Answers interleaved:

> Rule: Within a leg, departures occur after arrivals, if there are
> arrivals and departures. I see how to validate that, so long as a
> string compare works. Something like: <xr:validate test="depart >
> arrive" /> I'm not sure how the missing arrival or departure affects
> that.

Your rule is correct except that, unfortunately, XPath does not do string comparison; it tries to convert the values to numbers first. But, there is a workaround. Modify your rule slightly to remove the non-numeric characters as follows (also note that I used the ruleset context to enforce the rule on all legs but the first and last):

  <xr:ruleset context="/schedule/leg[position() &gt; 1 and position() &lt; last()]">

    <xr:validate test="translate(depart,':','') &gt; translate(arrive,':','')" />

  </xr:ruleset>

If the arrival or departure is missing, the rule will fail, which will serve to validate that both nodes exist. If you want a specific error message when a node is missing, you can add a separate rule to validate for this condition.

> Rule: For any leg, the arrival is after the previous leg's departue.

For this use the XPath expression preceding-sibling::leg[1] to get the preceding sibling. Also, note that I changed the ruleset context to enforce the rule on all nodes except the first.

  <xr:ruleset context="/schedule/leg[position() &gt; 1]">

    <xr:validate test="translate(arrive,':','') &gt; translate(preceding-sibling::leg[1]/depart,':','')" />

  </xr:ruleset>

> Rule: For the first leg, there is no arrival.
> Rule: For the last leg, there is no departure.

This one is straight forward:

  <xr:ruleset context="/schedule">

    <xr:validate test="not(leg[1]/arrive)" />

    <xr:validate test="not(leg[last()]/depart)" />

  </xr:ruleset>

> Rule: All legs except first and last have both an arrival and a departure.

This is satisfied by the first ruleset above. However, for an explicit check you can the following to the first ruleset:

    <xr:validate test="boolean(arrive)" />

    <xr:validate test="boolean(depart)" />

> How to do comparisons if the time were expressed in a manner not
> easily compared as strings, e.g. "1/30/2006 08:00"?

Not easy. XPath doesn’t recognize a date/time type. I’d recommend using the standard XML format for dates: 2006-01-30T08:00. This is the ‘standard’ way for dates in XML, and with it you can use the translate() trick to remove the -, T, and : and perform date comparisons.

So, your complete XRules document will look like this:

<xr:rules xmlns:xr="http://www.xrules.org/2003/11">

  <xr:ruleset context="/schedule/leg[position() &gt; 1 and position() &lt; last()]">

    <xr:validate test="translate(depart,':','') &gt; translate(arrive,':','')" />

    <xr:validate test="boolean(arrive)" />

    <xr:validate test="boolean(depart)" />

  </xr:ruleset>

  <xr:ruleset context="/schedule/leg[position() &gt; 1]">

    <xr:validate test="translate(arrive,':','') &gt; translate(preceding-sibling::leg[1]/depart,':','')" />

  </xr:ruleset>

  <xr:ruleset context="/schedule">

    <xr:validate test="not(leg[1]/arrive)" />

    <xr:validate test="not(leg[last()]/depart)" />

  </xr:ruleset>

</xr:rules>

Regards,

Waleed

-----Original Message-----
From: xrules@yahoogroups.com [mailto:xrules@yahoogroups.com] On Behalf Of johnbrockus
Sent: Friday, September 15, 2006 10:14 AM
To: xrules@yahoogroups.com
Subject: [xrules] How to do sibling checks? non-string compares?