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 <> 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, $$2, etc.) - I think this could
be useful to optimize performances in implementations - what do you
think?
Giovanni
At 19.40 18/04/2008, Markus Sabadello wrote:
Hmm no, right now the query
engine only selects input statements that fully match a query statement.
So if a query statement contains only a subject and a predicate, then it
will only select input statements with only subject and predicate, not
input statements with subject, predicate and something else.
So even if you just want to know everything about =giovanni, you would
have to enter
=giovanni
$$
$$
instead of just
=giovanni
The latter will only work in my implementation of XDI messaging, but not
in the XDI query engine.
But maybe it should work that way too?
Markus
On Fri, Apr 18, 2008 at 6:20 PM, Giovanni Bartolomeo
<
> wrote:
Hello Markus,
thanks for this update. It has been great to see the querier at work
yesterday!
Simple question regarding this query:
At 00.43 18/04/2008, Markus Sabadello wrote:
=giovanni
+friend
$$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
