public function determineEntityType($entity)
    {
        // remove braces at the beginning (only if $entity looks like <http://...>)
        if ('<' == substr($entity, 0, 1)) {
            $entity = str_replace(['>', '<'], '', $entity);
        }

        // checks if $entity is an URL
        if (true === $this->rdfHelpers->simpleCheckURI($entity)) {
            return 'uri';

        // checks if ^^< is in $entity OR if $entity is surrounded by quotation marks
        } elseif (false !== strpos($entity, '"^^<')
            || ('"' == substr($entity, 0, 1) && '"' == substr($entity, strlen($entity) - 1, 1))) {
            return 'typed-literal';

        // blank node
        } elseif (false !== strpos($entity, '_:')) {
            return 'blanknode';

        // checks if $entity is an URL, which was written with prefix, such as rdfs:label
        } elseif (false !== strpos($entity, ':')) {
            return 'uri';

        // checks if "@ is in $entity
        } elseif (false !== strpos($entity, '"@')) {
            return 'literal';

        // checks if $entity is a string; only strings can be a variable
        } elseif (true === is_string($entity)) {
            return 'var';

        // unknown type
        } else {
            return null;
        }
    }