Stefano Crespi Reghizzi | Politecnico di Milano (original) (raw)

Papers by Stefano Crespi Reghizzi

Research paper thumbnail of Breadth-first phrase structure grammars and queue automata

Lecture Notes in Computer Science

Without Abstract

Research paper thumbnail of Integer compositions and syntactic trees of repeat-until programs

In this work we study some properties of integer compositions in connection with the recognition ... more In this work we study some properties of integer compositions in connection with the recognition of rational trace languages. In particular, we introduce some operations defined on integer compositions and present procedures for their computation that work in linear or in quadratic time. These procedures turn out to be useful in the analysis of syntactic trees of certain regular expressions, called repeat-until expressions, which intuitively represent programs of instructions nested in repeat-until loops. Our main aim is to show how, in some cases, such an analysis allows us to design algorithms for the recognition of (rational) trace languages defined by repeat-until expressions, which work in quadratic time independently of the concurrency relation.

Research paper thumbnail of BSP: A Parsing Tool for Ambiguous Regular Expressions

Lecture Notes in Computer Science, 2015

and took place at Umeå Folkets hus during August 18-21, 2015. The CIAA conference series is the m... more and took place at Umeå Folkets hus during August 18-21, 2015. The CIAA conference series is the major international venue for the dissemination of new results in the implementation, application, and theory of automata. The previous 19 conferences were held in various locations all around the globe:

Research paper thumbnail of Algebraic ADT specifications of an extended relational algebra and their conversion into a working prototype

Lecture Notes in Computer Science

1. Introduction The core of relational data-base theory is the algebra of relations. In this cont... more 1. Introduction The core of relational data-base theory is the algebra of relations. In this context a rela-tion is a subset of a Cartesian product of some elementary domains. Algebraic operators are the set operations, projection, selection and product; other operators - notably join- ...

Research paper thumbnail of Towards a Brain Compatible Theory of Syntax Based on Local Testability

Topics in Computer Mathematics, 2003

Chomsky's theory of syntax came after criticism of probabilistic associative models of word order... more Chomsky's theory of syntax came after criticism of probabilistic associative models of word order in sentences. Immediate constituent structures are plausible but their description by generative grammars has met with difficulties. The type 2 (context-free) grammars account for constituent structure, but already trespass the mathematical capacity required by language, because they generate unnatural mathematical sets: a consequence of being based on recursive function theory. Abstract associative models investigated by formal language theoreticians (Schutzenberger, McNaughton, Papert, Brzozowsky, Simon) are known as locally testable models. A combination of locally testable and constituent structure models is proposed under the name of Associative Language Description, arguing that it equals type 2 grammars in explanatory adequacy, yet is compatible with brain models. Two versions of ALD are exemplified and discussed: one based on modulation, the other on pattern rules. A sketch of brain organization in terms of cell assemblies and synfire chains concludes. Key words and phrases. context-free grammar, word association, cell assemblies, synfire chains, non-counting property, grammar inference. This work was presented at the Workshop on Interdisciplinary approaches to a new understanding of cognition and consciousness, Villa Vigoni, Menaggio 1997. We acknowledge the support of Forschung für anwendungsorientierte Wissenverarbeitung, Ulm and of CNR-CESTIA.

Research paper thumbnail of Integrating object-oriented data modelling with a rule-based programming paradigm

ACM SIGMOD Record, 1990

LOGRES is a new project for the development of extended database systems which is based on the in... more LOGRES is a new project for the development of extended database systems which is based on the integration of the object-oriented data modelling paradigm and of the rule-based approach for the specification of queries and updates. The data model supports generalization hierarchies and object sharing, the rule-based language extends Datalog to support generalized type constructors (sets, multisets, and sequences), rule-based integrity constraints are automatically produced by analyzing schema definitions. Modularization is a fundamental feature, as modules encapsulate queries and updates, when modules are applied to a LOGRES database, their side effects can be controlled. The LOGRES project is a follow-up of the ALGRES project, and takes advantage of the ALGRES programming environment for the development of a fast prototype.

Research paper thumbnail of Regional Languages and Tiling: A Unifying Approach to Picture Grammars

Lecture Notes in Computer Science

Several classical models of picture grammars based on array rewriting rules can be unified and ex... more Several classical models of picture grammars based on array rewriting rules can be unified and extended by a tiling based approach. The right part of a rewriting rule is formalized by a finite set of permitted tiles. We focus on a simple type of tiling, named regional, and define the corresponding regional tile grammars. They include both Siromoney's (or Matz's) Kolam grammars, and their generalization by Průša. Regionally defined pictures can be recognized with polynomial time complexity by an algorithm extending the CKY one for strings. Regional tile grammars and languages are strictly included into the tile grammars and languages, and are incomparable with Giammarresi-Restivo tiling systems (or Wang's tilings).

Research paper thumbnail of Fair First Languages and Parallel Programme Schemes

Research paper thumbnail of An empirical investigation into a large-scale Java open source code repository

Proceedings of the 2010 ACM-IEEE International Symposium on Empirical Software Engineering and Measurement, 2010

Getting insight into different aspects of source code artifacts is increasingly important-yet the... more Getting insight into different aspects of source code artifacts is increasingly important-yet there is little empirical research using large bodies of source code, and subsequently there are not much statistically significant evidence of common patterns and facts of how programmers write source code. We pose 32 research questions, explain rationale behind them, and obtain facts from 2,080 randomly chosen Java applications from Sourceforge. Among these facts we find that most methods have one or zero arguments or they do not return any values, few methods are overridden, most inheritance hierarchies have the depth of one, close to 50% of classes are not explicitly inherited from any classes, and the number of methods is strongly correlated with the number of fields in a class.

Research paper thumbnail of Tile Rewriting Grammars

Lecture Notes in Computer Science, 2003

Past proposals for applying to pictures or 2D languages the generative grammar approach do not ma... more Past proposals for applying to pictures or 2D languages the generative grammar approach do not match in our opinion the elegance and descriptive adequacy that made Context Free grammars so successful for 1D languages. In a renewed attempt, a model named Tile Rewriting Grammar is introduced combining the rewriting rules with the Tiling System of Giammaresi and Restivo which define the family of Recognizable 2D languages. The new grammars have isometric rewriting rules which for string languages are equivalent to CF rules. TRG have the capacity to generate a sort of 2D analogues of Dyck languages. Closure properties of TRG are proved for some basic operations. TRG strictly include TS as well as the context-free picture grammars of Matz.

Research paper thumbnail of Real-time scheduling by queue automata

Lecture Notes in Computer Science, 1992

ABSTRACT Real-time schedulers are modelled by finite-state transition systems using FIFO queues a... more ABSTRACT Real-time schedulers are modelled by finite-state transition systems using FIFO queues as auxiliary memory. The intuitive notion of hard real time is related to the definition of quasi-real-time behaviour of an automaton. Then, starting with simple schedulers for independent tasks, a modular approach to the design of schedulers (FIFO, static priority based, preemptive, dynamic priorities) is presented. This is based on recent results on recognition power and closure properties of quasi-real-time queue automata w.r.t. intersection, shuffle and reverse homomorphism. The treatment of readers-writers schedulers is compared with recent proposals based on intersections of context-free languages. Possible developments are in the conclusion.

Research paper thumbnail of Deterministic dequeue automata and LL(1) parsing of breadth-depth grammars

Lecture Notes in Computer Science, 1991

Breadth-depth grammars [3] extend the context-free ones by allowing breadthfirst derivations. Bre... more Breadth-depth grammars [3] extend the context-free ones by allowing breadthfirst derivations. Breadth-depth languages include the context-free ones and are recognized by monostatic (one-state) automata having a double-ended queue (dequeue) as their memory. Examples of breadth-depth grammars for compilation and scheduling problems are included to argue for their applicability. We define deterministic monostatic dequeue automata and investigate their languages. Main results are their incomparability with context-free deterministic languages and linear-time recognizability. We introduce the LL(1) grammars, as an extension of the classical top-down deterministically parsable context-free grammars, and we present a recursive descent parsing algorithm using a FIFO queue.

Research paper thumbnail of Deterministic parsing for augmented context-free grammars

Lecture Notes in Computer Science, 1995

Page 1. Deterministic Parsing for Augmented Context-free Grammars* Luca Breveglieri tAlessandra C... more Page 1. Deterministic Parsing for Augmented Context-free Grammars* Luca Breveglieri tAlessandra Cherubini$ Stefano Crespi Reghizzi t ... A CF gram-mars can be classified with respect to their disposition, a concept related to the data structure needed to parse their strings. ...

Research paper thumbnail of Modeling operating systems schedulers with multi-stack-queue grammars

Lecture Notes in Computer Science, 1999

... di Elettronica e Informazione, e-mail: Stefano.Crespi-Reghizzi@Elet.PoliMi.IT, Luca.Breveglie... more ... di Elettronica e Informazione, e-mail: Stefano.Crespi-Reghizzi@Elet.PoliMi.IT, Luca.Breveglieri@ Elet.PoliMi.IT 2 Politecnico di Milano, Dipartimento di Matematica, e-mail: Alessandra.Cherubini@ Mate ... The classical model of attribute gram-mars conveniently fits ABNF grammars ...

Research paper thumbnail of PAPAGENO: A parallel parser generator for operator precedence grammars

Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics), 2013

In almost all language processing applications, languages are parsed employing classical algorith... more In almost all language processing applications, languages are parsed employing classical algorithms (such as the LR(1) parsers generated by Bison), which are sequential due to their left-to-right state-dependent nature. Although early theoretical studies on parallel parsing algorithms delineated potential speedups on abstract parallel machines using a data-parallel approach, practical developments have not materialized, except in recent experiments on ad hoc parsers for large XML files. We describe a general-purpose practical generator (PA-PAGENO) able to produce efficient deterministic parallel parsers, which exhibit significant speedups when parsing large texts on modern multi-core machines, while not penalizing sequential operation. The generated parser relies on the properties of Floyd's operator precedence grammars, to provide a naturally parallel implementation of the parsing process. Parsing of each text portion proceeds in parallel and independently, without communication and synchronization, until all partial parse stacks are recombined into the final result. Since Floyd's grammars can express most syntaxes with little adaptation, we have performed extensive experiments, on both synthetically generated texts and real JSON documents. The effective parallel code portion in the generated parsers exceeds 80% for most of the tested scenarios.

Research paper thumbnail of Tile rewriting grammars and picture languages

Theoretical Computer Science, 2005

Tile Rewriting Grammars (TRG) are a new model for defining picture languages. A rewriting rule ch... more Tile Rewriting Grammars (TRG) are a new model for defining picture languages. A rewriting rule changes a homogeneous rectangular subpicture into a isometric one tiled with specified tiles. Derivation and language generation with TRG rules are similar to contextfree grammars. A normal form and some closure properties are presented. We prove this model has greater generative capacity than the Tiling Systems of Giammarresi and Restivo and the grammars of Matz, another generalization of context free string grammars to 2D. Examples are shown for pictures made by nested frames and spirals.

Research paper thumbnail of QRT FIFO automata, breadth-first grammars and their relations

Theoretical Computer Science, 1991

A., C. Citrini, S.C. Reghizzi, and D. Mandrioli, QRT FIFO automata, breadth-first grammars and th... more A., C. Citrini, S.C. Reghizzi, and D. Mandrioli, QRT FIFO automata, breadth-first grammars and their relations, Theoretical Computer Science 85 (1991) 171-203.

Research paper thumbnail of On Deterministic Multi-Pass Analysis

SIAM Journal on Computing, 1986

Chains (or cascade composition) of push-down transducers are introduced as a model of multi-pass ... more Chains (or cascade composition) of push-down transducers are introduced as a model of multi-pass compilers. We focus on deterministic chains, since nondeterministic transducer chains of length two define the recursively enumerable sets. Deterministic chains recognize in linear time a superset of context-free deterministic languages. This family is mathcalCH\mathcal{CH}mathcalCH closed under Boolean operations, disjoint shuffle,and reverse deterministic pushdown translation, but not under homomorphism. Equivalent definitions of the family in terms of composition of syntax-directed translation schemes and control languages are considered. The family is a strict hierarchy ordered by the length of the chain. The complexity of mathcalCH\mathcal{CH}mathcalCH is obviously linear, but not all linear-time parsable languages are in mathcalCH\mathcal{CH}mathcalCH. On the other hand it strictly includes the Boolean closure of deterministic languages. Finally mathcalCH\mathcal{CH}mathcalCH is not comparable with another classical Boolean algebra of formal languages, namely real-ti...

Research paper thumbnail of A SAT-based parser and completer for pictures specified by tiling

Pattern Recognition, 2008

Pictures or patterns have been formally specified by different methods such as grammars. An alter... more Pictures or patterns have been formally specified by different methods such as grammars. An alternative approach is based on Tiling Systems (TS) (Wang tiles are an analogous and equivalent formalism), whereby the picture is obtained by first covering it with a specified set of two by two tiles, then by performing a pixel by pixel mapping. TS are a powerful technique: the corresponding pictures can be recognized by non-deterministic cellular automata, which are more powerful then the four ways automata. The difficulty to write such specifications for non elementary pictures, and the NP-complete computational complexity of TS picture recognition have so far blocked any attempt to application. We have implemented a recognizer and generator for TS pictures in a very attractive, unconventional way, by transforming the tiling problem into a SAT (Boolean Satisfiability) one, then using an efficient off-the-shelf SAT-solver. The prototype is fast enough to experiment on reasonably sized samples, and has the bonus of being able to complete or extrapolate a partial or noisy picture. The tool is invaluable to assist in writing picture specification. A series of examples shows how to specify patterns using TS.

Research paper thumbnail of Multi-Push-Down Languages and Grammars

International Journal of Foundations of Computer Science, 1996

A new class of languages, called multi-push-down (mpd), that generalize the classical context-fre... more A new class of languages, called multi-push-down (mpd), that generalize the classical context-free (cf, or Chomsky type 2) ones is introduced. These languages preserve some important properties of cf languages: a generalization of the Chomsky-Schützenberger homomorphic characterization theorem, the Parikh theorem and a “pumping lemma” are proved. Multi-push-down languages are an AFL. Their recognizers are automata equipped with a multi-push-down tape. Multi-push-down languages form a hierarchy based on the number of push-down tapes.

Research paper thumbnail of Breadth-first phrase structure grammars and queue automata

Lecture Notes in Computer Science

Without Abstract

Research paper thumbnail of Integer compositions and syntactic trees of repeat-until programs

In this work we study some properties of integer compositions in connection with the recognition ... more In this work we study some properties of integer compositions in connection with the recognition of rational trace languages. In particular, we introduce some operations defined on integer compositions and present procedures for their computation that work in linear or in quadratic time. These procedures turn out to be useful in the analysis of syntactic trees of certain regular expressions, called repeat-until expressions, which intuitively represent programs of instructions nested in repeat-until loops. Our main aim is to show how, in some cases, such an analysis allows us to design algorithms for the recognition of (rational) trace languages defined by repeat-until expressions, which work in quadratic time independently of the concurrency relation.

Research paper thumbnail of BSP: A Parsing Tool for Ambiguous Regular Expressions

Lecture Notes in Computer Science, 2015

and took place at Umeå Folkets hus during August 18-21, 2015. The CIAA conference series is the m... more and took place at Umeå Folkets hus during August 18-21, 2015. The CIAA conference series is the major international venue for the dissemination of new results in the implementation, application, and theory of automata. The previous 19 conferences were held in various locations all around the globe:

Research paper thumbnail of Algebraic ADT specifications of an extended relational algebra and their conversion into a working prototype

Lecture Notes in Computer Science

1. Introduction The core of relational data-base theory is the algebra of relations. In this cont... more 1. Introduction The core of relational data-base theory is the algebra of relations. In this context a rela-tion is a subset of a Cartesian product of some elementary domains. Algebraic operators are the set operations, projection, selection and product; other operators - notably join- ...

Research paper thumbnail of Towards a Brain Compatible Theory of Syntax Based on Local Testability

Topics in Computer Mathematics, 2003

Chomsky's theory of syntax came after criticism of probabilistic associative models of word order... more Chomsky's theory of syntax came after criticism of probabilistic associative models of word order in sentences. Immediate constituent structures are plausible but their description by generative grammars has met with difficulties. The type 2 (context-free) grammars account for constituent structure, but already trespass the mathematical capacity required by language, because they generate unnatural mathematical sets: a consequence of being based on recursive function theory. Abstract associative models investigated by formal language theoreticians (Schutzenberger, McNaughton, Papert, Brzozowsky, Simon) are known as locally testable models. A combination of locally testable and constituent structure models is proposed under the name of Associative Language Description, arguing that it equals type 2 grammars in explanatory adequacy, yet is compatible with brain models. Two versions of ALD are exemplified and discussed: one based on modulation, the other on pattern rules. A sketch of brain organization in terms of cell assemblies and synfire chains concludes. Key words and phrases. context-free grammar, word association, cell assemblies, synfire chains, non-counting property, grammar inference. This work was presented at the Workshop on Interdisciplinary approaches to a new understanding of cognition and consciousness, Villa Vigoni, Menaggio 1997. We acknowledge the support of Forschung für anwendungsorientierte Wissenverarbeitung, Ulm and of CNR-CESTIA.

Research paper thumbnail of Integrating object-oriented data modelling with a rule-based programming paradigm

ACM SIGMOD Record, 1990

LOGRES is a new project for the development of extended database systems which is based on the in... more LOGRES is a new project for the development of extended database systems which is based on the integration of the object-oriented data modelling paradigm and of the rule-based approach for the specification of queries and updates. The data model supports generalization hierarchies and object sharing, the rule-based language extends Datalog to support generalized type constructors (sets, multisets, and sequences), rule-based integrity constraints are automatically produced by analyzing schema definitions. Modularization is a fundamental feature, as modules encapsulate queries and updates, when modules are applied to a LOGRES database, their side effects can be controlled. The LOGRES project is a follow-up of the ALGRES project, and takes advantage of the ALGRES programming environment for the development of a fast prototype.

Research paper thumbnail of Regional Languages and Tiling: A Unifying Approach to Picture Grammars

Lecture Notes in Computer Science

Several classical models of picture grammars based on array rewriting rules can be unified and ex... more Several classical models of picture grammars based on array rewriting rules can be unified and extended by a tiling based approach. The right part of a rewriting rule is formalized by a finite set of permitted tiles. We focus on a simple type of tiling, named regional, and define the corresponding regional tile grammars. They include both Siromoney's (or Matz's) Kolam grammars, and their generalization by Průša. Regionally defined pictures can be recognized with polynomial time complexity by an algorithm extending the CKY one for strings. Regional tile grammars and languages are strictly included into the tile grammars and languages, and are incomparable with Giammarresi-Restivo tiling systems (or Wang's tilings).

Research paper thumbnail of Fair First Languages and Parallel Programme Schemes

Research paper thumbnail of An empirical investigation into a large-scale Java open source code repository

Proceedings of the 2010 ACM-IEEE International Symposium on Empirical Software Engineering and Measurement, 2010

Getting insight into different aspects of source code artifacts is increasingly important-yet the... more Getting insight into different aspects of source code artifacts is increasingly important-yet there is little empirical research using large bodies of source code, and subsequently there are not much statistically significant evidence of common patterns and facts of how programmers write source code. We pose 32 research questions, explain rationale behind them, and obtain facts from 2,080 randomly chosen Java applications from Sourceforge. Among these facts we find that most methods have one or zero arguments or they do not return any values, few methods are overridden, most inheritance hierarchies have the depth of one, close to 50% of classes are not explicitly inherited from any classes, and the number of methods is strongly correlated with the number of fields in a class.

Research paper thumbnail of Tile Rewriting Grammars

Lecture Notes in Computer Science, 2003

Past proposals for applying to pictures or 2D languages the generative grammar approach do not ma... more Past proposals for applying to pictures or 2D languages the generative grammar approach do not match in our opinion the elegance and descriptive adequacy that made Context Free grammars so successful for 1D languages. In a renewed attempt, a model named Tile Rewriting Grammar is introduced combining the rewriting rules with the Tiling System of Giammaresi and Restivo which define the family of Recognizable 2D languages. The new grammars have isometric rewriting rules which for string languages are equivalent to CF rules. TRG have the capacity to generate a sort of 2D analogues of Dyck languages. Closure properties of TRG are proved for some basic operations. TRG strictly include TS as well as the context-free picture grammars of Matz.

Research paper thumbnail of Real-time scheduling by queue automata

Lecture Notes in Computer Science, 1992

ABSTRACT Real-time schedulers are modelled by finite-state transition systems using FIFO queues a... more ABSTRACT Real-time schedulers are modelled by finite-state transition systems using FIFO queues as auxiliary memory. The intuitive notion of hard real time is related to the definition of quasi-real-time behaviour of an automaton. Then, starting with simple schedulers for independent tasks, a modular approach to the design of schedulers (FIFO, static priority based, preemptive, dynamic priorities) is presented. This is based on recent results on recognition power and closure properties of quasi-real-time queue automata w.r.t. intersection, shuffle and reverse homomorphism. The treatment of readers-writers schedulers is compared with recent proposals based on intersections of context-free languages. Possible developments are in the conclusion.

Research paper thumbnail of Deterministic dequeue automata and LL(1) parsing of breadth-depth grammars

Lecture Notes in Computer Science, 1991

Breadth-depth grammars [3] extend the context-free ones by allowing breadthfirst derivations. Bre... more Breadth-depth grammars [3] extend the context-free ones by allowing breadthfirst derivations. Breadth-depth languages include the context-free ones and are recognized by monostatic (one-state) automata having a double-ended queue (dequeue) as their memory. Examples of breadth-depth grammars for compilation and scheduling problems are included to argue for their applicability. We define deterministic monostatic dequeue automata and investigate their languages. Main results are their incomparability with context-free deterministic languages and linear-time recognizability. We introduce the LL(1) grammars, as an extension of the classical top-down deterministically parsable context-free grammars, and we present a recursive descent parsing algorithm using a FIFO queue.

Research paper thumbnail of Deterministic parsing for augmented context-free grammars

Lecture Notes in Computer Science, 1995

Page 1. Deterministic Parsing for Augmented Context-free Grammars* Luca Breveglieri tAlessandra C... more Page 1. Deterministic Parsing for Augmented Context-free Grammars* Luca Breveglieri tAlessandra Cherubini$ Stefano Crespi Reghizzi t ... A CF gram-mars can be classified with respect to their disposition, a concept related to the data structure needed to parse their strings. ...

Research paper thumbnail of Modeling operating systems schedulers with multi-stack-queue grammars

Lecture Notes in Computer Science, 1999

... di Elettronica e Informazione, e-mail: Stefano.Crespi-Reghizzi@Elet.PoliMi.IT, Luca.Breveglie... more ... di Elettronica e Informazione, e-mail: Stefano.Crespi-Reghizzi@Elet.PoliMi.IT, Luca.Breveglieri@ Elet.PoliMi.IT 2 Politecnico di Milano, Dipartimento di Matematica, e-mail: Alessandra.Cherubini@ Mate ... The classical model of attribute gram-mars conveniently fits ABNF grammars ...

Research paper thumbnail of PAPAGENO: A parallel parser generator for operator precedence grammars

Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics), 2013

In almost all language processing applications, languages are parsed employing classical algorith... more In almost all language processing applications, languages are parsed employing classical algorithms (such as the LR(1) parsers generated by Bison), which are sequential due to their left-to-right state-dependent nature. Although early theoretical studies on parallel parsing algorithms delineated potential speedups on abstract parallel machines using a data-parallel approach, practical developments have not materialized, except in recent experiments on ad hoc parsers for large XML files. We describe a general-purpose practical generator (PA-PAGENO) able to produce efficient deterministic parallel parsers, which exhibit significant speedups when parsing large texts on modern multi-core machines, while not penalizing sequential operation. The generated parser relies on the properties of Floyd's operator precedence grammars, to provide a naturally parallel implementation of the parsing process. Parsing of each text portion proceeds in parallel and independently, without communication and synchronization, until all partial parse stacks are recombined into the final result. Since Floyd's grammars can express most syntaxes with little adaptation, we have performed extensive experiments, on both synthetically generated texts and real JSON documents. The effective parallel code portion in the generated parsers exceeds 80% for most of the tested scenarios.

Research paper thumbnail of Tile rewriting grammars and picture languages

Theoretical Computer Science, 2005

Tile Rewriting Grammars (TRG) are a new model for defining picture languages. A rewriting rule ch... more Tile Rewriting Grammars (TRG) are a new model for defining picture languages. A rewriting rule changes a homogeneous rectangular subpicture into a isometric one tiled with specified tiles. Derivation and language generation with TRG rules are similar to contextfree grammars. A normal form and some closure properties are presented. We prove this model has greater generative capacity than the Tiling Systems of Giammarresi and Restivo and the grammars of Matz, another generalization of context free string grammars to 2D. Examples are shown for pictures made by nested frames and spirals.

Research paper thumbnail of QRT FIFO automata, breadth-first grammars and their relations

Theoretical Computer Science, 1991

A., C. Citrini, S.C. Reghizzi, and D. Mandrioli, QRT FIFO automata, breadth-first grammars and th... more A., C. Citrini, S.C. Reghizzi, and D. Mandrioli, QRT FIFO automata, breadth-first grammars and their relations, Theoretical Computer Science 85 (1991) 171-203.

Research paper thumbnail of On Deterministic Multi-Pass Analysis

SIAM Journal on Computing, 1986

Chains (or cascade composition) of push-down transducers are introduced as a model of multi-pass ... more Chains (or cascade composition) of push-down transducers are introduced as a model of multi-pass compilers. We focus on deterministic chains, since nondeterministic transducer chains of length two define the recursively enumerable sets. Deterministic chains recognize in linear time a superset of context-free deterministic languages. This family is mathcalCH\mathcal{CH}mathcalCH closed under Boolean operations, disjoint shuffle,and reverse deterministic pushdown translation, but not under homomorphism. Equivalent definitions of the family in terms of composition of syntax-directed translation schemes and control languages are considered. The family is a strict hierarchy ordered by the length of the chain. The complexity of mathcalCH\mathcal{CH}mathcalCH is obviously linear, but not all linear-time parsable languages are in mathcalCH\mathcal{CH}mathcalCH. On the other hand it strictly includes the Boolean closure of deterministic languages. Finally mathcalCH\mathcal{CH}mathcalCH is not comparable with another classical Boolean algebra of formal languages, namely real-ti...

Research paper thumbnail of A SAT-based parser and completer for pictures specified by tiling

Pattern Recognition, 2008

Pictures or patterns have been formally specified by different methods such as grammars. An alter... more Pictures or patterns have been formally specified by different methods such as grammars. An alternative approach is based on Tiling Systems (TS) (Wang tiles are an analogous and equivalent formalism), whereby the picture is obtained by first covering it with a specified set of two by two tiles, then by performing a pixel by pixel mapping. TS are a powerful technique: the corresponding pictures can be recognized by non-deterministic cellular automata, which are more powerful then the four ways automata. The difficulty to write such specifications for non elementary pictures, and the NP-complete computational complexity of TS picture recognition have so far blocked any attempt to application. We have implemented a recognizer and generator for TS pictures in a very attractive, unconventional way, by transforming the tiling problem into a SAT (Boolean Satisfiability) one, then using an efficient off-the-shelf SAT-solver. The prototype is fast enough to experiment on reasonably sized samples, and has the bonus of being able to complete or extrapolate a partial or noisy picture. The tool is invaluable to assist in writing picture specification. A series of examples shows how to specify patterns using TS.

Research paper thumbnail of Multi-Push-Down Languages and Grammars

International Journal of Foundations of Computer Science, 1996

A new class of languages, called multi-push-down (mpd), that generalize the classical context-fre... more A new class of languages, called multi-push-down (mpd), that generalize the classical context-free (cf, or Chomsky type 2) ones is introduced. These languages preserve some important properties of cf languages: a generalization of the Chomsky-Schützenberger homomorphic characterization theorem, the Parikh theorem and a “pumping lemma” are proved. Multi-push-down languages are an AFL. Their recognizers are automata equipped with a multi-push-down tape. Multi-push-down languages form a hierarchy based on the number of push-down tapes.