def is_start_chunk(prev_tag, cur_tag):
    """Check if an entity started between the previous and current tags.

    Parameters
    ----------
    prev_tag: str
        Previous chunk tag.

    cur_tag: str
        Current chunk tag.

    Returns
    -------
    chunk_start: boolean.
        True if current tag is the started part of a entity, otherwise False.

    """
    if cur_tag == 'O':
        return False
    if prev_tag == 'O':
        return True
    cur_tag_pos, cur_tag_name = cur_tag.split('-')
    prev_tag_pos, prev_tag_name = prev_tag.split('-')
    if cur_tag_pos in ['B', 'S'
        ] or cur_tag_name != prev_tag_name or prev_tag_pos in ['E', 'S']:
        return True
    return False
