  Interactive query expansion can assist users during their query formulation
process. We conducted a user study with over 4,000 unique visitors and four
different design approaches for a search term suggestion service. As a basis
for our evaluation we have implemented services which use three different
vocabularies: (1) user search terms, (2) terms from a terminology service and
(3) thesaurus terms. Additionally, we have created a new combined service which
utilizes thesaurus term and terms from a domain-specific search term
re-commender. Our results show that the thesaurus-based method clearly is used
more often compared to the other single-method implementations. We interpret
this as a strong indicator that term suggestion mechanisms should be
domain-specific to be close to the user terminology. Our novel combined
approach which interconnects a thesaurus service with additional statistical
relations out-performed all other implementations. All our observations show
that domain-specific vocabulary can support the user in finding alternative
concepts and formulating queries.
