private HashSet <Tuple> SelectFromRemainingClauses(RequestProcess process, Tuple partial, int startIndex)
{
HashSet <Tuple> tuples;
HashSet <Tuple> result;
Clause clause = this.Clauses[startIndex].Clone();
// Fill in the clause with values from the tuple under consideration.
string value;
if (clause.subj.StartsWith("?") && partial.TryGetValue(clause.subj, out value))
{
clause.subj = value;
}
if (clause.pred.StartsWith("?") && partial.TryGetValue(clause.pred, out value))
{
clause.pred = value;
}
if (clause.obj.StartsWith("?") && partial.TryGetValue(clause.obj, out value))
{
clause.obj = value;
}
// Find triples that match.
var triples = process.Bot.Triples.Match(clause);
if (!clause.Affirm)
{
// If the notq assertion succeeds, we just add the tuple under consideration without filling in any variables.
if (triples.Count != 0)
{
return(new HashSet <Tuple>());
}
tuples = new HashSet <Tuple>();
tuples.Add(partial);
}
else
{
// Add possible tuples from each matching triple.
tuples = new HashSet <Tuple>();
foreach (var tripleIndex in triples)
{
var tuple = new Tuple(partial);
if (clause.subj.StartsWith("?"))
{
tuple.Add(clause.subj, process.Bot.Triples[tripleIndex].Subject);
}
if (clause.pred.StartsWith("?"))
{
tuple.Add(clause.pred, process.Bot.Triples[tripleIndex].Predicate);
}
if (clause.obj.StartsWith("?"))
{
tuple.Add(clause.obj, process.Bot.Triples[tripleIndex].Object);
}
tuples.Add(tuple);
}
}
var nextClause = startIndex + 1;
if (nextClause == this.Clauses.Length)
{
return(tuples);
}
// Recurse into the remaining clauses for each possible tuple.
result = new HashSet <Tuple>();
// TODO: This recursive strategy involving sets has a minor quirk.
// For a query (q: a isA b, notq: b isA x), for subjects a that have more than one predicate isA,
// the results depend on the order in which the triples are defined.
foreach (var tuple in tuples)
{
result.UnionWith(this.SelectFromRemainingClauses(process, tuple, nextClause));
}
return(result);
}
public Uniq(TemplateElementCollection subj, TemplateElementCollection pred, TemplateElementCollection obj)
{
this.Clause = new Clause(subj, pred, obj, true);
}