Best approach to create URIs with Sparql (like auto increment)

Question

I am currently writing a service which creates new items (data) by user input. To save these items in a RDF Graph Store (currently using Sesame via Sparql 1.1), I need to add a subject URI to the data. My approach is to use a number that is incremented for each new item. So e.g.:

<http://example.org/item/15> dct:title "Example Title" .
<http://example.org/item/16> dct:title "Other Item" .

What's the best approach to get an incremented number for new items (like auto incement in MySQL/MongoDB) via Sparql? Or to issue some data and the endpoint autmatically creates a URI by a template (like done for blank nodes). But I don't want to use blank nodes as subjects for these items. Is there a better solution than using an incremented number? My users don't care about the the URI.... and I don't want to handle collisions like created by hashing the data and using the hash as part of the subject.

Answer 1

If you maintain a designated counter during updates, then something along these lines will do it,

fisrt insert a counter into your dataset

insert data {
    graph <urn:counters> {<urn:Example> <urn:count> 1 }
}

then a typical update should looks like:

PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
delete {
    #remove the old value of the counter
    graph <urn:counters> {<urn:Example> <urn:count> ?old}
} 
insert {
    #update the new value of the counter
    graph <urn:counters> {<urn:Example> <urn:count> ?new}

    # add your new data using the constructed IRI
    GRAPH <http://example.com> {
        ?id dct:title "Example Title" ;
            a <http://example.org/ontology/Example> .
    } .
} where {
    # retrieve the counter
    graph <urn:counters> {<urn:Example> <urn:count> ?old}

    # compute the new value
    bind(?old+1 as ?new)    

    #construct the IRI
    bind(IRI(concat("http://example.org/item/", str(?old))) as ?id)
}