Hi Scott,
Thanks very much for this information. There is one other thing I wonder
about spin which is this: If a class has a spin:rule and a member of that
class is deleted or changed, will any extra triples created by the
spin:rule be removed or does the system have to manually clear out the dead
triples?
Mark
On Wednesday, June 20, 2012 1:59:51 AM UTC+1, Scott Henninger wrote:
>
> Mark; In addition to "magic" properties, I'd suggest taking a look at
> functions. This is a step in the same direction (reusable SPARQL
> queries). The same general concept. Start by creating a subclass of
> spin:Functions. Let's say you name the subclass ":GetCurrentYear".
> Then enter the following simple query in the spin:body property:
>
> SELECT ?year
> WHERE
> { BIND(year(now()) AS ?year)
> }
>
> You can run this query on its own and will find that it returns the
> current year - 2012. Now in any SPARQL context for that model, you
> can enter the following:
>
> SELECT *
> WHERE
> { BIND(:GetCurrentYear() AS ?year)
> }
>
> The is will call the body of the aforementioned query. Not much here,
> but you can also pass parameters to it as spin:constraints. (You can
> also make this a globally defined function for your workspace by
> adding a .spin name to register the function - i.e.
> myCommonDefs.spin.ttl.) Go back to the previous query and create an
> argument by choosing "Create from SPIN Template". Fill in the
> predicate with sp:arg1 and set its type to xsd:string.
>
> Now you define the body to take that argument, which is named after
> the local name when used in the query - i.e. ?arg1. Let's just create
> a string from the above as a kind of "Hello World" example:
>
> SELECT ?year
> WHERE
> { BIND(fn:concat(?arg1, year(now())) AS ?year)
> }
>
> Now you can pass a value to the function, such as:
>
> SELECT *
> WHERE
> { BIND(:GetCurrentYear("The current Year is: ") AS ?year)
> }
>
> ...and the result is "The current year is: 2012". Of course, you can
> do any bit of SPARQL with the function definition - graph patterns,
> call other functions, etc. But this is meant as a universally
> accessible "Hello World" while exposing some of the less-well-known
> data processing elements of SPARQL. The function differs from a magic
> property in that it acts as a function call - returns a single value
> for each call. And this is usually enough when combined with the
> graph pattern matching of SPARQL. Sometimes one needs to return
> multiple values, or want a function to act like a triple pattern -
> i.e. a virtual or computed property (the term "magic property" is
> admittedly an ill-defined way to describe this functionality), and it
> is only then that magic properties are needed.
>
> There is much more on this and other SPIN definitions at
> http://www.topquadrant.com/products/SPIN.html
>
> -- Scott
>
> On Jun 19, 8:26 pm, Holger Knublauch <[email protected]> wrote:
> > On 6/20/2012 10:18, Mark Green wrote:
> >
> > > Hi,
> >
> > > I'm having some trouble trying to define a SPIN Magic Property. I can
> > > create a new property that is an instance of spin:MagicProperty but
> > > when I open the spin:body property to enter the query, it doesn't
> > > allow me to enter the query, it instead wants me to choose an
> > > instance. Do I have to build the SPIN equivalent of the SPARQL query
> > > manually for a Magic Property?
> >
> > Hi Mark,
> >
> > use Add empty row to enter a SPIN query for spin:body. This should work.
> > (Use Shift-enter for line breaks).
> >
> > BTW to define a new magic property I don't recommend simply to create an
> > instance of spin:MagicProperty. It also should to be a subclass of
> > spin:MagicProperties. So the easiest way to achieve that is to open the
> > class tree spin:Modules > spin:Functions > spin:MagicProperties, then
> > right-click on spin:MagicProperties and create a subclass of that.
> >
> > Thanks
> > Holger
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