The overall goal of the Stanford Digital Library project is to provide 
an infrastructure that affords interoperability among heterogeneous, 
autonomous digital library services.  These services include both search 
services and remotely usable information processing facilities. 
In this paper, we survey and categorize the metadata required for a 
diverse set of Stanford Digital Library services that we have built. 
We then propose an extensible metadata architecture that meets these 
requirements.

Our metadata architecture fits into our established infrastructure 
and promotes interoperability among existing and de-facto metadata 
standards.  Several pieces of this architecture are implemented; 
others are under construction.  The architecture includes attribute 
model proxies, attribute model translation services, metadata information
facilities for search services, and local metadata repositories.  
In presenting and discussing the pieces of the architecture, we show 
how they address our motivating requirements. Together, these components
provide, exchange, and describe metadata for information objects and 
metadata for information services.  We also consider how our 
architecture relates to prior, relevant work on these two types of metadata.