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Re: [WebSQL] Any future plans, or has IndexedDB replaced WebSQL?

From: Keean Schupke <keean@fry-it.com>
Date: Mon, 4 Apr 2011 15:55:24 +0000
Message-ID: <BANLkTimV0i3a4QmxSS83UXWvjmozTm8dSA@mail.gmail.com>
To: Joran Greef <joran@ronomon.com>
Cc: public-webapps@w3.org
Yes, it already has well defined set operations. Solid is a matter of
testing by enough people (and if you wanted to try it and feed back that
would be a start). Fast should not be a problem, as the SQL database does
all the heavy lifting.

In more detail, Codd's six primitive operators are project, restrict,
cross-product, union and difference. Relations are an extension of Sets, so
intersection and difference on compatible relations behave like they would
on sets.

RelationalDB already implements the following 5 methods making it
relationally-complete. Meaning it can do anything you could possibly want to
do with relations using combinations of these 5 methods.

    Relation.prototype.project = function(attributes) { // this implements
rename as well.
    Relation.prototype.restrict = function(exp)
    Relation.prototype.join = function(relation, exp) {
    Relation.prototype.union = function() {};
    Relation.prototype.difference = function() {};

Of course some things can be made easier, so the following methods, although
they can be defined in terms of the above 5, will be provided (in future
implementations) to keep user code concise and implementations thin and

    // derived methods
    Relation.prototype.intersection = function() {};
    Relation.prototype.thetajoin = function() {};
    Relation.prototype.semijoin = function() {};
    Relation.prototype.antijoin = function() {};
    Relation.prototype.divide = function() {};
    Relation.prototype.leftjoin = function() {};
    Relation.prototype.rightjoin = function() {};
    Relation.prototype.fulljoin = function() {};

We also hope to provide the lattice operators "meet" and "join":


Just these two operators can replace all 5 of Codd's primitives (including
all set operations). With just these two you can do anything that you can
with _all_ the above. Meet is actually the same as Codd's natural-join
(unfortunately terminology in different mathematical fields is not
consistent here) and Join is a generalised union operator.



To see how Meet and Join can be used to construct each of the above


On 4 April 2011 15:36, Joran Greef <joran@ronomon.com> wrote:

> On 04 Apr 2011, at 5:26 PM, Keean Schupke wrote:
> > This is ignoring the possibility that something like RelationalDB could
> be used, where a well defined common subset of SQL can be used (and I use
> well-defined in the formal sense). This would allow a relatively thin
> wrapper on top of most SQL implementations and would allow SQLite (or BDB)
> to be used as the backend.
> Yes, if an implementation of RelationalDB arrives which is solid and fast
> with support for set operations that would be great. The important thing is
> that we have two competing APIs (and preferably a strong API with a great
> track record).
Received on Monday, 4 April 2011 15:56:00 UTC

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