We investigate the computational capabilities of Web browsers, when equipped with a standard finite automaton. We observe that Web browsers are Turing-complete. We introduce the notion of a navigational problem, and investigate the complexity of solving Web queries and navigational problems by Web browsers, where complexity is measured by the number of clicks.

We introduce and investigate a distributed computation model for querying the Web. Web queries are computed by interacting automata running at different nodes in the Web. The automata which we are concerned with can be viewed as register automata equipped with an additional communication component. We identify conditions necessary and sufficient for systems of automata to compute Web queries, and investigate the computational power of such systems.

Motivated by recent work of Abiteboul, Vianu, Fordham, and Yesha [3] we investigate the verifiability of transaction protocols specifying the interaction of multiple partiesvia a network, where each party is equipped with an (active) database that participates in the interaction. Such transaction protocols typically occur in the context of electronic commerce applications and can be formalized as relational transducers. We introduce a class of powerful relational transducers based on Gurevich's abstract state machines and show that several verification problems related to electronic commerce applications can be solved for these transducers. Our approach is, in some sense, complementary to the approach in [3].