An interesting post recently showed up at the Pinnacle21 forum regarding validation of ISO-8601 durations. For those not familiar with ISO-8601 durations, this is about expressing time spans ("durations") in a machine-readable format. For example, a duration of 1 week is expressed as "P1W", a duration of 1 month and 21 days as "P1M21D". You can even have more complicated durations such as "3 days and 5 milliseconds" which is expressed as "P3DT0.005S".
The discussion was about rule FDAN039 (a SEND rule), which states "Value of Duration, Elapsed Time, and Interval variables (--DUR, --ELTM, --EVLINT) must conform to the ISO 8601 international standard". This rule is a consequence of section 126.96.36.199 "Intervals of Time and Use of Duration for --DUR Variables" in the SDTM-IG and section 4.4.3 "Intervals of Time and Use of Duration for --DUR Variables" in the SEND-IG.
First remark that the rule as formulated by the FDA (was it?) is not 100% correctly defined, as it suggests that the valid ISO-8601 value "2017-07-01" is a valid value for e.g. "CLELTM", which it isn't. Rules should be exact!
The discussion on the Pinnacle21 forum was about the regular expression to validate this rule. Here is a snapshot:
Got it? Understood it?
I am not going to show you the alternative the forum contributor proposed as it is as unreadable as the one above ...
So, how would the rule implementation look like if we were (finally) allowed to submit data in XML? In that case, we could easily use XQuery, and make the rule implementation independent of the software used. Such rule implementations are already public available for all SDTM, SEND and most ADaM validation rules published by CDISC, FDA and PMDA.
Here is the core of the rule FDAN039 expressed in XQuery:
An error is then returned when the value is not a valid schema duration and not a valid "week" duration:
Time to move away from SAS Transport 5 and to move to a modern format like XML ... It would make validation so much easier ...
Your comments are welcome as always!