Extract random walks efficiently

[wouterbeek]

Since it's possible to extract the estimated number of results for an arbitrary triple pattern, we were wondering whether it would also be possible to efficiently retrieve, for a given node X, a random neighbor node Y of X (in constant time).

Looking at the Web Semantics paper from 2013, it seems that this should be doable by querying bitmap triples representation directly.

Thanks in advance!
@airobert and @wouterbeek

[airobert]

@bendiken @MarioAriasGa @rubensworks @RubenVerborgh

[webdata]

This is a first attempt (depends on the "goto" issue #84)

int searchID_subject = mydictionary.stringToId("http://yourinitialNOde", TripleComponentRole.SUBJECT);

TripleID pattern = new TripleID(searchID, 0, 0);
IteratorTripleID it = mytriples.search(pattern);
size_t numResults = it.estimatedNumResults();

int randNumber = 1+int(numResults*rand()/(RAND_MAX + 1.0));

it.goTo(randNumber);

TripleID result=it.next();

[webdata]

Solved with latests commits in develop, 7b92caa

See tool https://github.com/rdfhdt/hdt-cpp/blob/develop/hdt-lib/tests/randomSolution.cpp implementing an example