SNePS
Encyclopedia
SNePS is a knowledge representation
, reasoning, and acting (KRRA) system developed and maintained by Stuart C. Shapiro and colleagues at the State University of New York at Buffalo.
SNePS is simultaneously a logic
-based, frame
-based, and network
-based KRRA system. It uses an assertional model of knowledge, in that a SNePS knowledge base (KB) consists of a set of assertions (propositions) about various entities. Its intended model is of an intensional
domain of mental entities---the entities conceived of by some agent, and the propositions believed by it. The intensionality is primarily accomplished by the absence of a built-in equality operator, since any two syntactically different terms might have slightly different Fregean senses
.
SNePS has three styles of inference: formula-based, derived from its logic-based personality; slot-based, derived from its frame-based personality; and path-based, derived from its network-based personality. However, all three are integrated, operating together.
SNePS may be used as a stand-alone KRR system. It has also been used, along with its integrated acting component, to implement the mind of intelligent agent
s (cognitive robots
), in accord with the GLAIR agent architecture (a layered cognitive architecture
). The SNePS Research Group often calls its agents Cassie.
Formula-based inference is implemented as a natural-deduction-style inference engine in which there are introduction and elimination rules for the connectives and quantifiers. SNePS formula-based inference is sound but not complete, as rules of inference that are less useful for natural language understanding and commonsense reasoning have not been implemented.
A proposition-denoting term in a SNePS KB might or might not be "asserted", that is, treated as true in the KB. The SNePS logic is a paraconsistent version of Relevance Logic, so that a contradiction does not imply anything whatsoever. Nevertheless, SNeBR, the SNePS Belief Revision subsystem, will notice any explicit contradiction and engage the user in a dialogue to repair it. SNeBR is an Assumption-Based Truth Maintenance System (ATMS), and removes the assertion status of any proposition whose support has been removed.
SNePSLOG may be used in any of three modes. In two modes, the caseframe (set of slots) associated with each functional term is determined by the system. In mode 3, the user declares what caseframe is to be used for each function symbol.
In slot-based inference, any proposition-valued frame is considered to imply the frame with any of its slots filled by a subset of its fillers. In the current implementation, this is not always sound.
,
thus the original meaning of "SNePS" as "The Semantic Network
Processing System". This view is obtained by considering every
individual constant and every functional term to be a node of the
network, and every slot to be a directed labeled arc from the
frame-node it is in to every node in its filler. In the intended
interpretation, every node denotes a mental entity, some of which are
propositions, and every proposition represented in the network is
represented by the node that denotes it. Some nodes are variables of
the SNePS logic, and they range over nodes, and only over nodes.
Path-based inference rules may be defined, although they, themselves,
are not represented in SNePS. A path-based inference rule specifies
that some labeled arc r may be inferred as present from some node n
to some other node m just in case a given path exists from n to m.
There is an extensive recursive set of path constructors available.
understanding and generation
, for commonsense reasoning
, and for
cognitive robotics
. It has been used in several KR courses around the
world.
and is freely available.
Knowledge representation
Knowledge representation is an area of artificial intelligence research aimed at representing knowledge in symbols to facilitate inferencing from those knowledge elements, creating new elements of knowledge...
, reasoning, and acting (KRRA) system developed and maintained by Stuart C. Shapiro and colleagues at the State University of New York at Buffalo.
SNePS is simultaneously a logic
Logic
In philosophy, Logic is the formal systematic study of the principles of valid inference and correct reasoning. Logic is used in most intellectual activities, but is studied primarily in the disciplines of philosophy, mathematics, semantics, and computer science...
-based, frame
Frame language
A frame language is a metalanguage. It applies the frame concept to the structuring of language properties. Frame languages are usually software languages.-Description:...
-based, and network
Semantic network
A semantic network is a network which represents semantic relations among concepts. This is often used as a form of knowledge representation. It is a directed or undirected graph consisting of vertices, which represent concepts, and edges.- History :...
-based KRRA system. It uses an assertional model of knowledge, in that a SNePS knowledge base (KB) consists of a set of assertions (propositions) about various entities. Its intended model is of an intensional
Intensional
Intensional* in philosophy of language: not extensional. See also intensional definition versus extensional definition.* in philosophy of mind: an intensional state is a state which has a propositional content....
domain of mental entities---the entities conceived of by some agent, and the propositions believed by it. The intensionality is primarily accomplished by the absence of a built-in equality operator, since any two syntactically different terms might have slightly different Fregean senses
Sense and reference
Sinn and bedeutung are usually translated, respectively, as sense and reference. Two different aspects of some terms' meanings, a term's reference is the object that the term refers to, while the term's sense is the way that the term refers to that object.Sinn and bedeutung were introduced by...
.
SNePS has three styles of inference: formula-based, derived from its logic-based personality; slot-based, derived from its frame-based personality; and path-based, derived from its network-based personality. However, all three are integrated, operating together.
SNePS may be used as a stand-alone KRR system. It has also been used, along with its integrated acting component, to implement the mind of intelligent agent
Intelligent agent
In artificial intelligence, an intelligent agent is an autonomous entity which observes through sensors and acts upon an environment using actuators and directs its activity towards achieving goals . Intelligent agents may also learn or use knowledge to achieve their goals...
s (cognitive robots
Cognitive robotics
a robot is a robot device that is built from inanimate matter. Its behavior in response to the environment is deterministic, based on how the robot was designed. Cognition is the process of acquiring and using knowledge about the world for goal-oriented purposes, such as survival...
), in accord with the GLAIR agent architecture (a layered cognitive architecture
Agent architecture
Agent architecture in computer science is a blueprint for software agents and intelligent control systems, depicting the arrangement of components...
). The SNePS Research Group often calls its agents Cassie.
SNePS as a Logic-Based System
As a logic-based system, a SNePS KB consists of a set of terms, and functions and formulas over those terms. The set of logical connectives and quantifiers extends the usual set used by first-order logics, all taking one or more arbitrarily-sized sets of arguments. In accord with the intended use of SNePS to represent the mind of a natural-language-competent intelligent agent, propositions are first-class entities of the intended domain, so formulas are actually proposition-denoting functional terms. SNePSLOG, the input-output language of the logic-based face of SNePS, looks like a naive logic in that function symbols (including "predicates"), and formulas (actually proposition-denoting terms) may be the arguments of functions and may be quantified over. The underlying SNePS, however, is a first order logic, with the user's function symbols and formulas reified.Formula-based inference is implemented as a natural-deduction-style inference engine in which there are introduction and elimination rules for the connectives and quantifiers. SNePS formula-based inference is sound but not complete, as rules of inference that are less useful for natural language understanding and commonsense reasoning have not been implemented.
A proposition-denoting term in a SNePS KB might or might not be "asserted", that is, treated as true in the KB. The SNePS logic is a paraconsistent version of Relevance Logic, so that a contradiction does not imply anything whatsoever. Nevertheless, SNeBR, the SNePS Belief Revision subsystem, will notice any explicit contradiction and engage the user in a dialogue to repair it. SNeBR is an Assumption-Based Truth Maintenance System (ATMS), and removes the assertion status of any proposition whose support has been removed.
SNePS as a Frame-Based System
As a frame-based system, every SNePS functional term (including proposition-valued terms) is represented by a frame with slots and fillers. Each slot may be filled by an arbitrarily-sized set of other terms. However, cycles cannot be constructed. SNePSUL, the SNePS User Language is an input-output language for interacting with SNePS in its guise as a frame-based system.SNePSLOG may be used in any of three modes. In two modes, the caseframe (set of slots) associated with each functional term is determined by the system. In mode 3, the user declares what caseframe is to be used for each function symbol.
In slot-based inference, any proposition-valued frame is considered to imply the frame with any of its slots filled by a subset of its fillers. In the current implementation, this is not always sound.
SNePS as a Network-Based System
As a network-based system, SNePS is a propositional semantic networkSemantic network
A semantic network is a network which represents semantic relations among concepts. This is often used as a form of knowledge representation. It is a directed or undirected graph consisting of vertices, which represent concepts, and edges.- History :...
,
thus the original meaning of "SNePS" as "The Semantic Network
Processing System". This view is obtained by considering every
individual constant and every functional term to be a node of the
network, and every slot to be a directed labeled arc from the
frame-node it is in to every node in its filler. In the intended
interpretation, every node denotes a mental entity, some of which are
propositions, and every proposition represented in the network is
represented by the node that denotes it. Some nodes are variables of
the SNePS logic, and they range over nodes, and only over nodes.
Path-based inference rules may be defined, although they, themselves,
are not represented in SNePS. A path-based inference rule specifies
that some labeled arc r may be inferred as present from some node n
to some other node m just in case a given path exists from n to m.
There is an extensive recursive set of path constructors available.
Components
- SNIP, the SNePS Inference Package, provides the rules of inference with which SNePS deduces new assertions from an existing KB.
- SNeBR, the SNePS Belief RevisionBelief revisionBelief revision is the process of changing beliefs to take into account a new piece of information. The logical formalization of belief revision is researched in philosophy, in databases, and in artificial intelligence for the design of rational agents....
package, is a component of SNePS that detects when the KB contains contradictory beliefs. When a contradiction is detected, the user is encouraged to unassert one of the contradictory beliefs by unasserting some underlying hypotheses that led to the contradiction. As a result, all propositions that had been inferred from the hypotheses that have been unasserted are also unasserted.
- SNeRE, the SNePS Rational Engine, provides an acting executive and a set of frames for building up complex acts and plans from a set of system-defined and user-defined primitive actions. System-defined frames allow for the specification of sequences of acts, conditional acts, and iteration over acts, as well as believing and disbelieving propositions. SNeRE policies connect acting to inference, specifying, for example, that a certain act is to be done when a certain proposition is believed (asserted).
- SNaLPS, the SNePS Natural Language Processing System, consists of a Generalized Augmented Transition NetworkAugmented transition networkAn augmented transition network is a type of graph theoretic structure used in the operational definition of formal languages, used especially in parsing relatively complex natural languages, and having wide application in artificial intelligence...
Grammar interpreter and an English morphological analyzerMorphological analysisMorphological Analysis or General Morphological Analysis is a method developed by Fritz Zwicky for exploring all the possible solutions to a multi-dimensional, non-quantified problem complex.-Overview:...
and synthesizer so that natural language understanding and generation may be provided for SNePS-based agents.
Applications
SNePS has been used for a variety of KRR tasks, for natural languageunderstanding and generation
Natural language processing
Natural language processing is a field of computer science and linguistics concerned with the interactions between computers and human languages; it began as a branch of artificial intelligence....
, for commonsense reasoning
Commonsense reasoning
Commonsense reasoning is the branch of Artificial intelligence concerned with replicating human thinking. There are several components to this problem, including:* Developing adequately broad and deep commonsense knowledge bases....
, and for
cognitive robotics
Cognitive robotics
a robot is a robot device that is built from inanimate matter. Its behavior in response to the environment is deterministic, based on how the robot was designed. Cognition is the process of acquiring and using knowledge about the world for goal-oriented purposes, such as survival...
. It has been used in several KR courses around the
world.
Availability
SNePS is implemented as a platform-independent system in Common LispCommon Lisp
Common Lisp, commonly abbreviated CL, is a dialect of the Lisp programming language, published in ANSI standard document ANSI INCITS 226-1994 , . From the ANSI Common Lisp standard the Common Lisp HyperSpec has been derived for use with web browsers...
and is freely available.