[dotNetRDF-Develop] Spaqrl Query Performance

[Fedja A. <ad...@ad...>]

Hello dotNetRDF Team,

I'm quite new to your library and RDF as well, and I have run into some 
performance issues I don't seem to be able to solve by myself. Not being 
sure whether this is a problem on my side or simply an algorithmic or 
implementation issue, I'm writing you for some feedback and / or help.

The setup is reasonably simple: I'm using an InMemoryDataset consisting 
of (potentially multiple, but in this case a single) Graph(s). The 
dataset is very small (73 lines of Turtle) and the queries I'm 
performing shouldn't be too complex either. This is the code I'm using 
for querying:

    SparqlParameterizedString queryString = new SparqlParameterizedString();
    queryString.CommandText = query;
    // []Adding namespaces here]
    // [Setting parameters here]
    SparqlQuery sparqlQuery = this.parser.ParseFromString(queryString);
    SparqlResultSet resultSet = this.processor.ProcessQuery(sparqlQuery)
    as SparqlResultSet;

I'm using a SparqlQueryParser and a LeviathanQueryProcessor. Everything 
happens locally on my machine, no web stuff involved. The problem is 
that *a single ProcessQuery call takes about **5 - 7 ms*, which is too 
much for my purposes. I need to perform a lot of differently 
parameterized queries in a row.

*Is there any way I could improve performance?* Calling "Optimize" on 
the query before executing doesn't seem to have an effect. A 
representative example query is this one:

    SELECT ?obj
    WHERE
    {
       ?obj Knowledge:IsA* ?actor .
       ?actor Knowledge:HasAttribute Knowledge:Actor .
       ?obj Knowledge:IsA* ?prey .
       @MainActor Knowledge:PredatorOf ?prey .
       MINUS
       {
         ?obj Knowledge:HasAttribute Knowledge:Abstract .
       }
       FILTER (!sameTerm(?obj, @MainActor))
    }

If you spot any wild problems in the query itself, let me know.

I've also looked at some parts of the RDF Querying code and it seems 
like there is some kind of Algebra evaluation using classes - is there 
maybe a way to "Compile" them similar to C# Expression trees in order to 
improve performance?

Regards,
Adam