An id is an label attribute with a numeric representation that identify uniquely an entity or a relationship in a local scope.
versus the name attribute which is the textual counterpart representation
If the id attribute is chosen as the local identifier, it will be:
If there is no namespace functionality that describe the identifier, the id of an entity describe its identity. <MATH> \Large id+entity = identity </MATH>
See How to protect numerical Id ? (obfuscate, id encryption)