Baral C, Gelfond M. Reasoning about effects of concurrent actions. Journal of Logic Programming 1997; 31:85-118.  Home/Search   Document Details and Download   Summary   Related Articles   Check

....) denotes the fact that state s is a possible result of executing action a on state s. The tuples ( s , a, s ) define the possible state transitions associated with the agent actions. Different languages can be used to specify these transitions. For example, STRIPS ( Fikes and Nilsson, 1971] Ac ([Baral and Gelfond, 1997]) C ( Giunchiglia and Lifschitz, 1998] Definition A. 1 is akin to the one given by Bacchus, Halpern and Levesque in the context of reasoning about knowledge in the situation calculus ( Bacchus et al. 1999] page 182) They in turn draw in Moore s work [Moore, 1979, Moore, 1985] on using ....

Chitta Baral and Michael Gelfond. Reasoning about effects of concurrent actions. Journal of Logic Programming, 31(1-3):85-117, 1997.

....the fact that state s is a possible result of executing action a on state s. The tuples # s ;a;s # define the possible state transitions associated with the agent actions. Different languages can be used to specify these transitions. For example, STRIPS ( Fikes and Nilsson, 1971] A# ([Baral and Gelfond, 1997] ) C ( Giunchiglia and Lifschitz, 1998] Definition A.1 is akin to the one given by Bacchus, Halpern and Levesque in the context of reasoning about knowledge in the situation calculus ( Bacchus et al. 1999] page 182) They in turn draw in Moore s work [Moore, 1979, Moore, 1985] on using ....

Chitta Baral and Michael Gelfond. Reasoning about effects of concurrent actions. Journal of Logic Programming, 31(1-3):85--117, 1997.

....pos with range f0; 1; 2; 3g. The (Lift Block,Hit Robot) and (Lower Block,Hit Robot) joint actions are drawn with solid and dashed arrows respectively. States marked with I and G are initial and goal states. 12, 31] Our joint action representation has more resemblance with A C and C [2, 24], where sets of actions are performed at each time step. In contrast to these approaches, though, we model multi agent domains. An important issue to address when introducing concurrent actions is synergetic effects between simultaneously executing actions [33] A common example of destructive ....

....are interfering and cannot be performed concurrently. The current version of NADL only avoids destructive synergetic effects. It does not include ways of representing constructive synergetic effects between simultaneous acting agents [33] A constructive synergetic effect is illustrated in [2], where an agent spills soup from a bowl when trying to lift it up with one hand, but not when lifting it up with both hands. In C and A C this kind of synergetic effects can be represented by explicitly stating the effect of a compound action. A similar approach could be used in NADL, but is ....

C. Baral and M. Gelfond. Reasoning about effects of concurrent actions. The Journal of Logic Programming, pages 85--117, 1997.

....effect rules. Pinto shows how such causal rules should be translated in his framework using delayed actions. In our approach, these causal rules can be represented directly in the formalism. It would be interesting to further investigate the relation between both approaches in the future. In [4], Baral and Gelfond define the language A c to extend A with action qualifications and concurrent actions. The semantics of A c is defined through a transition function, which maps tuples consisting of a state and a set of concurrent actions to a new state; our transition function is of a similar ....

....and Gelfond define the language A c to extend A with action qualifications and concurrent actions. The semantics of A c is defined through a transition function, which maps tuples consisting of a state and a set of concurrent actions to a new state; our transition function is of a similar sort. [4] expresses the effects in the soup bowl example as follows: lift l causes spilled lift r causes spilled flift l ; lift r g causes :spilled if :spilled For a set of concurrent actions including lift l ; lift r , the third rule overrides the two effect rules of the individual actions lift r and ....

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C. Baral and M. Gelfond. Reasoning about effects of concurrent actions. Journal of Logic Programming, 31:85--118, 1997.

.... Representation of concurrent actions has been dealt with by various researchers in the knowledge representation community (e.g. Lin Shoham, 1992; Reiter, 1996; de Giacomo, L esperance, Levesque, 1997; Moses Tennenholtz, 1995; Pinto, 1998) Of particular note are the action languages A c (Baral Gelfond, 1997) and C (Giunchiglia Lifschitz, 1998) which enable the specification of concurrent interacting actions and employ a nonmonotonic override mechanism to deduce the effects of a set of actions with conflicting effects. Finally, a number of contemporary planners can handle concurrent noninteracting ....

....fact, we believe that certain nonconcurrency constraints are more naturally described using such a resource list than with the general method proposed here augmenting our language with such lists should not prove difficult. The treatment of concurrent actions in the specification languages A c (Baral Gelfond, 1997) and C (Giunchiglia Lifschitz, 1998) has many features in common with our extension of STRIPS (although C, in particular, is a very expressive language with many additional features) These languages allow the use of complex actions which are sets of primitive actions analogous to the ....

Baral, C., & Gelfond, M. (1997). Reasoning about effects of concurrent actions. Journal of Logic Programming, 85--117.

....for reasoning over updates. 9.1 Reasoning about Actions The agent needs to reason about direct and indirect effects of its actions, possibly involving several temporal units belonging to future time states. Effects may be nondeterministic, requiring the agent to take into account concurrency [23] and ramifications [82] In this field, much work has been spent on describing and discussing the features of alternative action languages [78, 107] together with the corresponding reasoning mechanisms, combining them with temporal action logics or with the situation calculus [83] A review of ....

.... with actions and planning [107, 45] Reasoning tasks involve here the evolution of the worlds, and have to face various aspects, including: the action choices available to the agent itself; their (possibly nondeterministic [82] effects; the possible results of concurrent actions [23]; uncertainties about the effective state of the world [81] events in the world not known to the agent in advance and possibly affecting its decisions. A number of action languages have been developed and discussed (cf. 78, 107] as to their expressivity and the possibility of querying ....

C. Baral and M. Gelfond. Reasoning About Effects of Concurrent Actions. Journal of Logic Programming, 31(1--3):85--117, 1997.

....as we did in the bouncing balls example, omit this constraint from the axioms when it is known from the problem description that the time variable t necessarily satisfies this constraint. 6 Discussion and Conclusions By basing it on the language A of Gelfond and Lifschitz [6] Baral and Gelfond [3] provide a semantic account of concurrency which, although not formulated in the situation calculus, has many similarities with ours. The principal difference is that Baral and Gelfond focus exclusively on concurrency, so their ontology does not include time or natural actions. Moreover, AC , ....

C. Baral and M. Gelfond. Reasoning about effects of concurrent actions. Journal of Logic Programming, 1996. to appear.

.... representation allowing partially overlapping actions and actions with different durations has been avoided, as it requires more complex temporal planning (see e.g. oplan or parcplan Currie Tate, 1991; Lever Richards, 1994) Our joint action representation has more resemblance with A C (Baral Gelfond, 1997) and C (Giunchiglia Lifschitz, 1998) where sets of actions are performed at each time step. In contrast to these approaches, though, we model multi agent domains. An important issue to address when introducing concurrent actions is synergetic effects between simultaneously executing actions ....

....and cannot be performed concurrently. The current version of NADL only avoids destructive synergetic effects. It does not include ways of representing constructive synergetic effects between simultaneous acting agents (Lingard Richards, 1998) A constructive synergetic effect is illustrated in Baral and Gelfond (1997), where an agent spills soup from a bowl when trying to lift it up with one hand, but not when lifting it up with both hands. In C and A C this kind of synergetic effects can be represented by explicitly stating the effect of a compound action. A similar approach could be used in NADL, but is ....

Baral, C., & Gelfond, M. (1997). Reasoning about effects of concurrent actions. The Journal of Logic Programming, 85--117.

....true and being caused is used here to define the syntax and semantics of a language for representing transition diagrams. We use the new language C to formalize a number of examples of reasoning about action, relate C to causal logic, and compare it with A and with the extension of A proposed by Baral and Gelfond [1997] for describing the concurrent execution of actions. In this preliminary report, discussion is limited to the propositional fragment of C, in which all fluents are truth valued, and neither fluents nor actions are allowed to have parameters. The full language is described in a forthcoming paper. ....

....have been placed. If one end of the table has been raised, a cup on the table falls off. But if both ends are lifted simultaneously, the cup remains fixed. Formalizing (a modification of) this example in the situation calculus is discussed in Section 8.3. 2 of (Gelfond, Lifschitz, Rabinov 1991) Baral and Gelfond [1997] expressed Pednault s example in their action language AC (see the next section) Turner [1996] formalized it using a static law, and our representation of this example in C is based on the same idea. We describe the positions of the two ends of the table by the fluents Up1 and Up2 . By default, ....

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Baral, C., and Gelfond, M. 1997. Reasoning about effects of concurrent actions. Journal of Logic Programming 31.

....the intuition behind this syntax will be clear. Logics like PMON will have similar problems with this construct, but for reasons of space, an example of that is omitted. 2 For an example with interactions between concurrently executed actions, see DB97 (which is the soup bowl lifting example of [ Baral and Gelfond, 1997 ] 3.2 Semantics We now define the semantics of the temporal logic. The semantics will be directly defined in terms of scenario descriptions; note however that the semantics will be identical to the standard semantics of the basic temporal logic of DB97 if we set I = Definition 7 Let oe = ....

Chitta Baral and Michael Gelfond. Reasoning about effects of concurrent actions. Journal of Logic Programming, 31:85--118, 1997.

....true and being caused is used here to define the syntax and semantics of a language for representing transition diagrams. We use the new language C to formalize a number of examples of reasoning about action, relate C to causal logic, and compare it with A and with the extension of A proposed by Baral and Gelfond [1997] for describing the concurrent execution of actions. In this preliminary report, discussion is limited to the propositional fragment of C, in which all fluents are truth valued, and neither fluents nor actions are allowed to have parameters. The full language is described in a forthcoming paper. ....

....objects have been placed. If one end of the table has been raised, a cup on the table falls off. But if both ends are lifted simultaneously, the cup remains fixed. Formalizing (a modification of) this example in the situation calculus is discussed in Section 8.3. 2 of [ Gelfond et al. 1991 ] Baral and Gelfond [1997] expressed Pednault s example in their action language AC (see Section 6.1 below) Turner [1996] formalized it using a static law, and our representation of this example in C is based on the same idea. We describe the positions of the two ends of the table by the fluents Up1 and Up2 . By ....

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Chitta Baral and Michael Gelfond. Reasoning about effects of concurrent actions. Journal of Logic Programming, 31, 1997.

....while Baker s method is based on circumscription. Kartha also showed that the soundness and completeness theorems hold for all his three translations. Kartha and Lifschitz [33] also considered how to deal with ramifications in A by using nested abnormality theory [41] Baral and Gelfond [7, 8] extended the action language A with concurrent actions and presented two translations into extended logic programs and disjunctive logic programs, respectively. Dung presented a translation of domain descriptions in A into abductive logic programs with database updates as applications [18] ....

....and terminated by these subactions will be regarded as undefined in the new situation resulting from doing the action. The above four postulates will be made clear and precise in the definition of the semantics of domain descriptions in A CO . The first postulate above is the same as that made in [24, 7, 8], among others. It is actually related to the so called common sense inertia law [24] Informally, it says that a fluent keeps unchanged after occurrence of an action if it is not changed by it. The second postulate above is also same as that assumed in [24, 7] The third postulate, called ....

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Baral, C. and Gelfond, M., Reasoning about Effects of Concurrent Actions, University of Texas at El Paso, Manuscript, 1994

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C. Baral and M. Gelfond. Reasoning about effects of concurrent actions. Journal of Logic Programming, 31(1-3):85--117, May 1997.

.... constraints by default rules with empty consequents (or false as the consequent) and in case of logic programs constraints are represented using rules with empty head (or false in the head) Baral and Gelfond also represent observations as constraints in their logic programming formulation in [BG97] and Baral, Gabaldon and Provetti in [BGP98b,BGP98a] use nested circumscription to formulate narratives. 1.2 Relating filtering and abductive reasoning: Motivations Besides the fact that both filtering and abductive reasoning are used for assimilating observations, our motivations to study the ....

....to extend the results in this paper for the more general case obtained by lifting the restriction that if an atom is abducible then so is its negation. 8 it (in Sections 4.2 and 4. 3) to show the filter abducibility of several logic programming and default theory based formulations [Tur97,BG97,MT95,MT97] of reasoning about actions. In these formulations, each model corresponds to the evolution of the real state of the world, and the abducibles correspond to the value of fluents in the initial state of the world. Thus each potential explanation needs to be a complete interpretation of ....

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C. Baral and M. Gelfond. Reasoning about effects of concurrent actions. Journal of Logic Programming, 31(1-3):85--117, May 1997.

.... in [Bro87] which were extremely useful, to general and provenly correct theories [GL93, San92, San94, Rei91, LS91, LS95] that incrementally consider various specification aspects such as: actions with non deterministic effects [Bar95, Pin94, KL94, San93] concurrent actions [LS92, BG93, BG97a] narratives [MS94, PR93, BGP97, BGPml, Kar98] actions with duration [Sho86, San89, San93, San94, MS94, Rei96] natural events [Rei96] ramifications and qualifications due to simple and causal constraints [LR94, KL94, Bar95, Lin97, Thi97, MT95, Lin95, Bar95, GL95, San96, GD96] sensing (or ....

....; a m;km ]g, we 11 We often denote this situation by [a1 ; an ]s. 12 denote a compound action, whose execution corresponds to the concurrent execution of the sequences of actions [a 1;1 ; a 1;k1 ] a m;1 ; a m;km ] Compound actions are treated in [BG93, BG97a, LS92, GLR91, ALP94] While, in [BG93, BG97a, LS92, GLR91] concurrent execution of actions are more like parallel execution, in [ALP94] concurrent execution of actions correspond to concurrent transaction processing in databases. When we refer to a plan that achieves a goal, the plan consists of ....

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C. Baral and M. Gelfond. Reasoning about effects of concurrent actions. Journal of Logic Programming, 31(1-3):85--117, May 1997.

....in the world. It is easy to see that for a domain description D in AK , the transition function Phi of D is unique. Also, notice that our definition of the transition function does not stipulate any special requirement on how the Res function is defined. Thus, any action description language [BG97, KL94, Tur97] with a semantics depending on a state transition function like Res can be extended to allow sensing actions. Thus, several of the other features of action description languages such as ramification, causality, concurrent actions, can be directly added to our framework. We do not do ....

.... domain descriptions to disjunctive logic programs Logic programming has been one of the standard logical languages that has been used in formalizing reasoning about actions [BG94, AB91] and has also been used in translating domain descriptions in high level action description languages [GL93, BG97, Bar95, Tur97, DMB92, Dun93, Sha97] Besides being a widely studied knowledge representation language with regular international conferences (for example: International conference on logic programming; International logic programming symposium, and International conference on logic programming ....

C. Baral and M. Gelfond. Reasoning about effects of concurrent actions. Journal of Logic Programming, 31(1-3):85--117, May 1997.

.... [HM87] also, papers in [Bro87] which were extremely useful, to general and provenly correct theories [GL93,San92,Rei91,LS91,LS95] that incrementally consider various specification aspects such as: actions with non deterministic effects [Bar95,Pin94,KL94] concurrent actions [LS92,BG93,BG97] narratives [MS94,PR93,BGP97,BGP96] actions with duration [MS94,Rei96] natural events [Rei96] ramifications and qualifications due to simple and causal constraints [LR94,KL94,Bar95,Lin97,Thi97,MT95] Lin95,Bar95,GL95] sensing (or knowledge producing) actions ....

.... For example, by f[a 1;1 ; a 1;k 1 ] a m;1 ; a m;km ]g, we denote a compound action, whose execution corresponds to the concurrent execution of the sequences of actions [a 1;1 ; a 1;k 1 ] a m;1 ; a m;km ] Compound actions are treated in [BG93,BG97,LS92,GLR91,ALP94] While, in [BG93,BG97,LS92,GLR91] concurrent execution of actions are more like parallel execution, in [ALP94] concurrent execution of actions correspond to concurrent transaction processing in databases. When we refer to a plan that achieves a goal, the plan consists of only ....

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C. Baral and M. Gelfond. Reasoning about effects of concurrent actions. Journal of Logic Programming, 31(1-3):85--117, May 1997. 46

....physical objects of the world that may change their values, or mental objects that encode the mental state of the robot agent. For example, loaded is fluent which tells us if the gun is loaded or not. 4 actions with non deterministic effects [Bar95,Pin94,KL94] concurrent actions [LS92,BG93,BG97a] narratives [MS94,PR93,BGP97,BGP96] actions with duration [MS94,Rei96] natural events [Rei96] ramifications and qualifications due to simple and causal constraints [LR94,KL94,Bar95,Lin97,Thi97,MT95] Lin95,Bar95,GL95] sensing (or knowledge producing) actions [SL93,JTM97] etc. Most of the ....

.... For example, by f[a 1;1 ; a 1;k 1 ] a m;1 ; a m;km ]g, we denote a compound action, whose execution corresponds to the concurrent execution of the sequences of actions [a 1;1 ; a 1;k 1 ] a m;1 ; a m;km ] Compound actions are treated in [BG93,BG97a,LS92,GLR91,ALP94] While, in [BG93,BG97a,LS92,GLR91] concurrent execution of actions are more like parallel execution, in [ALP94] concurrent execution of actions correspond to concurrent transaction processing in databases. When we refer to a plan that achieves a goal the plan consists of only ....

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C. Baral and M. Gelfond. Reasoning about effects of concurrent actions. Journal of Logic Programming, 31(1-3):85--117, May 1997.

....filtering makes intuitive sense In this paper we try to provide some answer to this question and give conditions on theories when filtering corresponds to abductive reasoning. Finally, since [San89] filtering in some form or other has been used in many action formalizations. Baral and Gelfond [BG97] and Turner [Tur95,Tur97] use logic program rules with empty head (or false in the head) to represent observations as filters to a theory of action expressed using logic programs. Turner also uses default rules with empty consequents (or false as the consequent) to represent observations as ....

....to T . Otherwise, i.e. if T is in a non monotonic language we can not just add Q to T . If T is a logic program to filter T by Q we can view Q as an integrity constraint. Often integrity constraints are expressed through rules with empty head or with false in its head. Such a view is used in [Tur97,BG97] to assimilate observations to action theories expressed in a logic program. In [Llo87] an algorithm is given to translate general formulas to the restricted syntax of integrity constraints in logic programs. If T is a default theory to filter T by Q we can express Q as a default rule with an ....

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C. Baral and M. Gelfond. Reasoning about effects of concurrent actions. Journal of Logic Programming, 31(1-3):85--117, May 1997.

....of the various basic relations, and the views, together with an interpretation of some additional propositional constants that are used to record the occurrence of external actions. We refer to these additional propositional constants as external fluents, the term used in reasoning about actions [2, 3]. A database state is said to be in a consistent state if it satisfies all the integrity constraints. Before we present the semantics we first introduce some notations. ffl Unfold(S,DB) Unfold(S, DB, New Old) The unfolding of an SQL modification statement S w.r.t. DB gives us a triplet (called ....

....schema with new relation schemes with same name as the functions and with attribute names corresponding to the formal input parameters of the functions. The type of the attributes is the type of the parameters. The effect of user defined actions are represented as effect axioms (in the style of [16, 2, 3]) of the following form: a causes f if p where, a is the external action, f is a fluent whose value is changed by a and p is an SQL query w.r.t. the database. Intuitively, the axiom means that after the execution of a, in a data base state where p is true, f becomes true. For example, the ....

C. Baral and M. Gelfond. Reasoning about effects of concurrent actions. Journal of Logic Programming, 31(1-3):85--117, May 1997.

....a database description and queries about the state of the database after the execution of a sequence of transactions. Because of its commonality with the recent works on action description languages our language can be easily extended to incorporate additional features such as concurrent actions [BG96] and deductive rules [KL94, Bar95, LR94] We start with a presentation of the syntax and semantics of the language. We then present a translation that takes an active database description into a logic program. This translation provides us a vehicle to actually compute the entailment relation. We ....

.... allow concurrent and complex actions where a complex action is defined in terms of simple actions, allow temporal conditions, and compare the use of temporal conditions vs. complex events. We have some ideas of how to do this based on previous work on concurrent and complex actions [BG96, LLL 94, BK93] and temporal conditions [MLLB96, SW95] In general, we believe that the methodology of using a transition system or automata is a promising approach to formally describe the semantics of active databases. ....

C. Baral and M. Gelfond. Reasoning about effects of concurrent actions. Journal of Logic Programming (to appear), 1996.

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Baral C, Gelfond M. Reasoning about effects of concurrent actions. Journal of Logic Programming 1997; 31:85-118.

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C. Baral and M. Gelfond. Reasoning about effects of concurrent actions. J. Logic Program., 31:85--117, 1997.

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