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[Bug 13465] Implement datatyping in Microdata

From: <bugzilla@jessica.w3.org>
Date: Tue, 09 Aug 2011 00:08:14 +0000
To: public-html-bugzilla@w3.org
Message-Id: <E1QqZri-0002uB-3H@jessica.w3.org>
http://www.w3.org/Bugs/Public/show_bug.cgi?id=13465

Manu Sporny <msporny@digitalbazaar.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|NEEDSINFO                   |

--- Comment #4 from Manu Sporny <msporny@digitalbazaar.com> 2011-08-09 00:08:12 UTC ---
"If the property is given using a URL property element the type is implicitly a
URL. Is that enough?"

How does this happen? Is it machine readable? You are sort-of talking about
type coercion here:

http://json-ld.org/spec/ED/20110808#type-coercion

Type coercion is just one aspect of this issue. Yes, adding type coercion to
microdata would go toward addressing this issue. However, you can't always
depend on type coercion - for example, when a vocabulary is used to specify
multiple different types of units. For example - "weight" can be defined in a
variety of different units of measurement.

"If one doesn't understand the item's vocabulary itself, why would one be
inspecting individual property values?"

That's not the issue. The question should be "If a vocabulary term can express
something like 'weight', what is the best way to associate the unit of
measurement with the number?"

"In what circumstances would a microdata consumer be able to make use of data
type information, without any hardwired information about the vocabulary?"

Not "microdata consumer" - "data consumer". You can have a software module that
is capable of translating weights and measures into any unit that you want. You
can include this software module in your software to do the translation
accurately. For example - I have an application that works with recipes, one of
the ways to declare an ingredient in a recipe is by weight. You have two major
schools of thought on expressing weights - imperial and metric. There are
hundreds of millions of people that use both, so asking people to use one or
the other exclusively unnecessarily excludes hundreds of millions of people.
So, you can't:

 * Tell people to just use metric measurements
 * Create a library that is capable of reading any type of short-hand for
weights/measurements because of overlaps in short-hand for expressing
weights/measures (m for minutes vs. metres, deg for degrees (angle) vs. degrees
(temperature)).

However, if you tag it with an IRI datatype, the datatype is unique and
discoverable (you can provide other things like the name of the datatype in
multiple different languages). A consuming application wouldn't have to know
anything about the vocabulary to know that a datatype of
http://example.org/measurement/temperature#fahrenheit is a measurement for
temperature in degrees fahrenheit as well as how to express the value in a
person's native language because dereferencing the IRI will provide a fair
amount of other information about the measurement (like the language-native
glyphs for the concept).

"If it does have hardwired information about the vocabulary, why does data
typing need to be part of the general syntax instead of the vocabulary-specific
semantics?"

You shouldn't hardwire this type of information in the vocabulary. See the use
case above.

"I looked at the use-cases that microdata was written to cover and didn't see
any where it would be useful."

Then add the recipe use case to Microdata. Being able to specify units of
measurement is important when baking a cake, giving somebody a dose of
medication, and when sending scientific instruments to Mars.

"Why can't the vocabulary require that a particular type always be used,
possibly a type that includes units in-band and therefore can accommodate
different units without extra metadata (e.g. "5km", "5mi", "5m")?"

I answer this above. Doing this is a hack that requires people to express their
units of measurement in a specific way. People are not very good at doing this.

"What's a concrete example where this would be useful, as opposed to hardwiring
the units into the vocabulary?"

See above.

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Received on Tuesday, 9 August 2011 00:08:19 UTC

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