# Re: What are units-of-measure? e.g., what's a "kilometer"?

```John Cowan wrote:

> > 2. Is kilometer a function? e.g., kilometer(Yangtze) --> 6300
> >    In general: kilometer(physical object) --> number
> >    "The kilometer function maps a physical object to a number."
>
> I think this view is the most nearly correct, but it needs amplification:
> it doesn't capture that it's the *length* (rather than, say, the
> average depth) of the Yangzi that is 6300 km.  So we can rewrite it
> in terms of relations as follows:
>
> Yangzi length X
> X kilometer 6300
>
> where "kilometer" is a relation that maps a length (an abstract property
> of a physical object) into a pure number.

So, kilometer is a function of this sort:

kilometer(length(Yangtze)) --> 6300

"kilometer is a function which maps the length of the Yangtze to 6300."

Another example:

kilometer(avg-depth(Yangtze)) --> 0.25

"kilometer is a function which maps the average depth of the Yangtze to 0.25."

The general case is:

kilometer(distance) --> number

where distance is an abstract dimension object.

How are functions represented syntactically in XML?  Given the above
viewpoint, this form no longer seems appropriate:

<River id="Yangtze">
<length units="kilometer">6300</length>
</River

Perhaps a more faithful representation of:

kilometer(length(Yangtze)) --> 6300

is this:

<River id="Yangtze">
<length>
<kilometer>6300</kilometer>
</length>
</River>

Thoughts?  /Roger

```

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