Hi Claude,
On 09/01/17 10:55, Claude Warren wrote:
I am digging into reasoners for the first time in a long time and have a
couple of questions.
What I am trying to do is the following:
Assume data:
<x> <my:sameValue> <y>
<y> <my:value> 5
I want a rule that will produce
<x> <my:value> 5
So something like:
(?x my:sameValue ?y) (?y my:value ?v) -> (?x my:value ?v)
but in addition if I change [<y> <my:value> 5] to [<y> <my:value> 10] I
want the reasoner to change [<x> <my:value> 5] to [<x> <my:value> 10]
So after first reasoning data are:
<x> <my:sameValue> <y>
<y> <my:value> 5
<x> <my:value> 5
and after changing <y> <my:value> 5 the data are:
<x> <my:sameValue> <y>
<y> <my:value> 10
<x> <my:value> 10
Note that the <x> <my:value> 5 has been deleted.
Is this possible?
Sure, it would work that way so long as the [<y> <my:value> 5] is only
present by virtue of the inference, not in the base graph (see below).
In general do rules recalculate the results when the data changes?--
Yes but deletes are not incremental, and the details differ between the
reasoners.
The forward reasoners keeps a graph of partial bindings and if new
triples are added the additional inferred triples are computed
incrementally. If a triple is removed then the graph is marked unclean
(the "prepared" flag is reset) so at the next query (or next explicit
prepare() call) the inference will be restarted from scratch.
So in your case, starting with a base model of:
<x> <my:sameValue> <y>
<y> <my:value> 5
then the above rule would generate a deduction of:
<x> <my:value> 5
If you then delete:
<y> <my:value> 5
and add:
<y> <my:value> 10
Then, at the next query, the forward reasoner will throw away its
deductions graph and internal rete network and start over, it would then
generate:
<y> <my:value> 5
However, if your base graph had:
<x> <my:sameValue> <y>
<y> <my:value> 5
<x> <my:value> 42
then the rules won't remove that third triple so you would end up with:
<x> <my:sameValue> <y>
<y> <my:value> 5
<x> <my:value> 42
<x> <my:value> 5
For the backward rules then, unless you use tabling to cache partial
goals, the inference is done on demand at query time anyway so you'll
get the same answers as above and the work will be done again at each
query whatever you've done to the graph in the meantime.
Dave
