  Tagging facilitates information retrieval in social media and other online
communities by allowing users to organize and describe online content.
Researchers found that the efficiency of tagging systems steadily decreases
over time, because tags become less precise in identifying specific documents,
i.e., they lose their descriptiveness. However, previous works did not answer
how or even whether community managers can improve the efficiency of tags. In
this work, we use information-theoretic measures to track the descriptive and
retrieval efficiency of tags on Stack Overflow, a question-answering system
that strictly limits the number of tags users can specify per question. We
observe that tagging efficiency stabilizes over time, while tag content and
descriptiveness both increase. To explain this observation, we hypothesize that
limiting the number of tags fosters novelty and diversity in tag usage, two
properties which are both beneficial for tagging efficiency. To provide
qualitative evidence supporting our hypothesis, we present a statistical model
of tagging that demonstrates how novelty and diversity lead to greater tag
efficiency in the long run. Our work offers insights into policies to improve
information organization and retrieval in online communities.
