[mdx] Joe on section 3.2.1

[Ian Young]

On 30 Sep 2013, at 18:31, Tom Scavo <trscavo at gmail.com> wrote:

> On Thu, Sep 26, 2013 at 9:35 AM, Ian Young <ian at iay.org.uk> wrote:
>> 
>> ... the "+" operator in a query is equivalent to set intersection (it's defined as asking for the entity or entities that have id1 AND id2 AND id3).
> 
> In mathematics, the "+" operator is akin to union, not intersection.

I suspect the original choice of "+" was because the idea was that it was "this identifier AND that identifier" combined with "+" already being somewhat special in URLs (and therefore rarely appeared in entityID values) rather than a mathematical analogy. I can understand that it might not be completely obvious from the current text, so maybe we need to clarify it.

Or, if there is a specific objection to "+", it would be possible to pick something else as an operator. It would have to be something that didn't tend to appear in entityID values ordinarily, though, and I can't think of an alternative which would have a clearer meaning ("." is right out, obviously).

> 
>> It doesn't seem likely that you'd want to query for the intersection of a thousand named sets.
> 
> Not a thousand, but certainly more than one, especially if entity
> attributes are supported. We *are* supporting entity attributes,
> right?

It's an open issue, and we'll be coming back to it in another thread; I'd like to keep this one focused for now.

	-- Ian



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