~ Simultaneous search and retrieval "players" are the resource, the search software, the user ...and the means by which they "talk."

~ Predominant method/standard is Z39.50

~ Others are HTTP "screen-scraping" and proprietery APIs

~ NISO's MetaSearch Initiative:

"The absence of widely supported standards, best practices, and tools makes the metasearch environment less efficient for the system provider, the content provider, the library, and ultimately the end-user."

~ Under development - XML based protocol: SRW/U (Search/Retrieve Web/URL service)