Christos Nomikos

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We address the problem of maximizing the number of satisfied requests in all-optical networks that use wavelength division multiplexing. We consider the case where requests are pre-routed and formulate it as the maximum path coloring problem. We study the problem for rings and present a (2/3)-approximation algorithm. Along the way we develop a fast matching(More)
In all-optical networks that use WDM technology it is often the case that several communication requests have to be blocked, due to bandwidth and technology limitations. Minimizing request blocking is therefore an important task calling for algorithmic techniques for efficient routing and wavelength assignment. Here we study the problem for rings under both(More)
We examine the notion of bisimulation and its ramifications, in the context of the family of Heyting-valued modal languages introduced by M. Fitting. Each modal language in this family is built on an underlying space of truth values, a Heyting algebra H. All the truth values are directly represented in the language, which is interpreted on relational frames(More)
Article history: Received 29 June 2007 Revised 16 February 2008 Available online 7 June 2008 We introduce locally stratified Boolean grammars, a natural subclass of Boolean grammars with many desirable properties. Informally, if a grammar is locally stratified then the set of all pairs of the form (nonterminal, string) of the grammar can be mapped to a(More)
Motivated by the increasing importance of multifiber WDM networks we study a routing and wavelength assignment problem in such networks. In this problem the number of wavelengths per fiber is given and the goal is to minimize the cost of fiber links that need to be reserved in order to satisfy a set of communication requests; we introduce a generalized(More)
We consider the problem of extending temporal deductive databases with stratified negation. We argue that the classical stratification test for deductive databases is too restrictive when one shifts attention to the temporal case. Moreover, as we demonstrate, the (more general) local stratification approach is impractical: detecting whether a temporal(More)
Motivated by the increasing importance of multifiber WDM networks we study two routing and wavelength assignment problems in such networks: – Fiber Cost Minimization: the number of wavelengths per fiber is given and we want to minimize the cost of fiber links that need to be reserved in order to satisfy a set of communication requests; we introduce a(More)