clarify what today() and now() return exactly

[MartijnR]

@lognaturel writes:

Would be good to explicitly call out the format and/or say it's DateUtils.roundDate(new Date()), same with now()...

It should be clear what should be returned by these functions at least for datatypes: date, time, datetime, integer, decimal (and string? - that one scares me).

This should be done in a language-agnostic manner (no references to Java or JavaRosa).

[lognaturel]

Oops, yes, you're right about it needing to be language-agnostic.

[lognaturel]

XForms equivalents are local-date() and now(), both return strings. But I agree that's not as useful. Were you thinking it could be written as something like "a date object as defined by the implementation language's standard libraries"?

[MartijnR]

Oh totally didn't realize that it is in XForms.

Your "date object" suggestion makes sense to me. I think XPath has no way of calculating today() + 1 correctly, because it cannot recognize datetime strings as special strings.

So maybe we need to describe in the spec how a datetime string is converted to a "Number" and "String" type (in XPath terminology) internally in the XPath evaluator, so independent from the datatype of the question.

[lognaturel]

Err, right. XPath. So today() and now() are intended to be custom XPath functions rather than XForms functions. Given their usage, I guess that makes sense. The relationship between XPath and XForms is also something that might merit a sentence or two.

XPath does define a format for date and time. I didn't totally understand what you said about today() + 1. Xpath defines the add-dayTimeDuration-to-dateTime) function for that behavior which backs + for a duration and a dateTime. Do you mean that in the context of this sub-spec, the date-time and duration types aren't defined which is why that can't be supported?

[MartijnR]

(I'm just thinking out loud, this date/datetime stuff is very confusing to me).

I meant that an XPath 1.0 evaluator doesn't have a built-in date-like type (it only has Number, String, Nodeset and Boolean, and converts string values to one of these depending on the type of function/operator). So if you're sending an expression such as "now() + 1", which I think we support in ODK, to a pure XPath 1.0 evaluator, with XForms 1.0 now() support, you'd get response NaN. Note: the actual datatype (in <bind> of the question this expression belongs to is not relevant.

So I wonder if we could write in our spec:

• now() as in XForms 1.0
• today() as now() but without the 'T' and time component.

[And the real ODK customization:]

In addition, it is possible in ODK XForms to perform arithmetic and comparisons with date and datetime strings whereby each is converted to [rounded? tbc] days since the epoch (1970-01-01T00:00:00Z).

Would that correspond to how JavaRosa does things, or have I misunderstood?

Maybe a more realistic example would be the expression ". < today()", where the XPath evaluator has to recognize that "." is a date or datetime. This is a custom thing we do.

P.S. in hindsight, I think we should have obligated users to wrap dates in date() for comparisons and arithmetic.

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