/// <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 similarity of two synsets
/// </summary>
/// <param name="synset1">First synset</param>
/// <param name="synset2">Second synset</param>
/// <param name="strategy">Strategy to use. All strategies named WuPalmer1994* will produce the same result since only two synsets
/// are available.</param>
/// <param name="relations">Synset relations to follow when computing similarity (pass null for all relations)</param>
/// <returns>Similarity</returns>
public float GetSimilarity(SynSet synset1, SynSet synset2, Strategy strategy, params WordNetEngine.SynSetRelation[] relations)
{
if (relations == null)
{
relations = Enum.GetValues(typeof(WordNetEngine.SynSetRelation)).Cast <WordNetEngine.SynSetRelation>().ToArray();
}
float similarity = 0;
if (strategy.ToString().StartsWith("WuPalmer1994"))
{
// get the LCS along the similarity relations
SynSet lcs = synset1.GetClosestMutuallyReachableSynset(synset2, relations);
if (lcs == null)
{
similarity = 0;
}
else
{
// get depth of synsets
int lcsDepth = lcs.GetDepth(relations) + 1;
int synset1Depth = synset1.GetShortestPathTo(lcs, relations).Count - 1 + lcsDepth;
int synset2Depth = synset2.GetShortestPathTo(lcs, relations).Count - 1 + lcsDepth;
// get similarity
similarity = 2 * lcsDepth / (float)(synset1Depth + synset2Depth);
}
}
else
{
throw new NotImplementedException("Unrecognized strategy");
}
if (similarity < 0 || similarity > 1)
{
throw new Exception("Invalid similarity");
}
return(similarity);
}