Q: Complex Magma Indexed queries - draft syntax

[Brent Pinkney]

Hi Chris,

[Could you remember to send your replies to the magma mailing list]

I must confess that I have no solution yet - just early thoughts.

Problem
---------
Let us construct a hypothetical collection with indexes on attributes #a, #b, #c.

Now let use query this collection using these clauses:
	a = 'A'
	b between 'Ba' and 'Bz'
	c = 'C'

We therefore have 4 possibilities using just the AND and OR operators:

i)	a & b & c
ii)	a | b | c
iii)	(a ^ b) | c
iv)	a | (b ^ c)

Syntax
--------
Let us add convenience methods to Symbol, e.g. #at: which answers a MaClause. Then using Smalltalks cascade 
operator, the MaCollectionReader can build up a tree of clauses with the appropriate prescedence:

i)	a & b & c

	collection reader
		where: (#a at: 'A');
		and: (#b from: 'Ba' to 'Bz');
		and: (#c at: 'C');

ii)	a | b | c

	collection reader
		where: (#a at: 'A');
		or: (#b from: 'Ba' to 'Bz');
		or: (#c at: 'C');

iii)	(a ^ b) | c

	collection reader
		where: ( (#a at: 'A') or: (#b from: 'Ba' to 'Bz') );
		or: (#c at: 'C')

iv)	a | (b ^ c)

	collection reader
		where: (#a at: 'A')
		or: ( (#b from: 'Ba' to 'Bz') and: (#c at: 'C') )

Client Side MaCollection Reader Work
-------------------------------------------
As with the existing infrastructure, the reader askes each clause to compute the minimum and maximum hash values.
 
A modified tree of clauses is then serialised and submitted to the magma server.

Server Side Request Work
------------------------------
Here is where I am still very vague, but the idea is that just as with the existing queries, each clause will be able to 
find the oids between the minimum and maximum hashes.

I have no idea on performance, but could each clause not modify a bitmap index appropraitely ?

The server will then have a 2^48 (?) bit bitmap with the oids satisfying the query. This bitmap will be very sparse and 
may compress nicely. 

The server can return this bitmap and the first page of objects. 

Paging
--------
Subsequent requests from the client for pages of objects, will submit the bitmap with the request.


Comments welcome


Brent