There are examples of algorithms which allow the e cient computation of the concepts of a given formal context. However, when one wants to apply those algorithms to an arbitrary closure operator, which might not be given by a formal context, those algorithms cannot be applied directly. Therefore we want to discuss the problem of nding an appropriate formal context for a given closure operator, ...

Three-way concept analysis is an important tool for information processing, and rule acquisition one of the research hotspots three-way analysis. However, compared with lattices, semi-concept lattices have operators weaker constraints, which can generate more concepts. In this article, problem discussed in general. The authors construct finer relation propose a method lattices. also discuss set...

Extended Abstract Rewriting systems based on simple forms of productions play an important role in formal language theory. Therefore, it is no surprise that context-free grammars and their modifications are one of the most studied models. However, many of the systems describing practically interesting applications, such as the parsers of natural and programming languages, require additional mec...

It is well established that a formal language generated from a unimodal map is regular if and only if the map’s kneading sequence is either periodic or eventually periodic. A previously proposed conjecture said that if a language generated from a unimodal map is context-free, then it must be regular, i.e. there exists no proper context-free language which can be generated from a unimodal map. T...

The Seeheim Model of humancomputer interaction partitions an interactive application into a user-interface, a dialogue controller and the application itself. One of the formal techniques of implementing the dialogue controller is based on context-free grammars and automata. In this work, we modify an off-the-shelf compiler generator (YACC) to generate the dialogue controller. The dialogue contr...

In the Standard Generalized Markup Language (SGML), document types are deened by context-free grammars in an extended Backus-Naur form. The right-hand side of a production is called a content model. Content models are extended regular expressions that have to be unambiguous in the sense that \an element : : : that occurs in the document instance must be able to satisfy only one primitive conten...

The ancestor width is a new measure for the structure of derivations of arbitrary grammars. For every production used in a derivation or equivalently for every leaf we consider the strings of ancestors. The ancestors deene a complexity measure with a local avour. Obviously , context-free grammars have ancestor width one. We show that languages with ancestor width two are context-free. However, ...

Context-free grammars cannot be identified in the limit from positive examples (Gold 1967), yet natural language grammars are more powerful than context-free grammars and humans learn them with remarkable ease from positive examples (Marcus 1993). Identifiability results for formal languages ignore a potentially powerful source of information available to learners of natural languages, namely, ...

We consider the complexity of the equivalence and containment problems for regular expressions and context-free grammars, concentrating on the relationship between complexity and various language properties. Finiteness and boundedness of languages are shown to play important roles in the complexity of these problems. An encoding into grammars of Tur ing machine computations exponential in the s...