ITEMS
=====
itemid  catid  name
------  -----  ----
1       1      Master & Commander DVD
2       1      Star Wars Episode II DVD
3       2      Red Hat Linux Bible

CATEGORIES
==========
catid  name
-----  ----
1      Movies
2      Books

PERIODS
=======
periodid  name
--------  ----
1         Morning
2         Lunch
3         Afternoon

RESERVATIONS
============
rid  date      userid  periodid  itemid
---  ----      ------  --------  ------
1    02/02/05  1       1         1
2    02/02/05  2       2         1
3    02/02/05  1       3         1
...


I want to find all instances between two dates on which a specific item (or any item in a category) has not been reserved.