Disjunctive Logic Programming (DLP) is a very expressive formalism: it allows for expressing every property of finite structures that is decidable in the complexity class Σ P 2 (=NP NP ). Despite this high expressiveness, there are some simple properties, often arising in real-world applications, which cannot be encoded in a simple and natural manner. Especially properties that require the use of arithmetic operators (like sum, times, or count) on a set or multiset of elements, which satisfy some conditions, cannot be naturally expressed in classic DLP.To overcome this deficiency, we extend DLP by aggregate functions in a conservative way. In particular, we avoid the introduction of constructs with disputed semantics, by requiring aggregates to be stratified. We formally define the semantics of the extended language (called DLP A ), and illustrate how it can be profitably used for representing knowledge. Furthermore, we analyze the computational complexity of DLP A , showing that the addition of aggregates does not bring a higher cost in that respect. Finally, we provide an implementation of DLP A in DLV-a state-of-the-art DLP system -and report on experiments which confirm the usefulness of the proposed extension also for the efficiency of computation. A preliminary version of this work appeared in the Proceedings of IJCAI-03.1. if p occurs in B + (r) and p ′ occurs in H(r), then ||p|| n ≤ ||p ′ || n ; and 2. if p occurs in B − (r) and p ′ occurs in H(r), then ||p|| n < ||p ′ || n ; and 3. if p and p ′ occur in H(r), then ||p|| n = ||p ′ || n . Aggregate-stratification.The idea of aggregate-stratification is that two predicates defined by means of aggregates do not mutually depend on one another.A DLP A program P is aggregate-stratified if there exists a level mapping || || a such that for each pair p and p ′ of predicates of P, and for each rule r ∈ P,

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Remaining in business and growing is a challenge for small and medium-sized enterprises (SMEs) in the food sector. The focus of this paper is the internal innovation avenue for SMEs that have been trading for decades and have developed the asset of enterprise cultural heritage (ECH). The authors examine ECH as a source of sustainable competitive advantage, using the value, rarity, imitability and organization (VRIO) framework and evaluating the practical potential of ECH to create sustainable competitive advantage through case studies of two international companies. The authors argue that companies that are only partially able to fulfil each of the VRIO criteria can still claim sustainable competitive advantage, as demonstrated by the case studies. Moreover, it is suggested that ECH is one of the key areas for innovation from within a firm and should be used in developing sustainable competitive advantage.

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