/// <summary>
/// Gets the closest synset that is reachable from the current and another synset along the given relations. For example,
/// given two synsets and the Hypernym relation, this will return the lowest synset that is a hypernym of both synsets. If
/// the hypernym hierarchy forms a tree, this will be the lowest common ancestor.
/// </summary>
/// <param name="synset">Other synset</param>
/// <param name="relations">Relations to follow</param>
/// <returns>Closest mutually reachable synset</returns>
public SynSet GetClosestMutuallyReachableSynset(SynSet synset, IEnumerable <WordNetEngine.SynSetRelation> relations)
{
// avoid cycles
Set <SynSet> synsetsEncountered = new Set <SynSet>();
synsetsEncountered.Add(this);
// start search queue
Queue <SynSet> searchQueue = new Queue <SynSet>();
searchQueue.Enqueue(this);
// run search
SynSet closest = null;
while (searchQueue.Count > 0 && closest == null)
{
SynSet currSynSet = searchQueue.Dequeue();
/* check for a path between the given synset and the current one. if such a path exists, the current
* synset is the closest mutually reachable synset. */
if (synset.GetShortestPathTo(currSynSet, relations) != null)
{
closest = currSynSet;
}
// otherwise, expand the search along the given relations
else
{
foreach (SynSet relatedSynset in currSynSet.GetRelatedSynSets(relations, false))
{
if (!synsetsEncountered.Contains(relatedSynset))
{
searchQueue.Enqueue(relatedSynset);
synsetsEncountered.Add(relatedSynset);
}
}
}
}
return(closest);
}
/// <summary>
/// Gets the shortest path from the current synset to another, following the given synset relations.
/// </summary>
/// <param name="destination">Destination synset</param>
/// <param name="relations">Relations to follow, or null for all relations.</param>
/// <returns>Synset path, or null if none exists.</returns>
public List <SynSet> GetShortestPathTo(SynSet destination, IEnumerable <WordNetEngine.SynSetRelation> relations)
{
if (relations == null)
{
relations = Enum.GetValues(typeof(WordNetEngine.SynSetRelation)) as WordNetEngine.SynSetRelation[];
}
// make sure the backpointer on the current synset is null - can't predict what other functions might do
_searchBackPointer = null;
// avoid cycles
Set <SynSet> synsetsEncountered = new Set <SynSet>();
synsetsEncountered.Add(this);
// start search queue
Queue <SynSet> searchQueue = new Queue <SynSet>();
searchQueue.Enqueue(this);
// run search
List <SynSet> path = null;
while (searchQueue.Count > 0 && path == null)
{
SynSet currSynSet = searchQueue.Dequeue();
// see if we've finished the search
if (currSynSet == destination)
{
// gather synsets along path
path = new List <SynSet>();
while (currSynSet != null)
{
path.Add(currSynSet);
currSynSet = currSynSet.SearchBackPointer;
}
// reverse for the correct order
path.Reverse();
}
// expand the search one level
else
{
foreach (SynSet synset in currSynSet.GetRelatedSynSets(relations, false))
{
if (!synsetsEncountered.Contains(synset))
{
synset.SearchBackPointer = currSynSet;
searchQueue.Enqueue(synset);
synsetsEncountered.Add(synset);
}
}
}
}
// null-out all search backpointers
foreach (SynSet synset in synsetsEncountered)
{
synset.SearchBackPointer = null;
}
return(path);
}
