ANN: Portable Data Component -- time interval (start/end orstart/durati

["Costello, Roger L." <costello@mitre.org>]

Hi Folks,

This is an extension of the start/end portable data component. 

A time interval may be expressed using either of these:

      - start and end values, or
      - start and duration values.

Here are examples using start/duration. 

Example #1

The class starts on May 3, 2011 at 8am and runs for 8 hours:

    <class>
        <start>2011-05-03T08:00:00</start>
        <duration>PT8H</duration>
    </class>

Example #2

My vacation begins June 22, 2011 and is for 3 days:

    <vacation>
        <start>2011-06-22</start>
        <duration>P3D</duration>
    </vacation>

The constraints on the start/end values are those described earlier. 

There is one constraint on the start/duration values: the duration must not be a negative value. 

Determining that duration is not a negative value is not straightforward. One would think that this XPath expression would do the job:

  	xs:duration(duration) gt xs:duration("P0Y")

However, that is not correct. It will generate this error:

    	xs:duration is not an ordered type

Instead, what is required is to treat duration as a string and check that the string starts with the letter 'P' (i.e., not the letter '-'):

	starts-with(duration, 'P')

Here is the time-interval portable data component:

    <xs:complexType name="time-interval">
        <xs:sequence>
            <xs:element name="start">
                <xs:simpleType>
                    <xs:union memberTypes="xs:date xs:time 
                                                                          xs:dateTime" />
                </xs:simpleType>
            </xs:element>
            <xs:choice>
                <xs:element name="end" minOccurs="0">
                    <xs:simpleType>
                        <xs:union memberTypes="xs:date xs:time 
                                                                              xs:dateTime" />
                    </xs:simpleType>
                </xs:element>
                <xs:element name="duration" type="xs:duration" />
            </xs:choice>
        </xs:sequence>
        <xs:assert test="if (exists(end)) then 
                                                if (start castable as xs:dateTime) then
                                                        xs:dateTime(end) gt xs:dateTime(start)
                                               else if (start castable as xs:date) then
                                                       xs:date(end) gt xs:date(start)
                                               else if (start castable as xs:time) then
                                                      xs:time(end) gt xs:time(start)
                                               else true()
                                       else if (exists(duration)) then
                                              starts-with(duration, 'P')
                                      else true()" />
    </xs:complexType>

A summary of all our discussions on Portable Data Components may be found here:

    http://www.xfront.com/xml-schema-1-1/best-practice/portable-data-components/Portable-Data-Components.pdf

/Roger