Temporal validitity of subject indicators?

Hi folks,

Quick question arising from something I'm doing at the moment:  how do you invalidate/deprecate a subject indicator reference within a Topic Map ecosystem?

The issue here is that the URL used for a subject indicator can be updated over time to actually refer to a totally different subject--completely at the discretion of the owner.

What's the normal way to deal with this sort of thing?

Thanks in advance,

ast
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Andrew S. Townley <[email protected]>
http://atownley.org