Formal language

About: Formal language is a research topic. Over the lifetime, 5763 publications have been published within this topic receiving 154114 citations.

Subregular Complexity and Deep Learning.

Abstract: This paper argues that the judicial use of formal language theory and grammatical inference are invaluable tools in understanding how deep neural networks can and cannot represent and learn long-term dependencies in temporal sequences Learning experiments were conducted with two types of Recurrent Neural Networks (RNNs) on six formal languages drawn from the Strictly Local (SL) and Strictly Piecewise (SP) classes The networks were Simple RNNs (s-RNNs) and Long Short-Term Memory RNNs (LSTMs) of varying sizes The SL and SP classes are among the simplest in a mathematically well-understood hierarchy of subregular classes They encode local and long-term dependencies, respectively The grammatical inference algorithm Regular Positive and Negative Inference (RPNI) provided a baseline According to earlier research, the LSTM architecture should be capable of learning long-term dependencies and should outperform s-RNNs The results of these experiments challenge this narrative First, the LSTMs' performance was generally worse in the SP experiments than in the SL ones Second, the s-RNNs out-performed the LSTMs on the most complex SP experiment and performed comparably to them on the others

Features aka the semantics of a formal language of manufacturing

Abstract: Features are application and viewer-dependent interpretations of geometry. This article demonstrates how the notion of features arising out of geometric data may be formalised as the semantics of a language of shape, using machining operations as an extended example. The syntax and semantics of formal languages are discussed, with particular reference to their use in design. A simplified lathe is defined, and a parametric attributed set grammar is presented which specifies the range of shapes manufacturable on that lathe. A simple feature space is then defined, in which feature models representing those shapes may be constructed. The link between the shapes and the feature models is then formalised as the semantics of the grammar using description functions, and it is shown how the feature models develop as shape generation proceeds. Finally, some implications of this work for feature-based design and manufacturing are discussed.

On the reachability and reversibility problems in a class of Petri nets

Abstract: The paper faces the reachability and the reversibility problems in a class of Petri nets larger than other classes investigated for the same problems. The considered class of Petri net represents a formal language to design and analyze logic controllers. These nets may be decomposed in simple structures, called elementary control tasks, linked together through a limited number of connections, giving rise to arbitrarily complex nets. Such connections are the ones encountered in a typical logic control problem, as exchange of enabling signals (consensus/deny to control maneuvers) and the synchronous execution (shared resources modeling or shared operations). The purpose of the paper is to enlarge the set of theoretical tools previously developed for the incremental approach to the liveness analysis of a net, to be incorporated into a special CAD environment. In particular, the addressed topics are the choice of the initial marking and the analysis of reachability of nonlive markings. >