There is no need to lock the whole document, just that part of the document
that consititutes an updatable record for the database it is being used to
update or being updated from. Such a record could consist of a a number of
contiguous fields, a set of discrete fields taken from appropriate parts of
a document, or even a single field. There in no reason why fields not likely
to be affected by change need to be locked in any way.
Martin Bryan