Re: [Fenfire-dev] RDF traversal utility methods

[Tuomas Lukka]

On Sun, Aug 17, 2003 at 04:17:38PM +0300, Tuukka Hastrup wrote:
> On Sun, 17 Aug 2003, Tuomas Lukka wrote:
> > On Sat, Aug 16, 2003 at 02:19:07PM +0300, Tuukka Hastrup wrote:
> > > Now I see - adding findN_AAX_Iter would require ind_210? 
> > 
> > or 120. Either one can be used. Hmm, we have that so it wouldn't hurt
> > to put it there.
> 
> Great.
> 
> > Actually, for this purpose, how about 
> > 
> >     swamp.util.Iteration.iterateAllNodes(ConstGraph g)
> > 
> > for getting all nodes?
> 
> Wouldn't it make sense to have it in ConstGraph interface? And it could
> have iterateAllSubjects and iterateAllObjects as well, and iterateAllNodes
> would just combine them.

No, that's not true - there are also predicates.
And we want each node only once.

Iterating all subjects *is* there.

But yes, we could have ConstGraph.findN_Nodes_Iter() if you like.

> > > In Traversals, I should rather modify findComponents to get 
> > > the initial node set as an iterator, so the caller can limit it to its 
> > > needs.
> > 
> > Why get a *set* as an *iterator*? 
> 
> Because it's probably generated with findN_X11_Iter, and the method uses
> it to iterate the nodes.

Hmm.

> > This is a place where swamp is not doing the accepted
> > java Collection framework thing: one of the design rules there was
> > 
> >     **Iterators should not be used as pseudo-sets**
> 
> Do they have a rationale? Yes, if you use an iterator, you could build a 
> set first and then iterate that. 

That you can't e.g. check if something is in an iterator you're given.
It's too narrow an interface.

> > So I'm thinking: to do better in that way, we should maybe have
> > findN_AAX_Set which returns a set of nodes.
> 
> Do you mean for all findN methods, or these as a special case?

All.

> > However, efficiency may be a problem there :(
> 
> In addition to general overhead, at least concatenating two iterators is 
> simple, but set union I'd imagine is not.

Both are O(N).

> > > By the way, a concatenating iterator similar to the one in Traversals 
> > > would be useful in other places as well. At least it allowed me to 
> > > simplify using non-directed properties, combining iterations of 11X and 
> > > X11 into one.
> > 
> > See above... 
> 
> So if you have a non-directed RDF property, your code needs to check both 
> directions (11X and X11). That is seldom clean in Java (no "for each" 
> statements). So I made an iterator that simply combines results from 11X 
> and X11, and use that in my code. Further, we have other code dealing with
> non-directed properties, and they could be cleaner with the same 
> technique.

Problem: you may get the same node twice.
)
        Tuomas