STMML units and date/time values

[Peter Murray-Rust]

At 15:04 17/10/2002 -0800, Matt Jones wrote:
>Peter,
>
>Thanks for the followup earlier on STMML and its use in our Ecological 
>Metadata Language.  We've run into another issue.  Lots of ecological data 
>include attributes with date, time, or date-time values.  These are 
>obviously numeric expressions of elapsed time on an implied calendar scale 
>(e.g., Gregorian).  How can we define an STMML unit for such an attribute?
>
>Example data
>
>Year      Date         Time       DateTime
>----      ----------   --------   -------------------
>1999      10-10-2002   17:34:45   10-10-2002 17:34:45
>2002      03-04-1943   07:54:00   01-02-2003 08:34:22
>
>Also, how would such a unit relate to the use of an STMML "dataType" of 
>type "xsd:gYear" or "xsd:gDate"?  What is an STMML dataType in relation to 
>the domain of an attribute and its precision?
Excellent question! I haven't actually hacked this in software so this is a 
first pass... There are two separate approaches for time.

STMML allows users to define scalar dataTypes to which they can attach 
scientific units.  The scientific units are based on the SI system. We are 
working closely with NIST  and CODATA in this area and will adopt their 
approach whenever it is formalized. So for simple chemists who measure 
things in "seconds" or "days" it is straightforward. Example:

<scalar dictRef="mydict:halflife" units="units:year" title="plutonium 
halflife">25000</scalar>

would be OK.

** We already have a demo application of conversion between units using XSL 
which we can send to you along with our growing dictionary. ***

The W3C deliberately did not introduce units into Schemas. IMO this was a 
pity, but... However they did introduce dataTypes, and for Time - based on 
ISO8601 - this implies units.

http://www.w3.org/TR/NOTE-datetime
expounded in
http://www.cl.cam.ac.uk/~mgk25/iso-time.html

So you could also define your own scalar by:

<scalar dataType="xsd:gYear" title="moon landing">1969</scala>

You could then validate it using W3 Schema tools.

I think Time is the only W3C data type with implied units.

The advantage of this is it is standard. But you would have to write your 
own software (probably) to do conversions. XML is also closely related to 
Java and it is almost certain that Java tools will convert reliably from 
ISO8601. But the actual implementation is hard to navigate through.

>For example, if I specify that an attribute "X" measured on an "interval" 
>scale has a domain with a minimum value of 0 and a maximum value of 10 in 
>units of "meter" with a precision of "0.5 meter" then I know pretty much 
>everything I need to analyze it.  Can you map the STMML terminology (e.g. 
>dataType, unit) onto this example?  That would be extremely useful to me.

<scalar title="The universal X" dictRef="mydict:x123" min="3.22" max="4.22" 
errorBasis="range" units="unitdict:met01" 
dataType="nonNegativeNumber" >3.72</scalar>

Will record the data but only the lower constraints. We would define the 
constraints either in a dictionary or a schema (we hope to use the 
dictionary as the primary definition because schemas are so horrible).

In a schema you would have to write something like:

<xsd:simpleType name="xValueType" id="st.xValueType">
   <xsd:annotation>
     <xsd:documentation>
       <div class="description">An X Type</div>
     </xsd:documentation>
   </xsd:annotation>
   <xsd:restriction base="xsd:decimal">
     <xsd:minInclusive value="0.0"/>
     <xsd:maxInclusive value="10.0"/>
   </xsd:restriction>
</xsd:simpleType>


This is horrible to most sentient humans (Henry and I spend our evening 
hacking this sort of stuff) so we want to put it in the dictionaries. The 
initial design of dictionaries didn't cater for data types so we want to 
develop something like:
In a dictionary we might expect:

<entry id="xxx">
   ...An X object ...
   <dataType extends="xsd:decimal" min="0" max="10" />

and then autogenerate the stuff above. It's high priority but not yet 
hacked. I will send you a copy of our latest demo - I won't post it here 
because the list is copied in and we haven't yet published it...

If this makes sense and you have units you can add to the dictionary that 
would be exciting :-) We hope to post this on sourceforge shortly...


P.


>Thanks for the help,
>Matt
>
>--
>*******************************************************************
>Matt Jones                                    jones at nceas.ucsb.edu
>http://www.nceas.ucsb.edu/    Fax: 425-920-2439   Ph: 907-789-0496
>National Center for Ecological Analysis and Synthesis (NCEAS)
>
>Interested in ecological informatics? http://www.ecoinformatics.org
>*******************************************************************