From: "Jonathan Rochkind" <rochk...@jhu.edu>
Another question though. I note when looking up schemaInfo... I'm a bit
confused by the "sort" attribute. How could you sort by a schema? What is
this attribute actually for?
Well indulge me, this is best explained by the current OASIS SRU draft.
(The current and earlier specs don't do a good job here. But for background
if interested: sorting as an SRU function was supported in SRU 1.1 and
taken out of version 1.2, replaced by sorting as a function of the query
language rather than the protocol. For the OASIS work it's in both. For the
current spec at LC, which reflects 1.2, the attribute doesn't even make
sense. If you go back to the 1.1 archive it does. Still, the OASIS document
treats it more clearly.)
See http://www.loc.gov/standards/sru/oasis/sru-2-0-draft-most-current.doc
See section 9.1.
So essentially, when you sort in SRU, you provide an XPath expression. The
XPath expression is meaningful in the context of a schema, but the *record
schema* may not be the most meaningful schema for purposes of sorting, there
may be another schema more meaningful. So, you have the capability to
specify not only a record schema but an auxiliary sort schema.
A given schema that an Explain file lists will usually be one that is used
as a record schema, but it may also be usable as a sort schema. That's
what the sort attribute tells you.
--Ray
