After my previous entry on Translations, Glosses, Tags and Folksonomies, I started thinking about some of the other limitations with tags as well, including normalising synonyms and expressing hierarchy or grouping.
One solution could solve both. If you could have a tag that meant the union of certain other tags, you could create a parent tag for all the synonyms. Taxonomists might shudder at the conflation of synonymity with grouping but it seems entirely appropriate for a folksonomy.
Of course, any tag should be allowed to have multiple parents where it fits into multiple larger categories (noting that parents generalise, not specialise)
How might these grouping be expressed? Well it just dawned on me:
Tag the Tags
If tags themselves could be tagged, a much richer taxonomy could be built. You could have tag groupings, tag types, etc. And none of it would interfere with the existing data.
Of course, it's poor-man's RDF with only one property and tags instead of URIs, but, hey, it just might work for folksonomies.