This thesis reports on the results of a study of the nested join operator in a mediator-based setting. As the rate at which data is accumulated increases, the need for integration of di erent (physical) Database Management Systems (DBMS) becomes apparent. The most fundamental and arguably important operation that is used in order to achieve this is the join-operator. The nested-relational model...

We show that every generalized high Turing degree is the join of two minimal degrees, thereby settling a conjecture of Posner’s from the 70s.

Considering a commutative unital quantale L as the truth value table and using the tool of L-generalized convergence structures of stratified L-filters, this paper introduces a kind of fuzzy upper topology, called fuzzy S-upper topology, on L-preordered sets. It is shown that every fuzzy join-preserving L-subset is open in this topology. When L is a complete Heyting algebra, for every completel...

Bernstein and Goodman showed that natural inequality ( NI) queries can be processed efficiently by semijoins, if there are no multiple inequality join edges, nor cycles with one or zero doublet. In this paper procedures to hand1 e these cases efficiently are given. Multiple inequality join edges can be processed by multi-attribute inequality semijoins. Two procedures based on generalized semi-j...

The paper presents an iterative version of join-tree clustering that applies the message passing of join-tree clustering algorithm to join-graphs rather than to join-trees, iteratively. It is inspired by the success of Pearl’s belief propagation algorithm (BP) as an iterative approximation scheme on one hand, and by a recently introduced mini-clustering (MC(i)) success as an anytime approximati...

A generalized vertex join of a graph is obtained by joining an arbitrary multiset of its vertices to a new vertex. We present a low-order polynomial time algorithm for finding the chromatic polynomials of generalized vertex joins of trees, and by duality we find the flow polynomials of arbitrary outerplanar graphs. We also present closed formulas for the chromatic and flow polynomials of vertex...