It's middleware for metadata:

• Transparent access to distributed resources
• Data discovery and query optimization
• Distributed processing and virtual archives

It's a software architecture:

• Models for information representation
• Solutions to knowledge capture problems
• Unification of technology, data, and metadata

How does it work?

• An example of what it does
• Our classic paper (and a good conceptual intro, too)

Who's using it?

• National Institutes of Health
• NASA Planetary Data System
• NASA SeaWinds Earth Science Mission
• NASA QuikSCAT Earth Science Mission
• Dozens of institutions
• Space, planetary, biomedical, and other domains