[mdx] Joe on section 3.2.1

[Tom Scavo]

On Mon, Sep 30, 2013 at 3:07 PM, Ian Young <ian at iay.org.uk> wrote:
>
> 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.

Yes, it's a misnomer, so it could use some clarification.

> 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

I can't think of a better notation either. A space between IDs aligns
with standard mathematical notation but that leads to ugly URLs IMO.

Tom