Tagging with external database identifiers

How should we indicate that a tag represents an entry in an external database?

Please see:


and comment at:


Not all external references will have an url pattern.
One key I documented that is like this: http://wiki.openstreetmap.org/wiki/Key:IBGE:GEOCODIGO
It references an external database, and doesn’t have an “official” URL for the codes.

Perhaps we should create a wiki page called “External references” to group these tags.

Technical Note: A category would be a lot more apropriate. Actually there are already at least two of them: Category:Key descriptions for group “references” and External reference tag

I went with the category External reference tag, because it’s more flexible and is already in use.

Oh, and about the main topic of this thread:
I still think the parameters ‘url_pattern’, ‘website’ and similars should be moved to another template instead of Key/ValueDescription.