In this paper, we present an integrated system architecture for metacomputing on top of distributed scientific resources via semantic-driven information management. Our approach is to consider both data and programs as objects of an application-specific ontology, describing them via corresponding metadata schemata that can be exploited to search for and to generate information in an efficient and automated way. Metacomputations are expressed in the form of workflows thereby enabling a flexible combination of data and program objects that can reside on different servers or grid resources. Workflow descriptions are associated with ontology concepts and can be activated as a side-effect of searching for information to produce new data on demand. We also report on the current status of an implementation that provides support for several aspects of this architecture.