XACML is an Oasis standard that is starting to gain popularity for controlling access to digital resources. There are several implementations but the most popular is Sun's XACML interpreter.
I've submitted a paper for this spring's AFCEA conference that describes a full XACML compiler that we expect to release as government open source on forge.mil soon. Although I developed it to make XACML more readable and amenable to easy debugging, not speed, the early non-optimized version is blazingly fast, far faster than the Sun interpreter.
The draft is available here. This was written before I started work on the Oasis Conformance Tests. That has now been completed and I'm updating the draft to describe the new version. I'll post it here when ready.
Note Added 18 Mar 2011: The updated paper has been published to the link shown above.