/**
* Generate a hash value to simplify the comparison of this data
* container with other containers. Subdata is taken into account.
*
* The hash uses PHP's md5 implementation, which is among the fastest
* hash algorithms that PHP offers.
*
* @note This function may be used to obtain keys for SemanticData
* objects or to do simple equalitiy tests. Equal hashes with very
* high probability indicate equal data. However, the hash is
* sensitive to the order of properties and values, so it does not
* yield a reliable way to detect inequality: objects with different
* hashes may still contain the same data, added in different order.
*
* @return string
*/
public function getHash()
{
$stringToHash = '';
// here and below, use "_#_" to separate values; really not much care needed here
$stringToHash .= '_#_' . $this->mSubject->getSerialization();
foreach ($this->getProperties() as $property) {
$stringToHash .= '_#_' . $property->getKey() . '##';
foreach ($this->getPropertyValues($property) as $di) {
$stringToHash .= '_#_' . $di->getSerialization();
}
$stringToHash = md5($stringToHash);
// intermediate hashing to safe memory
}
foreach ($this->getSubSemanticData() as $data) {
$stringToHash .= '#' . $data->getHash();
}
return md5($stringToHash);
}
/**
* Generate a hash value to simplify the comparison of this data
* container with other containers. Subdata is taken into account.
*
* The hash uses PHP's md5 implementation, which is among the fastest
* hash algorithms that PHP offers.
*
* @note This function may be used to obtain keys for SemanticData
* objects or to do simple equality tests. Equal hashes with very
* high probability indicate equal data.
*
* @return string
*/
public function getHash()
{
if ($this->hash !== null) {
return $this->hash;
}
$hash = array();
$hash[] = $this->mSubject->getSerialization();
foreach ($this->getProperties() as $property) {
$hash[] = $property->getKey();
foreach ($this->getPropertyValues($property) as $di) {
$hash[] = $di->getSerialization();
}
}
foreach ($this->getSubSemanticData() as $data) {
$hash[] = $data->getHash();
}
sort($hash);
$this->hash = md5(implode('#', $hash));
unset($hash);
return $this->hash;
}
