An advanced e-Science middleware system is designed and implemented to support search and retrieval of scientific information. It is capable of integrating collections of scientific datasets, including simulation models and associated tools for statistical analysis and dataset visualization. These collections represent application software in several scientific domains, they reside in geographically disperse organizations and constitute the system content. It also actively supports on-demand scientific data processing workflows. The system design makes use of two recently advancing technologies, the Semantic Web and the Grid, as well as state of the art distributed system’s technology. The system’s demonstration scenarios involve mainly environmental applications.