[seek-dev] What to do about "nil"

Bertram Ludaescher ludaesch at sdsc.edu
Tue Nov 9 11:18:30 PST 2004

What about the more fundamental question? How do you represent 'nil'
in the Ptolemy and/or Java type system? I would hope that one could in
fact have such a distinguished value... and that the XML Schema ->
Ptolemy (or Java) type translation in fact create the correct
representation.. Handling of that value in the workflow would than be
quite clean, as supposed to an ad-hoc solution.
(But then again... the world itself seems quite ad-hoc ;-)


>>>>> "MJ" == Matt Jones <jones at nceas.ucsb.edu> writes:
MJ> Hi Rod,
MJ> You're right that the data needs to be preserved even when the lat/lon 
MJ> values are nil -- some people may want to see the rest of the Darwin 
MJ> Core record for various workflows.  However, for the purposes of the 
MJ> niche model example, I think we want to filter out all records that lack 
MJ> lat/lon data.  So.... maybe the best solution is to fire some sort of 
MJ> null or missing value code on the lat/lon ports, and then provide a 
MJ> filter downstream in the workflow that only keeps records that have 
MJ> legit lat/lon values -- this is what GARP ultimately needs and what 
MJ> should be saved in the file.
MJ> Matt
MJ> Rod Spears wrote:
>> Here is the schema for Latitude per the DarwinCore spec:
>> <xsd:element name="DecimalLatitude" 
>> substitutionGroup="digir:searchableReturnableData" nillable="true">
>> <xsd:annotation>
>> <xsd:documentation>The latitude of the location from which 
>> the cataloged item was collected, expressed in decimal 
>> degrees.</xsd:documentation>
>> </xsd:annotation>
>> <xsd:simpleType>
>> <xsd:restriction base="xsd:decimal">
>> <xsd:minInclusive value="-90.0"/>
>> <xsd:maxInclusive value="90.0"/>
>> </xsd:restriction>
>> </xsd:simpleType>
>> </xsd:element>
>> Note that the value can be "nil" and it also has a restriction. When the 
>> value reaches the DarwinCoreDataSource as a string it is either a valid 
>> number within the range or an empty string (length zero).
>> Currently, I convert the empty string to "0.0" which is the wrong thing 
>> to do. The question is what should I do? As Dan suggested I could pick 
>> an arbitray large number and pass that back, but that assumes the 
>> consumer will know what to do with that value. I could skip any and all 
>> rows that have empty Lat or Long values, but that may be bad for 
>> consumers that want to see that data but don't care if it is nil (empty) 
>> or not.
>> Any thoughts?
>> Rod
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MJ> -- 
MJ> -------------------------------------------------------------------
MJ> Matt Jones                                     jones at nceas.ucsb.edu
MJ> http://www.nceas.ucsb.edu/    Fax: 425-920-2439    Ph: 907-789-0496
MJ> National Center for Ecological Analysis and Synthesis (NCEAS)
MJ> University of California Santa Barbara
MJ> Interested in ecological informatics? http://www.ecoinformatics.org
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