/**
* Checks if the specified piece of evidence is relevant for the supplied trustor. More
* specifically, a piece of evidence is relevant for indirect trust evaluation if:
*
* <ol>
* <li>type == {@link TrustEvidenceType#DIRECTLY_TRUSTED DIRECTLY_TRUSTED}
* <li>trustorId != evidence.subjectId, i.e. ignore trust opinions originating <i>from</i> the
* trustor
* <li>trustorId != evidence.objectId, i.e. ignore trust opinions <i>about</i> the trustor
* <li>evidence.subjectId != evidence.objectId, i.e. ignore self-referencing trust opinions
* </ol>
*
* @param trustorId
* @param evidence
* @return <code>true</code> if the specified piece of evidence is relevant for the supplied
* trustor; <code>false</code> otherwise.
*/
private boolean areRelevant(final TrustedEntityId trustorId, final ITrustEvidence evidence) {
boolean result = false;
if (TrustEvidenceType.DIRECTLY_TRUSTED == evidence.getType()
&& !trustorId.equals(evidence.getSubjectId())
&& !trustorId.equals(evidence.getObjectId())
&& !evidence.getSubjectId().equals(evidence.getObjectId())) {
result = true;
}
LOG.debug(
"areRelevant: trustorId={}, evidence={}, result={}",
new Object[] {trustorId, evidence, result});
return result;
}
private static Set<TrustEvidence> iEvidenceToEvidence(Set<ITrustEvidence> evidenceSet) {
final Set<TrustEvidence> result = new LinkedHashSet<TrustEvidence>(evidenceSet.size());
for (final ITrustEvidence evidence : evidenceSet) {
result.add(
new TrustEvidence(
evidence.getSubjectId(),
evidence.getObjectId(),
evidence.getType(),
evidence.getTimestamp(),
evidence.getInfo(),
evidence.getSourceId()));
}
return result;
}
/*
* @see org.societies.privacytrust.trust.api.engine.IIndirectTrustEngine#evaluate(org.societies.api.privacytrust.trust.model.TrustedEntityId, org.societies.privacytrust.trust.api.evidence.model.ITrustEvidence)
*/
@Override
public Set<ITrustedEntity> evaluate(
final TrustedEntityId trustorId, final ITrustEvidence evidence) throws TrustEngineException {
if (trustorId == null) {
throw new NullPointerException("trustorId can't be null");
}
if (evidence == null) {
throw new NullPointerException("evidence can't be null");
}
LOG.debug("evaluate: trustorId={}, evidence={}", trustorId, evidence);
final Set<ITrustedEntity> resultSet = new HashSet<ITrustedEntity>();
if (!this.areRelevant(trustorId, evidence)) {
return resultSet;
}
try {
// Does similarity between trustor and subject needs re-evaluation?
boolean doSimilarityEval = false;
// Create the trusted entity the evidence object refers to if not already available
ITrustedEntity trustee =
(ITrustedEntity) this.trustRepo.retrieveEntity(trustorId, evidence.getObjectId());
if (trustee == null) {
trustee = super.trustRepo.createEntity(trustorId, evidence.getObjectId());
} else {
doSimilarityEval = true;
}
LOG.debug("evaluate: doSimilarity={}", doSimilarityEval);
resultSet.add(trustee);
switch (evidence.getType()) {
// Update value
case DIRECTLY_TRUSTED:
// Check if similarity between trustor and subject needs re-evaluation
if (doSimilarityEval
&& TrustedEntityType.CSS == evidence.getSubjectId().getEntityType()) {
final ITrustedCss subject =
(ITrustedCss) super.createEntityIfAbsent(trustorId, evidence.getSubjectId());
final Double similarity =
this.trustSimilarityEvaluator.evaluateCosineSimilarity(
trustorId, evidence.getSubjectId());
LOG.debug("evaluate: similarity={}", similarity);
if (similarity != null && !Double.isNaN(similarity)) {
subject.setSimilarity(similarity);
super.trustRepo.updateEntity(subject);
}
}
// Fetch top N users
final Map<TrustedEntityId, ITrustedCss> topNCssMap = this.retrieveTopNCss(trustorId);
LOG.debug("evaluate: topNCssMap={}", topNCssMap);
double weightedOpinionSum = 0d;
double weightSum = 0d;
// Retrieve all Indirect Trust Evidence related to the object
// referenced in the specified TrustEvidence
final Set<ITrustEvidence> evidenceSet =
super.trustEvidenceRepo.retrieveLatestEvidence(
null, evidence.getObjectId(), evidence.getType(), null);
LOG.debug("evaluate: evidenceSet={}", evidenceSet);
for (final ITrustEvidence relatedEvidence : evidenceSet) {
if (!(relatedEvidence.getInfo() instanceof Double)) {
LOG.warn("Related evidence " + relatedEvidence + " has no trust value!");
continue;
}
final ITrustedCss opinionSource = topNCssMap.get(relatedEvidence.getSubjectId());
if (opinionSource == null) {
LOG.warn(
"Could not find CSS trust relationship with related evidence subject '"
+ relatedEvidence.getSubjectId()
+ "'");
continue;
}
final Double weight = evaluateWeight(opinionSource);
Double weightedOpinion = null;
if (weight != null) {
final double meanOpinion =
this.retrieveMeanTrustOpinion(relatedEvidence.getSubjectId());
weightedOpinion = weight * ((Double) relatedEvidence.getInfo() - meanOpinion);
LOG.debug(
"evaluate: subjectId={}, meanOpinion={}, weightedOpinion={}",
new Object[] {relatedEvidence.getSubjectId(), meanOpinion, weightedOpinion});
}
if (weightedOpinion == null) {
LOG.warn(
"Ignoring related evidence " + relatedEvidence + ": Weighted opinion is null");
continue;
}
weightedOpinionSum += weightedOpinion;
weightSum += Math.abs(weight);
}
LOG.debug("evaluate: weightedOpinionSum={}, weightSum={}", weightedOpinionSum, weightSum);
// t_x,i = avg(t_x) + weighted opinions
double value =
super.trustRepo.retrieveMeanTrustValue(trustorId, TrustValueType.DIRECT, null);
final double confidence;
if (weightSum > 0) {
value += weightedOpinionSum / weightSum;
confidence = 0.5d; // TODO constant or what?
} else {
confidence = 0.25d; // TODO constant or what?
}
LOG.debug("evaluate: value={}", value);
if (value > 1) {
value = 1.0d; // TODO use constant
} else if (value < 0) {
value = 0.0d; // TODO use constant
}
trustee.getIndirectTrust().setValue(value);
trustee.getIndirectTrust().setConfidence(confidence);
break;
default:
throw new TrustEngineException("Unsupported type: " + evidence.getType());
}
// Add related evidence to trustee
trustee.addEvidence(evidence);
// Persist updated TrustedEntities in the Trust Repository
for (final ITrustedEntity entity : resultSet) {
super.trustRepo.updateEntity(entity);
}
} catch (Exception e) {
throw new TrustEngineException(
"Could not evaluate indirect trust evidence " + evidence + ": " + e.getLocalizedMessage(),
e);
}
return resultSet;
}