Holger: I have a followup question. Creating a SPIN function that performs
the summation works well for computing a single sum to be passed back as
the function's return value. In my actual case, I'm trying to calculate
multiple sums and return them. While I could write a more general function
(or template) and call it several times to compute several sums, that is
quite inefficient because it will require performing essentially the same
SPARQL Select N times, once for each datatype property I wish to sum over.
Can you suggest an alternative approach that would be more efficient?
Thanks for your help,
Rich
On Tuesday, March 18, 2014 9:25:30 AM UTC-7, Rich Keller wrote:
>
> Thanks Holger. I will try that. Rich
>
> On Monday, March 17, 2014 3:57:32 PM UTC-7, Holger Knublauch wrote:
>>
>> Hi Rich,
>>
>> in general, nested sub-selected do not see the bindings of variables from
>> the outer query. If you want to perform an aggregation, try turning the
>> inner SELECT into a SPIN function where you can explicitly pass the
>> required arguments. E.g. the spin:body of that function ex:myCount would be
>>
>> SELECT ((SUM(?hourlyCount)) AS ?dailyCount)
>> WHERE {
>> ?arg1 :xday ?day . #Should bind ?day to the :xday value
>> for the specific instance over which the rule is firing
>> ?hourly :day ?day .
>> ?hourly :count ?hourlyCount .
>> }
>>
>> where ?arg1 is substituted with ?this when you call it in the rule:
>>
>> CONSTRUCT {
>> ?this :xcount ?dailyCount .
>> }
>> WHERE {
>> BIND (ex:myCount(?this) AS ?dailyCount) .
>> }
>>
>> HTH
>> Holger
>>
>>
>> On 3/18/2014 8:37, Rich Keller wrote:
>>
>> Hi. I have been having trouble with a SPIN rule I've constructed to
>> aggregate a set of values. It seems as if the variable ?*this* is not
>> being bound properly, and I wonder if this is due to my SPARQL formulation
>> or to TBC.
>>
>> Here is the problem. Conceptually, there are counts of a particular
>> phenomenon occurring on a given day during a given hour: <day, hour,
>> count>. The rule's task is to sum the counts for each hour, and assign that
>> sum to the count for the appropriate day. The SPIN rule is defined for a
>> 'Daily' object (representing a day); the counts are assigned to 'Hourly'
>> objects (representing an hour of a particular day).
>>
>> I assumed that the aggregation function SUM (in the rule below) would sum
>> over only the counts for a single day, because I constrained the variable
>> ?day using ?*this*. However, the results indicate that the day was not
>> constrained because the sum for each day is the same: the grand total of
>> all counts over all days. Perhaps I do not understand the scoping rules for
>> ?*this* within the SPARQL expression.
>>
>> Any guidance would be appreciated! When I execute the SELECT clause alone
>> in the SPARQL Query Editor, substituting a specific 'Daily' instance for ?
>> *this*, I do get the desired sum for the hours in that day.
>>
>> Thanks,
>> Rich
>>
>>
>> :Daily a owl:Class ;
>> spin:rule
>> "CONSTRUCT {
>> ?this :xcount ?dailyCount .
>> }
>> WHERE {
>> {
>> SELECT ((SUM(?hourlyCount)) AS ?dailyCount)
>> WHERE {
>> ?this :xday ?day . #Should bind ?day to the :xday value
>> for the specific instance over which the rule is firing
>> ?hourly :day ?day .
>> ?hourly :count ?hourlyCount .
>> }
>> } .
>> }"
>>
>> :D1 a :Daily;
>> :xday 1 .
>>
>> :D2 a :Daily;
>> :xday 2 .
>>
>>
>> :Hourly a owl:Class .
>>
>> :H1D1 a :Hourly;
>> :count 10 ;
>> :hour 1 ;
>> :day 1 .
>>
>> :H2D1 a :Hourly;
>> :count 10 ;
>> :hour 2 ;
>> :day 1 .
>>
>> :H3D1 a :Hourly;
>> :count 10 ;
>> :hour 3 ;
>> :day 1 .
>>
>> :H1D2 a :Hourly;
>> :count 10 ;
>> :hour 1 ;
>> :day 2 .
>>
>> :H2D2 a :Hourly;
>> :count 10 ;
>> :hour 2 ;
>> :day 2 .
>>
>> ----------------
>>
>> Inference Result:
>>
>> :D1 :xcount 50
>> :D2 :xcount 50
>>
>> Expected Result:
>>
>> :D1 :xcount 30
>> :D2 :xcount 20
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