the span of time within which data of a given type is available

NOTE For stable long term data, this may be the validity period of the timetable or stop data. For more volatile short term data such as daily operational changes, it may be a shorter operation period such as the day or week. For real-time data this will be the retention period in the system of very volatile data, such as short term movement and prediction data, for example an hour, or as soon as the data is obsolete. Systems that keep historic logs of data value may offer a longer data horizon for some types of volatile data.