Hi All. I just uploaded the latest version of Dmitriy Arapov's and my Relational Template Library (RTL) to the Boost file vault, http://tinyurl.com/8lbmg. This version is compatible with Boost 1.33. The RTL was discussed on this list at some time in the past. The early version of RTL is described in the March 2004 issue of CUJ. The main difference from currently discussed RML is that we decided against using SQL - like interface, and use the relational algebra-based interface instead. This choice is caused by our belief that the optimizer -- the module converting SQL query into an optimized relational expression -- is one of the most sophisticated parts of modern database engines. Also, writing a good optimizer in a system like RTL (or RML) would have to be done in large part at compile time, by the means of template meta-programming. This task doesn't seems to be feasible, at least currently. OTOH, writing a primitive optimizer, would, in our opinion do more harm than good. So, the RTL gives its user the possibility to build arbitrary relational expressions by hand. We augment the pure relational algebra with a few things, such as sort order, indexing, groupby, join, etc. We also allow indexing of any relational expressions, not just tables. So, for example, a user can do a selection on some arbitrary complicated criteria, and then index this selection. This would ultimately result in the index storing just keys to these records. This index would be incrementally updated when the underlying table has been changed. Achieving the same effect with conventional approach would require creation of a much larger index on a calculated field. Another example -- you have table of cities, and you need to get all the pairs, such as the distance between them is less than certain number. How would one solve the problem with the conventional SQL approach? This is a self-join. But how to make this query fast? With RTL approach, we could create an index on this self-join. The RTL can currently be compiled with VC7.1 or GCC 3.3+ (although with GCC there might still remain some naming conflicts between MPL and STL, that show up with certain usages) Regards, Arkadiy