The purpose of this middleware is to find availablity for items that are electronic. The API that can return information about these items is a hosted service run by SFX.
A good way to see examples of the service in use it to visit SOLO, http://solo.ouls.ox.ac.uk/, search for a item in the Journal Articles section and then click on the additional services tab for one of the results. Clicking on the “Open source in a new window” pops it out and allows you to see the URL. Next add &sfx.response_type=simplexml to the end of the URL and you get back details about the item. As an example try http://preview.tinyurl.com/5sosem7 .
The idea is that EIAS will receive a request for details about an item, rather than being passed a URL, it will get an OpenURL, which it can send through to the SFX service and then translate the returned response to DAIA to that the client can parse and easily understand it.