Service composition is a major advance service-oriented computing brings to enable the development of distributed applications. However, the distributed nature of services hampers their composition with data heterogeneity problems. In this paper, we address these problems with a decentralised mediation-as-a-service architecture that solves data inconsistencies occurring during the composition of business services. As an extension to our previous work that focused on data interpretation problems, we present in this paper a solution to solve data inconsistencies at the syntactic, structural and semantic levels. We show how syntactic, structural and semantic mediation techniques can be combined, and how semantic mediation provides useful information that helps structural and syntactic mediation. We demonstrate how our architecture enables decentralised publication and discovery of mediation services. We motivate our work with a concrete scenario and validate our proposal with experiments.