Browsing by Author "Gaspar, G."
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- Computing Repairs from Active Integrity ConstraintsPublication . Cruz-Filipe, L.; Engrácia, P.; Nunes, I.; Gaspar, G.Repairing an inconsistent knowledge base is a well known problem for which several solutions have been proposed and implemented in the past. In this paper, we start by looking at databases with active integrity constraints - consistency requirements that also indicate how the database should be updated when they are not met - as introduced by Caroprese et al.We show that the different kinds of repairs considered by those authors can be effectively computed by searching for leaves of specific kinds of trees. Although these computations are in general not very efficient (deciding the existence of a repair for a given database with active integrity constraints is NP-complete), on average the algorithms we present make significant reductions on the number of nodes in the search tree. Finally, these algorithms also give an operational characterization of different kinds of repairs that can be used when we extend the concept of active integrity constraints to the more general setting of knowledge bases.
- Patterns for Interfacing between Logic Programs and Multiple OntologiesPublication . Cruz‐Filipe, L.; Nunes, I.; Gaspar, G.Originally proposed in the mid-90s, design patterns for software development played a key role in object-oriented programming not only in increasing software quality, but also by giving a better understanding of the power and limitations of this paradigm. Since then, several authors have endorsed a similar task for other programming paradigms, in the hope of achieving similar benefits. In this paper we discuss design patterns for hybrid semantic web systems combining several description logic knowledge bases via a logic program. We introduce eight design patterns, grouped in three categories: three elementary patterns, which are the basic building blocks; four derived patterns, built from these; and a more complex pattern, the study of which can shed some insight in future syntactic developments of the underlying framework. These patterns are extensively applied in a natural way in a large-scale example that illustrates how their usage greatly simplifies some programming tasks, at the level of both development and extension. We work in a generalization of dl-programs that supports several (possibly different) description logics, but the results presented are easily adaptable to other existing frameworks such as multi-context systems.
- Tighter integration in dl-programsPublication . Cruz-Filipe, L.; Engrácia, P.; Gaspar, G.; Henriques, R.; Nunes, I.; Santos, D.We introduce a mechanism called lifting to share predicates between the two components of a dl-program, integrating them in a tighter way. Using lifting, one can reason about the predicates being shared both via the description logic knowledge base and via Datalogstyle rules, and the deductions one makes are automatically reflected globally on both components. This is a capability not directly present in dl-programs, since changes to the knowledge base only affect the queries where they occur. We show that lifting has nice theoretical properties, making it suitable for modular design of dl-programs. Furthermore, dlprogram processors can easily incorporate lifting as a new operator, and we have extended dlvhex to work with dl-programs with lifting.