A Timing schedule can be a list of events and/or criteria for when the event happens, which can be expressed in a structured form and/or as a code. When both event and a repeating specification are provided, the list of events should be understood as an interpretation of the information in the repeat structure. The Timing data type allows modifier extensions.
If the timing schedule has repeating criteria, the repeat can occur a given number of times per the specified duration or in relation to some repeating real-world event. If no end condition is specified, the schedule will terminate on some criteria that are expressed elsewhere. Many systems avoid the complexity of the Timing structure by using a text field for timing instructions. This maps to Timing.code.text.
Note, though, that some systems include timing details in something like ‘Dosage instructions’ which is wider than just Timing; those systems do not use the Timing data type. Other systems use a set of ‘common’ codes – including, but usually not limited to, widely understood acronyms such as “bis in die (BID)” which means in Latin, twice a day. If a Timing.code is provided, the code is understood to be a complete statement of whatever is specified in the structured timing data (except for Timing.repeat.bounds, which applies to the code), and either the code or the data may be used to interpret the Timing. A structured timing specification should be provided whenever possible, unless the code is BID, ter in die (TID) which in Latin means three times a day, quater in die (QID) which in Latin means four times a day, ante meridiem (AM) which in Latin means Before Midday or Post Meridiem (PM) which in Latin means After Midday, which have a ubiquitous meaning.
These codes shall be understood as having the formal meanings. Note that BID, etc. are defined as ‘at institutionally specified times’. For example, an institution may choose that BID is “always at 7am and 6pm”. If it is inappropriate for this choice to be made, the code BID should not be used. Instead, a distinct organization-specific code should be used in place of the HL7-defined BID code and/or a structured representation should be used (in this case, timeOfDay).
Timing is used in the following places: