Over time, of course, all file systems have evolved in the direction of richer metadata. The star-crossed BeOS left one important signpost. The Be File System supported unlimited amounts and types of file metadata and could effectively index and query that metadata years before its spiritual descendant, Apple's Spotlight, arrived on the scene.
Another signpost is ReiserFS, a journaling file system that's used in a number of Linux distributions. In Version 4, which was recently released, speed, reliability, and extensibility were all priorities, but the long-term goal is to model information in ways that are friendlier to the associative style of human thought. "We very much share the BeFS vision of enhancing the file system namespace semantics," architect Hans Reiser has said. To get there, it was first necessary to create a flexible, high-performance foundation for managing metadata. Now that's done, he says, and the next phase -- "adding search engine and database semantic features into the file system namespace" -- can begin.
Bringing it all together
As we weave more and better metadata into software, documents, Web sites, and file systems, the information stored in these various containers will become more available, more cohesive, and therefore more useful. The next challenge is how -- in this new era of interconnected systems, people, and business processes -- to unite these separate realms.
The solution is a complex recipe, but we can find many of the ingredients at work in the emerging discipline of SOA (service-oriented architecture). We use metadata to describe the interfaces to services and to define the policies that govern them. The messages exchanged among services carry metadata that interacts with those policies to enable dynamic behavior and that defines the contexts in which business transactions occur. The documents that are contained in those messages and that represent those transactions will themselves also be described by metadata.
There's no overarching schema for the metadata that flows through the service network, touching routers, registries, security gateways, databases, and end-user applications. And, in view of its many forms and uses, it's not clear that convergence on a single standard is necessary or even desirable. What is necessary is that within each metadata domain we strike healthy balances between the constraints we apply to metadata vocabularies and the evolutionary freedom we allow them. Across domains, we'll speak the lingua franca of data and metadata, namely XML.