A few comments about SchemeQL

[Noel Welsh <noelw@dai.ed.ac.uk>]

Below are a few ideas that popped into my head while looking at
SchemeQL. I hope they're of help.

Architecture
------------

SrPersist is the only thing for now, but you don't want to be
dependent on it. I think there are four layers:

- Driver (SrPersist at the moment)
- Connection pooling (essential for performance in large systems)
- Translation from SchemeQL to SQL ('cause you will never model
vendor-specific SQL quirk in SchemeQL)
- SchemeQL

Imagine a world where SchemeQL can be used w/ SrPersist, native
drivers (faster), flat text (convenience) etc.

Selection
---------

I'd like a query to be first class object that could be parameterised,
and combined w/ intersection, union, outer join and negation to create
new queries.

Example:

Two tables in the database, one named programmers, the other
personnel:

Programmers               Personnel
employee_id   language    employee_id   employee_name
----------------------    ---------------------------
1             Scheme      1             J. A. Hacker
2             C++         2             M. Leak
                          3             B. Boss

To select all programmers:
(define programmers (query 'programmers '(employee_id language)))

To select all personnel:
(define personnel (query 'personnel '(employee_id employee_name)))


To select all (employee_name language) pairs:
(define personnel-and-language
	(intersect programmers personnel
		'(= (programmers employee_id)
		    (personnel employee_id))))

To select all (employee_name language) pairs for a given
language. That is, a query parameterised over an argument:
(define personnel-by-language
	(query (language) personnel-by-language
		'(= (personnel-by-language language) language)))

Then proceed to give all the Scheme programmers a raise:

(give-raise-to (db-find (personnel-by-language "Scheme")))

And send the C++ programmers to eternal damnation...
	   
I admit, I'm not sure how this would be implemented...

cya,
Noel
-- 
Noel Welsh
http://www.dai.ed.ac.uk/~noelw/   noelw@dai.ed.ac.uk