  A growing number of astronomical resources and data or information services
are made available through the Internet. However valuable information is
frequently hidden in a deluge of non-pertinent or non up-to-date documents. At
a first level, compilations of astronomical resources provide help for
selecting relevant sites. Combining yellow-page services and meta-databases of
active pointers may be an efficient solution to the data retrieval problem.
Responses generated by submission of queries to a set of heterogeneous
resources are difficult to merge or cross-match, because different data
providers generally use different data formats: new endeavors are under way to
tackle this problem. We review the technical challenges involved in trying to
provide general search and discovery tools, and to integrate them through upper
level interfaces.
