  Current approaches for the discovery, specification, and provision of
services ignore the relationship between the service contract and the
conditions in which the service can guarantee its contract. Moreover, they do
not use formal methods for specifying services, contracts, and compositions.
Without a formal basis it is not possible to justify through formal
verification the correctness conditions for service compositions and the
satisfaction of contractual obligations in service provisions. We remedy this
situation in this paper. We present a formal definition of services with
context-dependent contracts. We define a composition theory of services with
context-dependent contracts taking into consideration functional,
nonfunctional, legal and contextual information. Finally, we present a formal
verification approach that transforms the formal specification of service
composition into extended timed automata that can be verified using the model
checking tool UPPAAL.
