Descriptive Complexity Theory
Part of the Perspectives in Mathematical Logic book series (PML)
In Chapter 0 we gave the example of a database D that contains the names of the main cities in the world and the pairs (a, b) of cities such that a given airline offers service from a to b without stopover. D may be interpreted as a first-order structure, more precisely, as a digraph G = (G,E G ), where G is the set of cities and E G ab means that there is a flight from a to b without stopover. Now, first-order logic may be viewed as a query language. For example, let
$$ \varphi (x,y): = Exy \vee \exists z(Exz \wedge Ezy) $$
KeywordsVerse Imid Prool
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© Springer-Verlag Berlin Heidelberg 1995