Structural Subsumption for ALN

Aus der Einleitung: „In this paper, we reuse the representation formalism `description graph' in order to characterize subsumption of ALN-concepts. The description logic ALN allows for conjunction, valuerestrictions, number restrictions, and primitive negation. Since Classic allows for more constructors than ALN, e.g., equality restrictions an attribute chains by the constructor SAME-AS,we can confine the notion of description graphs from [BP94]. On the other hand, ALN explicitly allows for primitive negation which yields another possibility { besides conflicting number restrictions { to express inconsistency. Thus, we have to modify the notion of canonical description graphs in order to cope with inconsistent concepts in the structural characterization of subsumption. It turns out that the description graphs obtained from ALN-concepts are in fact trees. A canonical graph is a deterministic tree. The conditions required by the structural characterization of subsumption on these trees can be tested by an eficient algorithm, i.e., we obtain an algorithm deciding subsumption of C and D in time polynomial in the size of C and D. The report is structured as follows. In the preliminaries, we define syntax and semantics of the description logic ALN as well as the inference problem of subsumption. In Section 3, we introduce description graphs, the data structure our structural subsumption algorithm is working on. Besides syntax and semantics also an algorithm for translating ALN-concepts into description graphs is given. Thereafter, we present the main result of this report in Section 6, a characterization of subsumption of ALN-concepts by a structural comparison of corresponding description graphs. Furthermore, a structural subsumption algorithm can be found in Section 6.2. In the last section we summarize our results and give an outlook to further applications of structural subsumption in terminological knowledge representation systems

Planning from second principles : a logic-based approach

In this paper, a logical formalization of planning from second principles is proposed, which relies on a systematic decomposition of the planning process. Deductive inference processes with clearly defined semantics formalize planning from second principles. Plan modification is based on a deductive approach which yields provably correct modified plans. Reusable plans are retrieved from a dynamically created plan library using terminological logic as a query language to the library. Apart from sequential plans, this approach enables a planner to efficiently reuse and modify plans containing control structures like conditionals and iterations

A Complete Subsumption Algorithm

Efficiency of the first-oC er loCA pro o procedure is a majo r issue when deductio n systems areto be used in real enviro nments, bo th o theiro wn and as aco p o ento f larger systems (e.g., learning systems). Hence, the needo techniques that can perfo; such a pro cess with reduced time/space requirements (specifically when perfo rming reso3 tio ). This paper pr ooA: a newalgo66 hm that is able to return the wh o# set osoA tio s to #-subsumptio pro blems by co mpactly representing substitutio ns. It co uld be explo ited when techniques available in the literature areno t suitable. Experimental resultso n its performance are encouraging

A complete Subsumption Algorithm

Efficiency of the first-order logic proof procedure is a major issue when deduction systems are to be used in real environments, both on their own and as a component of larger systems (e.g., learning systems). Hence, the need of techniques that can perform such a process with reduced time/space requirements (specifically when performing resolution). This paper proposes a new algorithm that is able to return the whole set of solutions to theta-subsumption problems by compactly representing substitutions. It could be exploited when techniques available in the literature are not suitable. Experimental results on its performance are encouraging