Discussiones Mathematicae Graph Theory 27(3) (2007) 565-582
doi: 10.7151/dmgt.1383

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Stanisław Bylka  and  Jan Komar

Institute of Computer Science
Polish Academy of Sciences
21 Ordona street, 01-237 Warsaw, Poland
e-mail: bylka@ipipan.waw.pl
e-mail: komjan@operamail.com


This paper deals with weighted set systems (V,E,q), where V is a set of indices, E ⊂ 2V and the weight q is a nonnegative integer function on E. The basic idea of the paper is to apply weighted set systems to formulate restrictions on intersections. It is of interest to know whether a weighted set system can be represented by set intersections. An intersection representation of (V,E,q) is defined to be an indexed family R = (Rv)v ∈ V of subsets of a set S such that

v ∈ E 
= q(E)   for eachE ∈ E.

A necessary condition for the existence of such representation is the monotonicity of q on E i.e., if F ⊂ E then q(F) ≥ q(E). Some sufficient conditions for weighted set systems representable by set intersections are given. Appropriate existence theorems are proved by construction of the solutions.

The notion of intersection multigraphs to intersection multi- hypergraphs - hypergraphs with multiple edges, is generalized. Some conditions for intersection multi-hypergraphs are formulated.

Keywords: intersection graph, intersection hypergraph.

2000 Mathematics Subject Classification: 05C62, 05C65.


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Received 13 February 2006
Revised 24 October 2007
Accepted 24 October 2007