prefix_to_url

        High-level api: Convert an identifier from `prefix:tagname` notation to
        `{namespace}tagname` notation. If the identifier does not have a
        prefix, it is assumed that the whole identifier is a tag name.

        Parameters
        ----------

        id : `str`
            Identifier in `prefix:tagname` notation.

        Returns
        -------

        str
            Identifier in `{namespace}tagname` notation.

def prefix_to_url(self, id):
        '''prefix_to_url

        High-level api: Convert an identifier from `prefix:tagname` notation to
        `{namespace}tagname` notation. If the identifier does not have a
        prefix, it is assumed that the whole identifier is a tag name.

        Parameters
        ----------

        id : `str`
            Identifier in `prefix:tagname` notation.

        Returns
        -------

        str
            Identifier in `{namespace}tagname` notation.
        '''

        parts = id.split(':')
        if len(parts) > 1:
            return '{' + self.prefixes[parts[0]] + '}' + parts[1]
        else:
            return '{' + self.url + '}' + id