Service providers and federated searching ...

A good federated collection is one that is accurately and consistently indexed and interoperable with other collections. I believe one of the biggest drawbacks in indexing huge collections is that very few fields will be interoperable. One way to combat that is to offer various search options to try to make up for the lowest common denominator shared by collections in a federated search.

Three service providers I examined are:
Scirus - searches more than 480 million science-related pages - harvests from some eprint repositories and some STEM publishers. A search for 'elk' retrieved 771,137 results including the accurate one elk (mammal) to Elk county to ELK as a biological pathway. The results were ordered nicely: by content provider, by file type, and subjects. Results can be ordered by relevance or date. A user has the ability to email, save, or export results. The interface and display of results is very similar to commercial products and thus in my opinion helps the user because familiarity can reduce anxiety during the search process.

NATIONAL SCIENCE DIGITAL LIBRARY -- NSDL - contains 153 unique collections of resources and over 2 million records (since sept 2008). A search for 'elk' retrieved 1020 results. The results were accurate and about elk (mammal) and ordered by K-12, Higher Ed & Research. The collection from which the item was retrieved is prominently displayed to the user. A small nuisance was that a few records returned errors and didn't display the item of interest. There is also a specialized search option where a user can run a more advanced search (i.e., by grade level, subject, and format.

BEN BiosciEdNet -- American Association for the Advancement of Science. This service is a "Pathway" for biological sciences education for NSDL. I was not able to determine what collections it draws from. A search for 'elk' retrieved only 4 matches. Various search modes are available: by subject, resource type, audience level, or advanced. Following one of the matches, I was taken to a page that required an account. As a user I am really discouraged and frustrated that a potential lead turns essentially into a dead end.