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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 get_annotation(component, db_name, db_ref):
 """Construct model Annotations for each component. Annotation formats follow guidelines at http://identifiers.org/. """

    url = get_identifiers_url(db_name, db_ref)
    if not url:
        return None
    subj = component
    ann = Annotation(subj, url, 'is')
    return ann