High-performance computing faces considerable change as the Internet and the Grid mature. Applications that once were tightly-coupled and monolithic are now decentralized, with collaborating components spread across diverse computational elements. Such distributed systems most commonly communicate through the exchange of structured data. Definition and translation of metadata is incorporated in all systems that exchange structured data. We observe that the manipulation of this metadata can be decomposed into three separate steps: discovery, binding of program objects to the metadata, and marshaling of data to and from wire formats. We have designed a method of representing message formats in XML, using datatypes available in the XML Schema specification. We have implemented a tool, XMIT, that uses such metadata and exploits this decomposition in order to provide flexible run-time metadata definition facilities for an efficient binary communication mechanism. We also demonstrate that the use of XMIT makes possible such flexibility at little performance cost.

It is our belief that network applications relying on globally distributed shared resources will increasingly adopt meta-level descriptions to describe the data streaming in the application at runtime. Our group has developed the notion of computational data streams to describe and act upon such data flows. Our work conceptualizes the data flows as database relations over which useful operations, such as querying, can be performed. This paper shows how one can make the step from a meta-level description of data flows to an actual implementation using CORBA-style event channels and binary I/O for data transport.

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