Lucene has a pretty well-specified search syntax which is unlikely to change all that much, even though it's not a standard.  It's not perfect, but I think it's pretty good.  Overview here:
 
http://lucene.apache.org/java/docs/queryparsersyntax.html 
 
I believe Solr adds a bit to the standard Lucene syntax for sorting:
 
http://incubator.apache.org/solr/tutorial.html#Sorting 
 
I do have a layer of abstraction between the end-user search interface and Lucene -- you'd have to have such a layer no matter what search engine you were using.
 
 
>>> [log in to unmask] 11/27/2006 2:49 PM >>>
Casey Durfee wrote:
>
>Just using Solr has proven to be much faster than doing the search in Solr and then retrieving full data from another database.  This also has the advantage of making it so there's only one thing you gotta keep in sync with the ILS.  The only data that my OPAC needs to talk to a SQL database for is item-level information, which changes too often to keep synced.
>
My only concern about lucene is the lack of a standard query language.
I went down the native XML database path because of XQuery and XSL, does
something like lucene and solr offer a strong query language?  Is it a
standard?  What if someone developed a kick ass text indexer in 2 years
that totally blows lucene out of the water, would you easily be able to
switch systems?

Andrew