Around with PHP to parse large XML files, do you want to use a SAX parser, the XML reads files from top to bottom and not transforming into an object. This is the XMLReader PHP.

An example:

$data = new Data();
$reader = new \XMLReader();
$reader->open($file);

while ($reader->read()) {
    if ($reader->nodeType == \XMLReader::ELEMENT) {
        switch ($reader->name) {
            case "tagName1" :
                $node = new \SimpleXMLElement($reader->readOuterXML());
                $attributes = $node->attributes();
                $entity = new Entity();
                $entity->setId($attributes['id']);
                $entity->setName($attributes['name']);
                $entity->setCode($attributes['code']);
                $data->addEntity($entity);

                break;

            case  "tagName2":
                $node = new \SimpleXMLElement($reader->readOuterXML());
                $attributes = $node->attributes();
                $entity = new OtherEntity();
                $entity->setId($attributes['id']);
                $entity->setName($attributes['name']);
                $entity->setCode($attributes['code']);
                $data->addOtherEntity($entity);

                break;
        }
    }
}