Re: Annotations, sets, & servers

  >But what about the other way around?  Can one annotation set be
  >broken across multiple servers?  For really large annotation sets
  >(billions of entries), it might be desirable to split up the
  >load across many machines; indeed, I can envision some annotation
  >sets that are geographically dispersed around the world.  (It turns
  >out that the architecture of my prototype annotation proxy supported
  >cross machine annotation sets.)
  >For example, I might have 26 machines allocated such that they
  >served up annotations based on the first letter organziation name.
  >Thus, the annotations for objects on http://www.W3.org/... would
  >go to machine W (for W3) and the annotations for http://www.Sun.com/
  >would go to machine S (for Sun).

Fine. But I would claim that this is the wrong level to think about
these kinds of issues.  Every annotation server has a database backend
which basically stores the annotations for each set. (How this is done
is not part of our job here now.)  You can easily realize your above
example by simply picking a distributed database for this backend in a
specific case (or, as mentioned before, use a shared file server
realization). No problem. The question is whether to move all these
issues up one conceptual level and consider the concept of a set to be
distributed.  And here I argued that the additional complexity in
terms of access control etc. does not warrant this extra step,
especially since it isn't a good idea anyway to mix up conceptually
distinct issues.

Another way to put this is that annotation hot spots will happen, but
solutions to it are orthogonal to the protocol. There should be a
general solution to this problem, and the same solutions which are
used for document hot spots should then be applied towards annotation
hot spots. (And, as you pointed out before, the basic constraint is
that architecture should not make things worse than they are.)

  >For me, an annotation is an ordered pair (i.e. relation) of
  >target documents and annotation documents.  In the simplest case,
  >there is a single target document and a single annotation document:
  >	({target_url}, {annotation_url})

Exactly, in other words the annotation schema does not assert any
functional dependency between annotated URL and annotation URL.

Cheers, - Martin


- M