[stellation-res] Adding artifact priority

[Dave Shields <shields@xxxxxxxxxxxxxx>]

During our weekly tea at Research today, Mark mentioned an idea he has of associating
a "priority" with an artifact type, which could be used to determine the order in which
artifacts are processed. This may well offer a chance to put more function in the artifact
agents and so require less artifact-specific information in the workspace code. For example,
I am currently doing a major rewrite of the workspace, and have found several cases where
special code is needed to handle "Link" artifacts, when a more general approach should be possible.

There is (now) lots of code to see if an artifact is a Compound, to detect a directory, and so guide
a recursive traversal over the artifact set. If we had priorities, we should be able to move some
of this function into the agents.

The problem with assuming that a Compound is a directory is that when we add fine-grain artifacts, 
we will most likely need a compound to collect together fine-grain artifacts, and not just to 
represent a directory.

All this is new (and untested). However, since Mark is revising some of the artifact representation
in the database, I suggest we add a "priority" column for artifacts (or perhaps just for artifact agent),
so we can actually try to test some of these ideas.

All that really matters for an initial test is that Compound representing a directory
(as all Compounds currently do) have a distinguished priority.  I would suggest default priority of 0, with
Compound having priority 1. 

dave

-- 
Dave Shields, IBM Research, shields@xxxxxxxxxxxxxx.