def get_edge(source, target, interaction):
    """
    Get the edge information in JSON format.

    :param source: the id or name of source node.
    :param target: the id or name of target node.
    :param interaction: the interaction of edge.

    :return : the JSON value about edge.
    """
    if interaction is None:
        itr = '-'
    else:
        itr = interaction

    edge = {
        'data': {
            'source': source,
            'target': target,
            'interaction': itr
        }
    }

    return edge