def reference_products_as_string(dataset):
    """Get all reference products as a string separated by ``'|'``.

    Return ``'None found'`` if no reference products were found."""
    exchanges = sorted([exc['name']
                        for exc in dataset['exchanges']
                        if exc['type'] == 'reference product'])
    if not exchanges:
        return "None found"
    else:
        return "|".join(exchanges)