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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 Reference(uri, meaning=None):
 """ Represents external information, typically original obs data and metadata. Args: uri(str):
 Uniform resource identifier for external data, e.g. FITS file. meaning(str):
 The nature of the document referenced, e.g. what instrument and filter was used to create the data? """

    attrib = {'uri': uri}
    if meaning is not None:
        attrib['meaning'] = meaning
    return objectify.Element('Reference', attrib)