On 14/11/2016 19:10, "Niels Andersen" <[email protected]> wrote:
Finally, regarding my list of concerns and questions. Let's start with a
specific one: Is there a SPARQL equivalent to SQL views, functions and stored
procedures? I believe that the answer is no, and if it is then what is the best
practice to provide this functionality?
For views you can use an INSERT {} WHERE {} update to create a new graph with
the data of interest eg.
INSERT
{
GRAPH <urn:temporary:example> {
?s ?p ?o
}
}
WHERE
{
# Match ?s ?p ?o as desired
}
The WHERE clause can contain an arbitrarily complex query pattern and the
INSERT clause defines a template for the new data to be created. You can then
Direct subsequent queries against that temporary graph. Once you’re done with
it every grass you can delete it with a DROP <urn:temporary:example>
Note that there is not support for views in the traditional SQL sense in most
implementations that I’m aware of. So if your data changes you would need to
rerun insert updates to recreate your temporary graphs.
In terms of functions the specifications define an extension mechanism based
upon naming functions with URIs. The range of supported functions Will vary
between implementations. You can find details on the extensions that ARQ
supports at the following page:
http://jena.apache.org/documentation/query/library-function.html
It is also possible to define and register your own functions, the mechanism
for this Will vary between vendors. Again the ARQ documentation for this can be
found at the following page:
http://jena.apache.org/documentation/query/writing_functions.html
As for stored procedures there is no support in ARQ currently nor do I believe
it is planned. Myself and Andy have discussed the idea of something similar in
the past but neither of us have been in a position to implement it. I have
seen some support for those from other vendors e.g. TopQuadrant’s SPIN but this
is not widely supported.
As Andy already implied most large applications use a business logic layer
that generates queries and updates as necessary.
Rob
