Grid technology provides a suitable platform for resource sharing, offering users the possibility of accessing large-scale controlled environments across different organizational boundaries through a virtualized single environment. In order to control accesses to those resources, a unique and global security infrastructure is needed, such as a PKI and Virtual Organizations. Hence, in order to process data in the grid, it must be first uploaded to a suitable resource belonging to the grid. We propose mechanisms to extend the grid data space boundaries by securely integrating data located in the client local file system or in external repositories. The proposed extensions only take place during execution of an application on the grid, preserving privacy and other security properties. We explain their implementation in SUMA/G, a middleware built on top of Globus, and show some experiment results.