise definition methodologies are also investigated and two are the proposed ones: the horizontal, methodology and the vertical methodology. In particular, the vertical methodology defines languages by the development of a hierarchy of abstraction levels, each corresponding to one class of languages: The last class only contains the language being defined.     

Deletion along trajectories

We describe a new way to model deletion operations on formal languages, called deletion along trajectories. We examine its closure properties, which differ from those of shuffle on trajectories, previously introduced by Mateescu et al. In particular, we define classes of non-regular sets of trajectories such that the associated deletion operation preserves regularity. Our results give uniform proofs of closure properties of the regular languages for several deletion operations.

We also show that deletion along trajectories serves as an inverse to shuffle on trajectories. This leads to results on the decidability of certain language equations, including those of the form LTX=R, where L,R are regular languages and X is unknown.     

Simple-english for data base communication

Three classes of the so-called natural languages for communication with data bases are defined:English-like, pseudo-English, andsimple-English. It is argued that English-like and pseudo-English languages are normally more difficult to learn and use than artificial programming languages with no overt claim to English likeness. Simple-English is presented as a family of languages in which many restrictions (which hamper learning) are removed through interaction with, and drawing inferences from, the data base and the underlying system. It is concluded, however, that English likeness and ease of learning may be contradictory notions.     

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.     

Parameter passing mechanisms and run time data structures

The relationship between parameter passing mechanisms and run time data structures in languages with statically-nested scopes is examined. It is shown that simpler data structures can be used in some cases, with increased efficiency in accessing non-local variables. In particular it is true for the call-by-value-result mechanism, where the usage of displays can be eliminated altogether; however there is some additional cost associated with procedure calls. Under certain conditions the same implementation applies to call-by-reference.