def process(proc_data):
    """
    Final processing to conform to the schema.

    Parameters:

        proc_data:   (dictionary) raw structured data to process

    Returns:

        List of dictionaries. Structured data with the following schema:

        [
          {
            "user":       string,
            "tty":        string,
            "hostname":   string,
            "login":      string,
            "logout":     string,
            "duration":   string
          }
        ]
    """
    for entry in proc_data:
        if 'tty' in entry and entry['tty'] == '~':
            entry['tty'] = None
        if 'tty' in entry and entry['tty'] == 'system_boot':
            entry['tty'] = 'system boot'
        if 'hostname' in entry and entry['hostname'] == '-':
            entry['hostname'] = None
        if 'logout' in entry and entry['logout'] == 'still_logged_in':
            entry['logout'] = 'still logged in'
    return proc_data
