Generating unique ID's in triple-store, ala MySQL AUTO_INCREMENT

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#1

I'm under increasing pressure to start using RDF as a back-end for websites, rather than MySQL.

I've been considering the basic "patterns" of use, generally they boil down to create item, delete item, update item, get-from-id, get-items-matching-x.

In MySQL, when creating an item, we use an AUTO_INCREMENT field to be sure we get a unique ID. Is there a reliable way to do this with a triple-store as a backend?

I don't want to generate UUID's (although thanks for the suggestion), we often need to expose primary keys in URLs. eg: http://foobar.com/news/134.html I don't want to have to use: http://foobar.com/news/12Ef0023-F238EbA673CAA38-F34.html It's not user-friendly.

#2

Is this necessary? I would assume that each triple's dereferencable URL would be a unique (though not necessarily incremented) id :)

This approach allows you to abstract away from the storage.

#3

When using virtuoso you can use the fact that it is also a rdbms to use its internal atomic sequences. With something like this.

SPARQL INSERT INTO GRAPH <http://mygraph.com> {  
        <:a>
        <:p>
        sql:sequence_next("GRAPH_IDENTIFIER") };

See http://docs.openlinksw.com/virtuoso/sequenceobjects.html and http://docs.openlinksw.com/virtuoso/rdfsparql.html#rdfsqlfromsparql

To be honest I have not tested it yet. I will try this tonight. In practice you might need to do a separate select for key and then insert later as you might need the key directly in your front-end application.

#4

Just an idea: how about GUIDs? I hear they are increasingly common in the RDBMS land as well. Maybe they are more expensive to produce and locate than integers, but you don’t have to care about concurrency.

#5

By 'a reliable way' do you mean 'a way that makes the data store enforce it natively'? If so, then I believe that the answer is No.

#6

Would it be hard to just store the value in a triple and handle an auto-increment mechanism that update it ? or a select max ? (also handling concurrence)

Sorry if that is stupid...but a few years back, we did the same with a DB that didn't handle auto-increment, it was just fine...

#7

It's not quite triple-store only, but you could use a redis instance to look after your sequence in a non-racy kinda way. That way, whenever you need to create a new identifier you can perform an INCR command to get the unique integer you want to stick in your URIs.

#8

Here are some links that might give you some ideas: