> Now, assume I have a generic tag programming, and a couple of more specific tags: python and c. I definitely want my bookmarking service to be smart enough to figure that if I tag some article with either python or c, it means programming as well; I don't want to add the tag programming manually every single time. So, what we need is a hierarchy of tags. Surprisingly enough, I failed to find a service which would support that.
What about Pinboard's tag bundles?