Hi,
On December 15 (01:45 +0000), Michael Hobbs wrote with possible deletions:
| Tom Pledger wrote:
| > In the last 12 months or so, all the database-related messages in this
| > list have involved interfacing to SQL engines. By contrast, how about
| > using Haskell as a non-SQL relational database language?
|
| I've always thought that a functional language such as Haskell would
| provide a very good framework for using relational algebra in order to
| combine and extract data. (In contrast to using something like a
| Structured Query Language.) I dabbled with this a bit, but didn't get
| very far before I lost interest. :)
You might be interested in our work on mapping SQL (resp. OMDG's OQL)
to the monad comprehension calculus and, subsequently, a combinator
representation that is finally cheaply deforested to obtain a---how
the database folks call them---streaming program from an algebraic
query. The streaming paradigm of query evaluation and the notion of
tree-less functional programs are remarkably close, IMHO.
A broad range of heuristic query optimization approaches turn out to
be simple rewriting steps in the monad comprehension calculus. That's
esp. true for queries involving aggregates, grouping, and
quantification (but for the vanilla select-from-where query as well),
ie. for a class of queries which isn't mapped easily (if at all) to a
"classical" relational algebra.
If anyone is interested, details on all stages of the query
compilation and optimization process in such a purely functional
framework are described in a range of articles that can be found
hanging off my homepage.
I also recommend to have a look at Leonidas Fegaras' (Univ of Texas,
Arlington) excellent work in this area (http://lambda.uta.edu/).
Best wishes,
--Torsten
P.S. The connection between the database and FPL communities is
quite tight, IMHO. It always has been (the functional data model
[Shipman et al.] dates back to the 70's), and it is today: Kluwer
publishes a Special Issue of its JIIS on the ``Functional
Approach to Intelligent Information Systems'' early next year.
--
| Torsten Grust [EMAIL PROTECTED] |
| http://www.fmi.uni-konstanz.de/~grust/ |
| Database Research Group, University of Konstanz (Lake Constance/Germany) |
