  A critical component in the implementation of an efficient tabling system is
the design of the table space. The most popular and successful data structure
for representing tables is based on a two-level trie data structure, where one
trie level stores the tabled subgoal calls and the other stores the computed
answers. The Global Trie (GT) is an alternative table space organization
designed with the intent to reduce the tables's memory usage, namely by storing
terms in a global trie, thus preventing repeated representations of the same
term in different trie data structures. In this paper, we propose an extension
to the GT organization, named Global Trie for Subterms (GT-ST), where compound
subterms in term arguments are represented as unique entries in the GT.
Experiments results using the YapTab tabling system show that GT-ST support has
potential to achieve significant reductions on memory usage, for programs with
increasing compound subterms in term arguments, without compromising the
execution time for other programs.
