2005 European Conference on Combinatorics, Graph Theory and Applications (EuroComb '05)
Stefan Felsner (ed.)
DMTCS Conference Volume AE (2005), pp. 293298
author:  Gyula O.H. Katona and Krisztián Tichler 

title:  An extremal problem on trees and database theory 
keywords:  labelled directed tree, relational database, minimum matrix representation, extremal problems 
abstract: 
We consider an extremal problem on labelled directed trees
and applications to database theory. Among others, we will
show explicit keysystems on an underlying set of size
n
, that cannot be represented by a database of less
than
2
rows.
n(1c·
log
log
n/
log
n)

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reference:  Gyula O.H. Katona and Krisztián Tichler (2005), An extremal problem on trees and database theory, in 2005 European Conference on Combinatorics, Graph Theory and Applications (EuroComb '05), Stefan Felsner (ed.), Discrete Mathematics and Theoretical Computer Science Proceedings AE, pp. 293298 
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