Thanks for the comment. I wasn't necessarily making any assumptions about the difficulty of indexing . I do appreciate (at least to some degree) the challenge of indexing the journal citations.
I have previously parsed the xml citations and loaded them into a relational database. However, I've recently come across a number of references to Lucene/Solr, and it appears that more people are using it for this type of task. I'm thinking that maybe this is a better approach than the way I was originally doing it. I have no background in this area, so I'm just trying to solicit some guidance or anecdotes from others who have done similar things (with MEDLINE/PubMed is a bonus).
I will search the literature to see if I can find some useful information to get me started.
Thanks.