Feature of the week: Retrieve resources by disjunction of tags

A very common way to browse through your own or other people's repository on BibSonomy is via one or more tags, e.g.

http://www.bibsonomy.org/tag/semantic+web.

Hereby, the tag-based retrieval is done in a conjunctive manner, i.e., the result of this query will comprise all bookmarks and publications tagged with semantic AND web. We are often asked if we offer any other possibiliby of combined tag queries, e.g. by disjunction - one might e.g. be interested in all resources tagged with semanticweb OR ontologies.

This behaviour is not accessible via a specific URL scheme, but can be achieved by invoking an old BibSonomy buddy - namely concepts! As you will know, BibSonomy allows you to define relations between tags in the form:

SUPERTAG <- SUBTAG

(see also http://www.bibsonomy.org/relations). A supertag along with all its subtags is denoted a concept in BibSonomy, which can be used to retrieve resources like this:

http://www.bibsonomy.org/concept/tag/ontology

The characteristics of this retrieval method is now that all resources are returned which are tagged with ontology OR one of its subtags. This constitutes, in fact, a retrieval of resources by a disjunction of tags. We are aware that this has some limitations, as a concept has to be defined before this type of query is possible - but facing a tradeoff between efficient query processing and freedom of query formulation has led us to this decision, with the ultimate goal to keep our service highly responsive for all of you as our users.