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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def classify_identifier(did):
 """Return a text fragment classifying the ``did`` Return <UNKNOWN> if the DID could not be classified. This should not normally happen and may indicate that the DID was orphaned in the database. """

    if _is_unused_did(did):
        return 'unused on this Member Node'
    elif is_sid(did):
        return 'a Series ID (SID) of a revision chain'
    elif is_local_replica(did):
        return 'a Persistent ID (PID) of a local replica'
    elif is_unprocessed_local_replica(did):
        return (
            'a Persistent ID (PID) of an accepted but not yet processed local replica'
        )
    elif is_archived(did):
        return 'a Persistent ID (PID) of a previously archived local object'
    elif is_obsoleted(did):
        return 'a Persistent ID (PID) of a previously updated (obsoleted) local object'
    elif is_resource_map_db(did):
        return 'a Persistent ID (PID) of a local resource map'
    elif is_existing_object(did):
        return 'a Persistent ID (PID) of an existing local object'
    elif is_revision_chain_placeholder(did):
        return (
            'a Persistent ID (PID) of a remote or non-existing revision of a local '
            'replica'
        )
    elif is_resource_map_member(did):
        return (
            'a Persistent ID (PID) of a remote or non-existing object aggregated in '
            'a local Resource Map'
        )
    logger.warning('Unable to classify known identifier. did="{}"'.format(did))
    return '<UNKNOWN>'