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 decentralized Mediation-as-a-Service architecture that solves data inconsistencies occurring during the composition of business services. As a particular data heterogeneity, we focus on the data interpretation problem and introduce conflictual aspect mediation services and conflictual aspect ontologies to solve data interpretation inconsistencies. We demonstrate how our architecture enables decentralized publication and discovery of mediation services. We motivate our work with a concrete scenario and validate our proposal with experiments.