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Modeling

(See initial modeling discussion here)

We are basically going to implement the following conversion approach. See at the end for remaining questions.

Unit class

An instance of the Unit class captures one main unit entry in the XML. It may have a primary name (via property hasName) and zero or more aliases (via hasAlias property).

hasDefinition property

This is a functional property to capture the <def> element from the XML description.

hasName property

This is a functional property that indicates the primary name of a given Unit instance. In particular, a unit may not have a primary name.

hasAlias property

Indicates an alternate name for a given Unit instance. A unit can have zero or more aliases associated.

hasSymbol property

Indicates a symbol associated with a given Unit instance. A unit can have zero or more symbols associated.

UnitName class

Instances of the UnitName class capture a name or alias associated with an instance of a class Unit.

namesUnit property

With UnitName as domain, this functional property indicates the Unit instance associated with the name.

hasCardinality property

With UnitName as domain, this functional property indicates whether the name is "singular" or "plural".

Remarks:

• The approach clearly separates the concept of unit from any associated specific names/aliases.
• Those names/aliases will have URIs per se (so they could be self-resolvable)

Example

The following entry from the original vocabulary:

        <unit>
            <def>'/60</def>
            <name><singular>arc_second</singular></name>
            <symbol>"</symbol>
            <symbol>&#x2033;</symbol>           <!-- DOUBLE PRIME -->
            <aliases>
                <name><singular>angular_second</singular></name>
                <name><singular>arcsecond</singular></name>
                <name><singular>arcsec</singular></name>
            </aliases>
        </unit>

will result in the RDF representation:

@prefix :        <http://mmisw.org/ont/mmitest/udunits2-accepted/> .
@prefix prop:    <http://mmisw.org/ont/mmitest/udunits2-prop/> .

:2a1369 
      a                      :Unit ;
      prop:hasDefinition     "'/60" ;
      prop:hasName           "arc_second" ;
      prop:hasAlias          :arcsec, :angular_second, :arcsecond ;
      prop:hasSymbol         "\"", "″" ;

:arc_second
      a                      :UnitName ;
      prop:namesUnit         :2a1369;
      prop:hasCardinality    "singular";

:arcsec
      a                      :UnitName ;
      prop:namesUnit         :2a1369;
      prop:hasCardinality    "singular";

:angular_second
      a                      :UnitName ;
      prop:namesUnit         :2a1369;
      prop:hasCardinality    "singular";

:arcsecond
      a                      :UnitName ;
      prop:namesUnit         :2a1369;
      prop:hasCardinality    "singular";

Questions

Remaining questions to proceed with implementation:

1. Assuming both Unit and UnitName instance URIs will share the same namespace, how to determine the id for each Unit instance in a way that is "stable", that is, that will be preserved even upon multiple conversions as the original vocabularies are updated?

Recommended strategy: Apply an arbitrary but deterministic translation (md5 or sha hash) of the def string, and use the last 6 characters. If a collision results, add '+' to the def string and re-hash; repeat until a unique name results.

• All units must have def strings but a few may not have names.
• Collisions should be rare for the number of units involved. (If worried, use 8 characters.)

Any other questions?

yeah, where did my questions go???

2. How will Units and UnitNames be seen in ORR?

3. How will URLs be generated for the two class types?