As you may know, BibSonomy supports the use of relations between tags. Thus, you can structure your tags, e.g. by stating that every resource tagged with "java" should also be considered to be related to "programming". To do this, you'd tag one resource with "java->programming" or insert that relation explicitly on the "edit tags" page.
There's one more way to insert relations: say you're looking at your "java" page and you think, gee, this is all "programming" stuff. So you decide to tag your own "java" page with "programming".
If you do that, you're inserting a relation between "java" and "programming" into your part of BibSonomy. Notice the drop down box under the tag line in the posting dialog. There you can choose which direction the relation should be: "java->programming" (everything "java" is also about "programming"), or the other way around (which doesn't make sense in this example).
This works for global tag pages such as http://www.bibsonomy.org/tag/java as well for your own tag pages, e.g. http://www.bibsonomy.org/user/schmitz/java.
Remember, you can make use of relations not only to structure your content, but also to find all resources e.g. tagged with "java", even when querying the tag "programming" as a concept.
Happy tagging,
Christoph