Re: [xdi] XDI Querier update

["Markus Sabadello" <markus.sabadello@xdi.org>]

Heya,

Yes I agree it makes sense to have "unbound" $$ variables.

However, in my current implementations they are not faster than "bound" ones (maybe they could be - don't know). In fact, before I even start executing the query, I replace them with automatically generated, negative "bound" ones, i.e. $$-1, $$-2, $$-3, etc. So when I execute the query, I don't have to treat them differently.

By the way, I think queries always have two kinds of results:
1) One result graph, which contains all statements of the input graph that somehow matched the query
2) Zero or more result variable value maps, which contain all combinations of variable values that were used to apply the query

For example, if you execute this query:
$$
    +age
        "30"

The the result graph is:
=aria.giovanni
    +age
        "30"
=marco
    +age
        "30"

And the result variable value maps are:
Variable value map 1: $$ -> =aria.giovanni
Variable value map 2: $$ -> =marco

This is useful if you are just interested in "who is 30 years old", not in the whole result graph.

Because of these variable value maps I don't think $$ can be made faster than $$1, $$2, $$3, etc., because the variable values have to be "recorded" in both cases while executing the query, but I still agree that $$ should exist simply because it makes it easier to write a query :)

Markus

On Mon, Apr 21, 2008 at 3:50 PM, Giovanni Bartolomeo <giovanni.bartolomeo@uniroma2.it> wrote:

Thanks Markus,

apart from the implementation, maybe in the specification we should allow both forms. One question may arise about the usefulness of $$ if we allow the first form; well the answer may be a thing like this:

$$
   +age
         "25"

of course we could anyway use $$1 instead of $$ here, but I would prefer to have an explicit different form for the unbounded variable ($$) than the one used for the bounding ones ($$1, $$2, etc.) - I think this could be useful to optimize performances in implementations - what do you think?

Giovanni

At 19.40 18/04/2008, Markus Sabadello wrote:

Hmm no, right now the query engine only selects input statements that fully match a query statement. So if a query statement contains only a subject and a predicate, then it will only select input statements with only subject and predicate, not input statements with subject, predicate and something else.

So even if you just want to know everything about =giovanni, you would have to enter

=giovanni
    $$
        $$

instead of just

=giovanni

The latter will only work in my implementation of XDI messaging, but not in the XDI query engine.

But maybe it should work that way too?

Markus

On Fri, Apr 18, 2008 at 6:20 PM, Giovanni Bartolomeo < giovanni.bartolomeo@uniroma2.it> wrote:

Hello Markus,

thanks for this update. It has been great to see the querier at work yesterday!

Simple question regarding this query:

At 00.43 18/04/2008, Markus Sabadello wrote:

=giovanni

   +friend

       $$1

($$1/+age)

   $equals$or$lesser

       "26"

$$1

   +sister

       $$2

$$2

   +nationality

       $$

($$2/+nationality)

   $equals

       "Italian"

is it the same to ask

$$2

  +nationality

instead of

$$2

  +nationality

       $$

?

Giovanni