Re: [topbraid-users] defining a SPIN function that returns multiple variables

Scott Henninger Thu, 09 May 2013 11:26:19 -0700

Allison; Since the AnotherExample:ScoreAttendedCollege returns one value, not a set of values (multiple rows) or a list of values (multiple columns), then the best choice is to use a SPIN function. Change the type of :ScoreAttendedCollege to spin:Functions and use in a BIND or projection:

SELECT ?score
WHERE {
BIND(AnotherExample:ScoreCollege("John") AS ?score).
}

...and the projection version would be as follows:

SELECT (AnotherExample:ScoreCollege("John") AS ?score)
WHERE {}

These translate into the exact same SPARQL algebra, so it's a matter of preference which one you use.

For your magic property, I think you just got it backwards the subject of the magic property are the variables bound in the WHERE clause. The object are the selected variables. So I think the following will work:

SELECT *
WHERE {
("John") AnotherExample:ScoreCollege (?score) .
}

-- Scott

On 5/9/2013 10:42 AM, Alison Callahan wrote:

Hi Scott,

Thanks for your detailed reply. I successfully followed your MagicExample:FindNamesOfCollegeGrad example.

I have a follow-up question, based on another thread: If I use a magic property in the spin:body of another magic property, and there is more than one result when the magic property is executed, how can I retrieve all of the results?

For example, when John Kennedy is passed in to the FindNamesOfCollegeGrad magic property in a SPARQL query, i.e.

SELECT *
WHERE
{ ?person a kennedys:Person .
   ?person kennedys:almaMater ?college .
   (?person ?college) MagicExample:FindNamesOfCollegeGrad ("John" ?middle ?last)
}

there are two results for ?college: kennedys:Harvard and kennedys:Princeton.

Now let's say I have another magic property called 'AnotherExample:ScoreAttendedCollege' where a first name is passed in as ?arg1 and the spin:body of the property is:

SELECT ?collegeScore

WHERE

{

   (?person ?college) MagicExample:FindNamesOfCollegeGrad (?arg1 ?middle ?last) .

BIND(IF((?college = kennedys:Princeton), 1, 0) AS ?collegeScore) .

}

In other words, if the person with the specified first name attended Princeton, return a score of 1, else return a score of 0.

I created this magic property, but when I use it in a SPARQL query as follows:

SELECT *
WHERE {
(?score) AnotherExample:ScoreCollege("John") .
}

there are no results. However, if I use it in a SPARQL query this way:

SELECT ?score
WHERE {
BIND(AnotherExample:ScoreCollege("John") AS ?score).
}

the result of the query is 0. My hunch is that this is because only the first bound result (kennedys:Harvard) was evaluated by the 'AnotherExample:ScoreCollege' magic property, i.e. the kennedys:Princeton result is never evaluated because the iteration seems to break. Is this correct?

How can I use AnotherExample:ScoreCollege to return the score for each value bound to the ?college variable returned by the MagicExample:FindNameOfCollegeGrad magic property? If I can't use BIND within a magic property to assign a value based on the result of an embedded magic property, what alternatives exist?

Thanks again!

Alison

On Wed, May 8, 2013 at 4:11 PM, Scott Henninger <[email protected]> wrote:

Allison, probably the best way to learn magic properties is by example. In the Composer navigator, go to TopBraid/Examples/kennedysSPINMagic.ttl and open that.

In the Classes view find spin:MagicProperties. A Magic property is a subclass of spin:MagicProperties. You can see the body of the definition for age (after running inferences), grandfather, and grandMother. These are used in SPARQL as a property that instead calls the body of the query (hence a "magic" property).

An example, let's say you want to find a grandfather:
SELECT *
WHERE
{   ?person a kennedys:Person .
    ?person kspin:grandFather ?gf
}

Note you can use this magic property either way. So to find all grandchildren of Joe Kennedy:
SELECT *
WHERE
{    ?gchild kspin:grandFather kennedys:JosephKennedy
}

I know, I haven't answered the question yet. For multiple parameters of values, use a list structure (see, for example top:files in Help > TopBraid Composer > Reference > SPARQL Property Functions). As an additional example, I've added an example in the attached file to define a magic property named MagicExample:FindNamesOfCollegeGrad (kinda a silly example, buyt it gets the idea across)

You can use it this way for example:

SELECT *
WHERE
{ ?person a kennedys:Person .
   ?person kennedys:almaMater ?college .
   (?person ?college) MagicExample:FindParentsOfCollegeGrad (?first ?middle ?last)
}

You can bind/not bind any of the input parameters or output values. For example to find all John's try this.

SELECT *
WHERE
{   ?person a kennedys:Person .
   ?person kennedys:almaMater ?college .
   (?person ?college) MagicExample:FindParentsOfCollegeGrad ("John" ?middle ?last)
}

Given that as an interesting example to explore, let us know if that answers the question or if you have follows.

-- Scott

On 5/8/2013 11:51 AM, Alison Callahan wrote:

Hi Holger,

I have looked at Magic Properties, and thought they were relevant to my question, but I couldn't find any examples of how to create a magic property that returns multiple values. On the page you linked to, it says "Magic properties can also take multiple arguments and result values using a (rather obscure) list syntax - these cases are technically supported but complex to represent in the SPIN RDF syntax".

Could you provide more detail or a link that describes this list syntax for creating a magic property that returns multiple values?

Thanks!

Alison

On Mon, Apr 29, 2013 at 7:00 PM, Holger Knublauch <[email protected]> wrote:

Hi Allison,

yes take a look at Magic Properties

http://spinrdf.org/spin.html#spin-magic

These may not only return multiple "rows" but also multiple variables per row.

Please take a look at the online material and get back to us if you have specific follow-up questions.

HTH
Holger

On 4/30/2013 1:01, Alison Callahan wrote:

Hello all,

I would like to be able to define the body of a SPIN function that returns two variables, e.g.

SELECT ?x ?y
WHERE {
?example test:x ?x .
?example text:y ?y .
}

My question is: if such a function is possible, how are the results bound when the function is called? In my experience with SPIN I have written functions that return one variable, and thus the result is bound to a single variable when the function is called. For example, if I have a SPIN function called "functionA" where the spin:body is:

SELECT ?a
WHERE {
?example test:a ?a .
}

I would call this function and bind the result as

BIND(:functionA(?aVariable) AS ?returnedA) .

Is it possible to write a similar function that returns two (or more) variables?

Any help is appreciated!

Alison

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Re: [topbraid-users] defining a SPIN function that returns multiple variables

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