The use of water for agricultural production in water scarcity regions requires innovative and su... more The use of water for agricultural production in water scarcity regions requires innovative and sustainable research, and an appropriate transfer of technologies. This paper discusses some of these aspects, mainly relative to on-farm irrigation management including the use of treated wastewater and saline waters. First, the paper proposes some concepts relative to water scarcity, concerning aridity, drought, deserti®cation and water shortage, as well as policies to cope with these water stressed regimes. Conceptual approaches on irrigation performances, water use and water savings are reviewed in a wide perspective. This is followed by a discussion of supply management to cope with water scarcity, giving particular attention to the use of wastewater and low-quality waters, including the respective impacts on health and the environment as water scarcity is requiring that waters of inferior quality be increasingly used for irrigation. The paper then focuses on demand management, starting with aspects relating to the improvement of irrigation methods and the respective performances, mainly the distribution uniformity (DU) as a fundamental tool to reduce the demand for water at the farm level, and to control the negative environmental impacts of over-irrigation, including salt stressed areas. Discussions are supported by recent research results. The suitability of irrigation methods for using treated wastewaters and saline waters is analysed. Supplemental irrigation (SI) and de®cit irrigation strategies are also discussed, including limitations on the applicability of related practices. The paper also identi®es the need to adopt emerging technologies for water management as well as to develop appropriate methodologies for the analysis of social, economic, and environmental bene®ts of improved irrigation management. #
The use of traditional backtracking to explore a search space top-down starts with the initial st... more The use of traditional backtracking to explore a search space top-down starts with the initial state as the current state. Then, for each forward derivation step, one of the operators applicable to the current state is used to derive a new current state. This forward execution is repeated until either a solution state is reached and success is reported, or the set ofuriused operators applicable to the current state is empty. At this point, the search backtracks. The current state is dropped, its predecessor is reinstated as the current state, and forward ...
Wide-bandgap high-mobility ZnO thin-film transistors produced at room temperature. [Applied Physi... more Wide-bandgap high-mobility ZnO thin-film transistors produced at room temperature. [Applied Physics Letters 85, 2541 (2004)]. Elvira MC Fortunato, Pedro MC Barquinha, Ana CMBG Pimentel, Alexandra MF Gonçalves, António JS Marques, Rodrigo FP Martins, Luis MN Pereira. ...
Functional oxide materials currently represent a key challenge as well as a promising powerful to... more Functional oxide materials currently represent a key challenge as well as a promising powerful tool for both fundamental understanding and technological development of the next generation of transparent electronics, such as field-effect transistors. Here, we report a fully transparent ZnO thin-film transistor (ZnO-TFT) with a transmittance above 80 % in the visible part of the spectrum, including the glass substrate, fabricated by radiofrequency (rf) magnetron sputtering at room temperature, with a bottom gate configuration. The ZnO-TFT operates in the enhancement mode, exhibiting a high saturation mobility of about 20 cm 2 V ±1 s ±1 , a threshold voltage of 21 V, a gate-voltage swing of 1.24 V decade ±1 , and an on/off ratio of 2 10 5 . Besides this, the off resistance is on the order of 20 MX and the on resistance is on the order of 45 kX. The combination of transparency, high mobility, and room-temperature processing makes the ZnO-TFT a very promising lowcost optoelectronic device for the next generation of invisible and flexible electronics, such as switching for addressing active matrices based on organic light-emitting diodes (OLEDs).
The agent paradigm, commonly implemented by means of imperative languages mainly for reasons of e... more The agent paradigm, commonly implemented by means of imperative languages mainly for reasons of efficiency, has recently increased its influence in the research and development of computational logic based systems. Since efficiency is not always the crucial issue, but clear specification and correctness is, Logic Programming and Non-monotonic Reasoning have been brought back into the spotlight. To this accrues the recent significant improvements in the efficiency of Logic Programming implementations for Non-monotonic Reasoning. This paper presents an overall description of MIN ERVA, an agent architecture and system designed with the intention of providing a common agent framework based on the unique strengths of Logic Programming, to allow for the combination of several non-monotonic knowledge representation and reasoning mechanisms developed in recent years. In [10], the semantics of the multi-dimensional structure and combination of the evolving societal knowledge of agents in described and discussed in detail.
Abstract Well Founded Semantics is adequate to capture nonmonotonic reasoning if we interpret the... more Abstract Well Founded Semantics is adequate to capture nonmonotonic reasoning if we interpret the Well Founded model of a program P as a (possibly incomplete) view of the world. Thus the Well Founded model may be accepted to be a definite view of the world and the extended stable models as alternative enlarged consistent belief models an agent may have about the world. Our purpose is to exhibit a modular systematic method of representing nonmonotonic problems with the Well Founded semantics of logic programs. In this paper ...
Recently the field of theory update has seen some improvement, in what concerns model updating, b... more Recently the field of theory update has seen some improvement, in what concerns model updating, by allowing updates to be specified by so-called revision programs. The updating of theory models is governed by their update rules and also by inertia applied to those literals not directly affected by the update program. Though this is important, it remains necessary to tackle as well the updating of programs specifying theories. Some results have been obtained on the issue of updating a logic program which encodes a set of models, to obtain a new program whose models are the desired updates of the initial models. But here the program only plays the rÔle of a means to encode the models. A logic program encodes much more than a set of models: it encodes knowledge in the form of the relationships between the elements of those models. In this paper we advocate that the principle of inertia is advantageously applied to the rules of the initial program rather than to the individual literals in a model. Indeed, we show how this concept of program update generalizes model or interpretation updates. Furthermore, it allows us to conceive what it is to update one program by another, a crucial notion for opening up a whole new range of applications concerning the evolution of knowledge bases. We will consider the updating of normal programs as well as these extended with explicit negation, under the stable semantics.
This paper reports on the use of logic program updates to models actions that bring about changes... more This paper reports on the use of logic program updates to models actions that bring about changes in knowledge states describing the world and its rules. The LUPS language is employed to specify concurrent update rules to model actions that depend on, and change, rule rich world states, not described simply by propositional uents. This language and corresponding semantics, whose original stable semantics we generalize to the well-founded setting, is brie y recapitulated here.
1 Language An extended logic program (or x-program) P is a set of rules of the form: H &a... more 1 Language An extended logic program (or x-program) P is a set of rules of the form: H <— Bi,... ,Bn, not Ci,... ,not Cm where n,m > 0 and H,B.¡,Ci arc objective literals. An objective literal is either an atom A or its negation —iA where -i is one kind of negation introduced. The symbol not stands for negation by default, an additional kind of negation. notL is termed a default literal. Literals are either objective or default ones. By the language of P, £{P) wc mean the set of all ground literals built from the symbols occuring in P. Whenever unambigous we refer ...
In this paper we define the rather general framework of Monotonic Logic Programs, where the main ... more In this paper we define the rather general framework of Monotonic Logic Programs, where the main results of (definite) logic programming are validly extrapolated. Whenever defining new logic programming extensions, we can thus turn our attention to the stipulation and study of its intuitive algebraic properties within the very general setting. Then, the existence of a minimum model and of a monotonic immediate consequences operator is guaranteed, and they are related as in classical logic programming. Afterwards we study the more restricted class of residuated logic programs which is able to capture several quite distinct logic programming semantics. Namely: Generalized Annotated Logic Programs, Fuzzy Logic Programming, Hybrid Probabilistic Logic Programs, and Possibilistic Logic Programming. We provide the embedding of possibilistic logic programming.
The aim of this paper is to combine, into a single logic programming framework, the hitherto sepa... more The aim of this paper is to combine, into a single logic programming framework, the hitherto separate forms of reasoning of preferences and updating. More precisely, we define a language capable of considering sequences of logic programs that result from the consecutive updates of an initial program, where it is possible to define a priority relation among the rules of all successive programs. Moreover, within the framework, the priority relation can itself be updated. In order to define a declarative semantics for the language, we start by reviewing the declarative semantics of updates of [1], and by presenting a definition of a semantics for preferences, shown equivalent to the one in [5], in a form suitable for its integration with the updates one. Before the conclusions and mention of future work, we present two illustrative examples of application of the framework.
Most of the work conducted so far in the field of logic programming has focused on representing s... more Most of the work conducted so far in the field of logic programming has focused on representing static knowledge, i.e. knowledge that does not evolve with time. To overcome this limitation, in a recent paper, the authors introduced the concept of dynamic logic programming. There, they studied and defined the declarative and operational semantics of sequences of logic programs (or dynamic logic programs), P0 ⊕...⊕Pn. Each such program contains knowledge about some given state, where different states may, e.g., represent different time periods or different sets of priorities. The role of dynamic logic programming is to employ relationships existing between the possibly mutually contradictory sequence of programs to precisely determine, at any given state, the declarative and procedural semantics of their combination. But how, in concrete situations, is a sequence of logic programs built? For instance, in the domain of actions, what are the appropriate sequences of programs that represent the performed actions and their effects? Whereas dynamic logic programming provides a way for determining what should follow, given the sequence of programs, it does not provide a good practical language for the specification of updates or changes in the knowledge represented by successive logic programs. In this paper we define a language designed for specifying changes to logic programs (LUPS - “Language for dynamic updates”). Given an initial knowledge base (in the form of a logic program) LUPS provides a way for sequentially updating it. The declarative meaning of a sequence of sets of update actions in LUPS is defined using the semantics of the dynamic logic program generated by those actions. We also provide a translation of the sequence of update statements sets into a single generalized logic program written in a meta-language, so that the stable models of the resulting program correspond to the previously defined declarative semantics. This meta-language is used in the actual implementation, although his is not the subject of this paper. Finally we briefly mention related work (lack of space prevents us from presenting more detailed comparisons).
Next we oenne tne program transformation 11/M (11 modulo M), which is a 3-valued extension to the... more Next we oenne tne program transformation 11/M (11 modulo M), which is a 3-valued extension to the 2-valued transformation in [Gelfond and Lifschitz, 1988]. Definition 2.4 Let H be a logic program and let I be a 3-valued interpretation. By the extended GL- tmnsformation of H modulo I we mean a new (nonnegative) program H / I obtained from H by performing the following three operations: 0 Removing from H all rules which contain a negative premise L =~A such that = 0. 0 Replacing in all remaining rules those negative premises L =~A which satisfy : 1/2 by ...
In this paper we i n v estigate updates of knowledge bases represented by logic programs. In orde... more In this paper we i n v estigate updates of knowledge bases represented by logic programs. In order to represent negative information, we use generalized logic programs which allow default negation not only in rule bodies but also in their heads.We start by introducing the notion of an update P U of a logic program P by another logic program U. Subsequently, w e provide a precise semantic characterization of P U, and study some basic properties of program updates. In particular, we show that our update programs generalize the notion of interpretation update. We then extend this notion to compositional sequences of logic programs updates P 1 P 2 : : : , de ning a dynamic program update, and thereby i n troducing the paradigm of dynamic logic programming. This paradigm signicantly facilitates modularization of logic programming, and thus modularization of nonmonotonic reasoning as a whole. Speci cally, suppose that we are given a set of logic program modules, each describing a di erent state of our knowledge of the world. Di erent states may represent di erent time points or di erent sets of priorities or perhaps even di erent viewpoints. Consequently, program modules may contain mutually contradictory as well as overlapping information. The role of the dynamic program update is to employ the mutual relationships existing between di erent modules to precisely determine, at any given module composition stage, the declarative a s w ell as the procedural semantics of the combined program resulting from the modules.
A debugger for Prolog has been developed which automates the reasoning ability required to pinpoi... more A debugger for Prolog has been developed which automates the reasoning ability required to pinpoint errors, resorting to the user only to ask about the intended program semantics, and making cooperative use of the declarative and the operational semantics. The algorithm is expressed in detail, a session protocol exhibited, comparison to other work made, but the implementation is not examined, nor the treatment of Prolog's extra-logical features. This is an abridged version of [Pereira 86].
Abstract Our purpose is to define a semantics that extends Well Founded Semantics for programs wi... more Abstract Our purpose is to define a semantics that extends Well Founded Semantics for programs with classical negation, and which avoids the absence of models caused by contradictions brought about by closed world assumptions. This extension relics on allowing to take back such closed world assumptions, through making their truth value become undefined, and thus pcrmiting noncontradictory models to appear. We take back such assumptions in a minimal way for all alternative ways of removing contradictions, by ...
In this paper we investigate updates of knowledge bases represented by logic programs. In order t... more In this paper we investigate updates of knowledge bases represented by logic programs. In order to represent negative information, we use generalized logic programs which allow default negation not only in rule bodies but also in their heads. We start by introducing the notion of an update P È U of one logic program P by another logic program U. Subsequently, we provide a precise semantic characterization of P È U , and study some basic properties of program updates. In particular, we show that our update programs generalize the notion of interpretation update. We then extend this notion to compositional sequences of logic programs updates P 1 È P 2 È Á Á Á Y de®ning a dynamic program update, and thereby introducing the paradigm of dynamic logic programming. This paradigm signi®cantly facilitates modularization of logic programming, and thus modularization of non-monotonic reasoning as a whole. Speci®cally, suppose that we are given a set of logic program modules, each describing a dierent state of our knowledge of the world. Dierent states may represent dierent time points or dierent sets of priorities or perhaps even dierent viewpoints. Consequently, program modules may contain mutually contradictory as well as overlapping information. The role of the dynamic program update is to employ the mutual relationships existing between dierent modules to precisely determine, at any given module composition stage, the declarative as well as the procedural semantics of the combined program resulting from the modules. Ó
The evolution of logic programming semantics has included the introduction of a new explicit form... more The evolution of logic programming semantics has included the introduction of a new explicit form of negation, beside the older implicit (or default) negation typical of logic programming. The richer language has been shown adequate for a spate of knowledge representation and reasoning forms. The widespread use of such extended programs requires the definition of a correct top-down querying mechanism, much as for Prolog wrt. normal programs. One purpose of this paper is to present and exploit a SLDNF-like derivation procedure, SLX, for programs with explicit negation under well-founded semantics (WFSX) and prove its soundness and completeness. (Its soundness wrt. the answer-sets semantics is also shown.) Our choice ofWFSX as the base semantics is justi-fied by the structural properties it enjoys, which are paramount for top-down query evaluation. Of course, introducing explicit negation requires dealing with contradiction. Consequently, we allow for contradiction to appear, and show moreover how it can be removed by freely changing the truth-values of some subset of a set of predefined revisable literals. To achieve this, we introduce a paraconsistent version ofWFSX, WFSX p , that allows contradictions and for which our SLX top-down procedure is proven correct as well. This procedure can be used to detect the existence of pairs of complementary literals inWESX p simply by detecting the violation of integrity rulesf ←L, -L introduced for eachL in the language of the program. Furthermore, integrity constraints of a more general form are allowed, whose violation can likewise be detected by SLX. Removal of contradiction or integrity violation is accomplished by a variant of the SLX procedure that collects, in a formula, the alternative combinations of revisable literals' truth-values that ensure the said removal. The formulas, after simplification, can then be satisfied by a number of truth-values changes in the revisable, among “true,” “false”, and “undefined”. A notion of minimal change is defined as well that establishes a closeness relation between a program and its revisions. Forthwith, the changes can be enforced by introducing or deleting program rules for the revisable literals. To illustrate the usefulness and originality of our framework, we applied it to obtain a novel logic programming approach, and results, in declarative debugging and model-based diagnosis problems.
The use of water for agricultural production in water scarcity regions requires innovative and su... more The use of water for agricultural production in water scarcity regions requires innovative and sustainable research, and an appropriate transfer of technologies. This paper discusses some of these aspects, mainly relative to on-farm irrigation management including the use of treated wastewater and saline waters. First, the paper proposes some concepts relative to water scarcity, concerning aridity, drought, deserti®cation and water shortage, as well as policies to cope with these water stressed regimes. Conceptual approaches on irrigation performances, water use and water savings are reviewed in a wide perspective. This is followed by a discussion of supply management to cope with water scarcity, giving particular attention to the use of wastewater and low-quality waters, including the respective impacts on health and the environment as water scarcity is requiring that waters of inferior quality be increasingly used for irrigation. The paper then focuses on demand management, starting with aspects relating to the improvement of irrigation methods and the respective performances, mainly the distribution uniformity (DU) as a fundamental tool to reduce the demand for water at the farm level, and to control the negative environmental impacts of over-irrigation, including salt stressed areas. Discussions are supported by recent research results. The suitability of irrigation methods for using treated wastewaters and saline waters is analysed. Supplemental irrigation (SI) and de®cit irrigation strategies are also discussed, including limitations on the applicability of related practices. The paper also identi®es the need to adopt emerging technologies for water management as well as to develop appropriate methodologies for the analysis of social, economic, and environmental bene®ts of improved irrigation management. #
The use of traditional backtracking to explore a search space top-down starts with the initial st... more The use of traditional backtracking to explore a search space top-down starts with the initial state as the current state. Then, for each forward derivation step, one of the operators applicable to the current state is used to derive a new current state. This forward execution is repeated until either a solution state is reached and success is reported, or the set ofuriused operators applicable to the current state is empty. At this point, the search backtracks. The current state is dropped, its predecessor is reinstated as the current state, and forward ...
Wide-bandgap high-mobility ZnO thin-film transistors produced at room temperature. [Applied Physi... more Wide-bandgap high-mobility ZnO thin-film transistors produced at room temperature. [Applied Physics Letters 85, 2541 (2004)]. Elvira MC Fortunato, Pedro MC Barquinha, Ana CMBG Pimentel, Alexandra MF Gonçalves, António JS Marques, Rodrigo FP Martins, Luis MN Pereira. ...
Functional oxide materials currently represent a key challenge as well as a promising powerful to... more Functional oxide materials currently represent a key challenge as well as a promising powerful tool for both fundamental understanding and technological development of the next generation of transparent electronics, such as field-effect transistors. Here, we report a fully transparent ZnO thin-film transistor (ZnO-TFT) with a transmittance above 80 % in the visible part of the spectrum, including the glass substrate, fabricated by radiofrequency (rf) magnetron sputtering at room temperature, with a bottom gate configuration. The ZnO-TFT operates in the enhancement mode, exhibiting a high saturation mobility of about 20 cm 2 V ±1 s ±1 , a threshold voltage of 21 V, a gate-voltage swing of 1.24 V decade ±1 , and an on/off ratio of 2 10 5 . Besides this, the off resistance is on the order of 20 MX and the on resistance is on the order of 45 kX. The combination of transparency, high mobility, and room-temperature processing makes the ZnO-TFT a very promising lowcost optoelectronic device for the next generation of invisible and flexible electronics, such as switching for addressing active matrices based on organic light-emitting diodes (OLEDs).
The agent paradigm, commonly implemented by means of imperative languages mainly for reasons of e... more The agent paradigm, commonly implemented by means of imperative languages mainly for reasons of efficiency, has recently increased its influence in the research and development of computational logic based systems. Since efficiency is not always the crucial issue, but clear specification and correctness is, Logic Programming and Non-monotonic Reasoning have been brought back into the spotlight. To this accrues the recent significant improvements in the efficiency of Logic Programming implementations for Non-monotonic Reasoning. This paper presents an overall description of MIN ERVA, an agent architecture and system designed with the intention of providing a common agent framework based on the unique strengths of Logic Programming, to allow for the combination of several non-monotonic knowledge representation and reasoning mechanisms developed in recent years. In [10], the semantics of the multi-dimensional structure and combination of the evolving societal knowledge of agents in described and discussed in detail.
Abstract Well Founded Semantics is adequate to capture nonmonotonic reasoning if we interpret the... more Abstract Well Founded Semantics is adequate to capture nonmonotonic reasoning if we interpret the Well Founded model of a program P as a (possibly incomplete) view of the world. Thus the Well Founded model may be accepted to be a definite view of the world and the extended stable models as alternative enlarged consistent belief models an agent may have about the world. Our purpose is to exhibit a modular systematic method of representing nonmonotonic problems with the Well Founded semantics of logic programs. In this paper ...
Recently the field of theory update has seen some improvement, in what concerns model updating, b... more Recently the field of theory update has seen some improvement, in what concerns model updating, by allowing updates to be specified by so-called revision programs. The updating of theory models is governed by their update rules and also by inertia applied to those literals not directly affected by the update program. Though this is important, it remains necessary to tackle as well the updating of programs specifying theories. Some results have been obtained on the issue of updating a logic program which encodes a set of models, to obtain a new program whose models are the desired updates of the initial models. But here the program only plays the rÔle of a means to encode the models. A logic program encodes much more than a set of models: it encodes knowledge in the form of the relationships between the elements of those models. In this paper we advocate that the principle of inertia is advantageously applied to the rules of the initial program rather than to the individual literals in a model. Indeed, we show how this concept of program update generalizes model or interpretation updates. Furthermore, it allows us to conceive what it is to update one program by another, a crucial notion for opening up a whole new range of applications concerning the evolution of knowledge bases. We will consider the updating of normal programs as well as these extended with explicit negation, under the stable semantics.
This paper reports on the use of logic program updates to models actions that bring about changes... more This paper reports on the use of logic program updates to models actions that bring about changes in knowledge states describing the world and its rules. The LUPS language is employed to specify concurrent update rules to model actions that depend on, and change, rule rich world states, not described simply by propositional uents. This language and corresponding semantics, whose original stable semantics we generalize to the well-founded setting, is brie y recapitulated here.
1 Language An extended logic program (or x-program) P is a set of rules of the form: H &a... more 1 Language An extended logic program (or x-program) P is a set of rules of the form: H <— Bi,... ,Bn, not Ci,... ,not Cm where n,m > 0 and H,B.¡,Ci arc objective literals. An objective literal is either an atom A or its negation —iA where -i is one kind of negation introduced. The symbol not stands for negation by default, an additional kind of negation. notL is termed a default literal. Literals are either objective or default ones. By the language of P, £{P) wc mean the set of all ground literals built from the symbols occuring in P. Whenever unambigous we refer ...
In this paper we define the rather general framework of Monotonic Logic Programs, where the main ... more In this paper we define the rather general framework of Monotonic Logic Programs, where the main results of (definite) logic programming are validly extrapolated. Whenever defining new logic programming extensions, we can thus turn our attention to the stipulation and study of its intuitive algebraic properties within the very general setting. Then, the existence of a minimum model and of a monotonic immediate consequences operator is guaranteed, and they are related as in classical logic programming. Afterwards we study the more restricted class of residuated logic programs which is able to capture several quite distinct logic programming semantics. Namely: Generalized Annotated Logic Programs, Fuzzy Logic Programming, Hybrid Probabilistic Logic Programs, and Possibilistic Logic Programming. We provide the embedding of possibilistic logic programming.
The aim of this paper is to combine, into a single logic programming framework, the hitherto sepa... more The aim of this paper is to combine, into a single logic programming framework, the hitherto separate forms of reasoning of preferences and updating. More precisely, we define a language capable of considering sequences of logic programs that result from the consecutive updates of an initial program, where it is possible to define a priority relation among the rules of all successive programs. Moreover, within the framework, the priority relation can itself be updated. In order to define a declarative semantics for the language, we start by reviewing the declarative semantics of updates of [1], and by presenting a definition of a semantics for preferences, shown equivalent to the one in [5], in a form suitable for its integration with the updates one. Before the conclusions and mention of future work, we present two illustrative examples of application of the framework.
Most of the work conducted so far in the field of logic programming has focused on representing s... more Most of the work conducted so far in the field of logic programming has focused on representing static knowledge, i.e. knowledge that does not evolve with time. To overcome this limitation, in a recent paper, the authors introduced the concept of dynamic logic programming. There, they studied and defined the declarative and operational semantics of sequences of logic programs (or dynamic logic programs), P0 ⊕...⊕Pn. Each such program contains knowledge about some given state, where different states may, e.g., represent different time periods or different sets of priorities. The role of dynamic logic programming is to employ relationships existing between the possibly mutually contradictory sequence of programs to precisely determine, at any given state, the declarative and procedural semantics of their combination. But how, in concrete situations, is a sequence of logic programs built? For instance, in the domain of actions, what are the appropriate sequences of programs that represent the performed actions and their effects? Whereas dynamic logic programming provides a way for determining what should follow, given the sequence of programs, it does not provide a good practical language for the specification of updates or changes in the knowledge represented by successive logic programs. In this paper we define a language designed for specifying changes to logic programs (LUPS - “Language for dynamic updates”). Given an initial knowledge base (in the form of a logic program) LUPS provides a way for sequentially updating it. The declarative meaning of a sequence of sets of update actions in LUPS is defined using the semantics of the dynamic logic program generated by those actions. We also provide a translation of the sequence of update statements sets into a single generalized logic program written in a meta-language, so that the stable models of the resulting program correspond to the previously defined declarative semantics. This meta-language is used in the actual implementation, although his is not the subject of this paper. Finally we briefly mention related work (lack of space prevents us from presenting more detailed comparisons).
Next we oenne tne program transformation 11/M (11 modulo M), which is a 3-valued extension to the... more Next we oenne tne program transformation 11/M (11 modulo M), which is a 3-valued extension to the 2-valued transformation in [Gelfond and Lifschitz, 1988]. Definition 2.4 Let H be a logic program and let I be a 3-valued interpretation. By the extended GL- tmnsformation of H modulo I we mean a new (nonnegative) program H / I obtained from H by performing the following three operations: 0 Removing from H all rules which contain a negative premise L =~A such that = 0. 0 Replacing in all remaining rules those negative premises L =~A which satisfy : 1/2 by ...
In this paper we i n v estigate updates of knowledge bases represented by logic programs. In orde... more In this paper we i n v estigate updates of knowledge bases represented by logic programs. In order to represent negative information, we use generalized logic programs which allow default negation not only in rule bodies but also in their heads.We start by introducing the notion of an update P U of a logic program P by another logic program U. Subsequently, w e provide a precise semantic characterization of P U, and study some basic properties of program updates. In particular, we show that our update programs generalize the notion of interpretation update. We then extend this notion to compositional sequences of logic programs updates P 1 P 2 : : : , de ning a dynamic program update, and thereby i n troducing the paradigm of dynamic logic programming. This paradigm signicantly facilitates modularization of logic programming, and thus modularization of nonmonotonic reasoning as a whole. Speci cally, suppose that we are given a set of logic program modules, each describing a di erent state of our knowledge of the world. Di erent states may represent di erent time points or di erent sets of priorities or perhaps even di erent viewpoints. Consequently, program modules may contain mutually contradictory as well as overlapping information. The role of the dynamic program update is to employ the mutual relationships existing between di erent modules to precisely determine, at any given module composition stage, the declarative a s w ell as the procedural semantics of the combined program resulting from the modules.
A debugger for Prolog has been developed which automates the reasoning ability required to pinpoi... more A debugger for Prolog has been developed which automates the reasoning ability required to pinpoint errors, resorting to the user only to ask about the intended program semantics, and making cooperative use of the declarative and the operational semantics. The algorithm is expressed in detail, a session protocol exhibited, comparison to other work made, but the implementation is not examined, nor the treatment of Prolog's extra-logical features. This is an abridged version of [Pereira 86].
Abstract Our purpose is to define a semantics that extends Well Founded Semantics for programs wi... more Abstract Our purpose is to define a semantics that extends Well Founded Semantics for programs with classical negation, and which avoids the absence of models caused by contradictions brought about by closed world assumptions. This extension relics on allowing to take back such closed world assumptions, through making their truth value become undefined, and thus pcrmiting noncontradictory models to appear. We take back such assumptions in a minimal way for all alternative ways of removing contradictions, by ...
In this paper we investigate updates of knowledge bases represented by logic programs. In order t... more In this paper we investigate updates of knowledge bases represented by logic programs. In order to represent negative information, we use generalized logic programs which allow default negation not only in rule bodies but also in their heads. We start by introducing the notion of an update P È U of one logic program P by another logic program U. Subsequently, we provide a precise semantic characterization of P È U , and study some basic properties of program updates. In particular, we show that our update programs generalize the notion of interpretation update. We then extend this notion to compositional sequences of logic programs updates P 1 È P 2 È Á Á Á Y de®ning a dynamic program update, and thereby introducing the paradigm of dynamic logic programming. This paradigm signi®cantly facilitates modularization of logic programming, and thus modularization of non-monotonic reasoning as a whole. Speci®cally, suppose that we are given a set of logic program modules, each describing a dierent state of our knowledge of the world. Dierent states may represent dierent time points or dierent sets of priorities or perhaps even dierent viewpoints. Consequently, program modules may contain mutually contradictory as well as overlapping information. The role of the dynamic program update is to employ the mutual relationships existing between dierent modules to precisely determine, at any given module composition stage, the declarative as well as the procedural semantics of the combined program resulting from the modules. Ó
The evolution of logic programming semantics has included the introduction of a new explicit form... more The evolution of logic programming semantics has included the introduction of a new explicit form of negation, beside the older implicit (or default) negation typical of logic programming. The richer language has been shown adequate for a spate of knowledge representation and reasoning forms. The widespread use of such extended programs requires the definition of a correct top-down querying mechanism, much as for Prolog wrt. normal programs. One purpose of this paper is to present and exploit a SLDNF-like derivation procedure, SLX, for programs with explicit negation under well-founded semantics (WFSX) and prove its soundness and completeness. (Its soundness wrt. the answer-sets semantics is also shown.) Our choice ofWFSX as the base semantics is justi-fied by the structural properties it enjoys, which are paramount for top-down query evaluation. Of course, introducing explicit negation requires dealing with contradiction. Consequently, we allow for contradiction to appear, and show moreover how it can be removed by freely changing the truth-values of some subset of a set of predefined revisable literals. To achieve this, we introduce a paraconsistent version ofWFSX, WFSX p , that allows contradictions and for which our SLX top-down procedure is proven correct as well. This procedure can be used to detect the existence of pairs of complementary literals inWESX p simply by detecting the violation of integrity rulesf ←L, -L introduced for eachL in the language of the program. Furthermore, integrity constraints of a more general form are allowed, whose violation can likewise be detected by SLX. Removal of contradiction or integrity violation is accomplished by a variant of the SLX procedure that collects, in a formula, the alternative combinations of revisable literals' truth-values that ensure the said removal. The formulas, after simplification, can then be satisfied by a number of truth-values changes in the revisable, among “true,” “false”, and “undefined”. A notion of minimal change is defined as well that establishes a closeness relation between a program and its revisions. Forthwith, the changes can be enforced by introducing or deleting program rules for the revisable literals. To illustrate the usefulness and originality of our framework, we applied it to obtain a novel logic programming approach, and results, in declarative debugging and model-based diagnosis problems.
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