machine-data

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(As supplementary data in an empty abbr element: Removed example as testing revealed empty ABBR still exposed to screen readers. No benefit to use (abuse).)
(Cases of Fixed Data Formats in Microformats: moved hReview rating example to a section on misconceptions)
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===hReview===
===hReview===
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* Uses an ISO 8601 date-time for <code>dtreviewed</code>
* Uses an ISO 8601 date-time for <code>dtreviewed</code>
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* Uses fixed-point integer values from <var>0</var>-<var>5</var> for <code>rating</code> (publishers may, for example, display a percentage rating)
 
===hAtom===
===hAtom===
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* Uses ISO 8601 for track <code>duration</code>, e.g. <code>PT3M23S</code>
* Uses ISO 8601 for track <code>duration</code>, e.g. <code>PT3M23S</code>
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== Misconceptions of Fixed Data Formats in Microformats==
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There are also cases (at least one) of apparent fixed data formats in microformats which should not require the providing of a separate value.  It is useful to document these as a way to clear up apparent misconceptions.
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===hReview===
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* ''Uses fixed-point integer values from <var>0</var>-<var>5</var> for <code>rating</code> (publishers may, for example, display a percentage rating)''
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There are several misconceptions here.
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# The ''default'' rating values in [[hReview]] are [[hreview#In_General|from 1.0-5.0]] (not 0-5)
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# hReview permits the author to state their own 'worst' to 'best' range for any given 'rating'.
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Thus a publisher that wants to display a percentage rating can do so by simply specifying a 'worst' value for a rating of 0, and a 'best' value for a rating of 100.  Then the actual percentage rating can simply be marked up inline and no separate machine value is necessary.
==Embedding Fixed Data Formats in Microformats==
==Embedding Fixed Data Formats in Microformats==

Revision as of 02:10, 3 May 2009

Machine Data in Microformats

Contents


Microformats are designed to mark-up human consumable information, as commonly found in the wild. But, in a number of exceptional cases it has been necessary to specify precise data formats for particular properties. Formats for dates, times and locations are standardised in a way that doesn't always match the way information is visibly published. This is necessary to make the data understandable to parsers. Similarly, there are keywords in hCard that must be written in English (telephone ‘type’ in hCard, for example).

It is necessary for these data formats to be fixed to make the data parsable by machines; the cost for a parser to support every commonly published date-time format in the world (include approximations like ‘five minutes ago’) is too high, as is handling international translation (such as mobile telephones; US-English ‘cell’ published as British English ‘mobile’).

In some cases, the human version of the data can be semantically described as an abbreviated form of the machine data, and the machine data may also be human consumable. For example, the date-design-pattern uses HTML's abbr element to expand one human date representation into the ISO 8601 form date: ‘January 1st’ is an abbreviated form of ‘2008-01-01’. The latter is also legible to humans (and can be exposed to them through tool-tips and assistive screen readers).

In other cases, this machine data is not legible to humans. In hAudio, the duration property uses ISO 8601, resulting in machine data of PT3M23S; not understandable to humans, and therefore not a valid expansion of ‘three minutes and twenty-three seconds’.

Cases of Fixed Data Formats in Microformats

The following are all current uses of fixed format machine data required by the various microformats.

hCalendar

hCard

hReview

hAtom

hResume

Geo

hAudio

Misconceptions of Fixed Data Formats in Microformats

There are also cases (at least one) of apparent fixed data formats in microformats which should not require the providing of a separate value. It is useful to document these as a way to clear up apparent misconceptions.

hReview

There are several misconceptions here.

  1. The default rating values in hReview are from 1.0-5.0 (not 0-5)
  2. hReview permits the author to state their own 'worst' to 'best' range for any given 'rating'.

Thus a publisher that wants to display a percentage rating can do so by simply specifying a 'worst' value for a rating of 0, and a 'best' value for a rating of 100. Then the actual percentage rating can simply be marked up inline and no separate machine value is necessary.

Embedding Fixed Data Formats in Microformats

There are currently three supported methods of including these fixed data formats in a microformatted document.

As Visible Page Content

You may use the standard class-design-pattern to mark-up the data visibly in the page.

Ben was born on <span class="bday">1984-02-09</span>.

We're meeting up on Northumberland Avenue (<span class="geo">51.507033,-0.126343</span>).

As An Abbreviation

In some cases, the data formats specified make valid expansions of common human forms, such as dates in in an hCard birthday field:

Ben was born on <abbr class="bday" title="1984-02-09">9th February</abbr>

Note, however, that not all data formats are valid expansions. In HTML, the abbr element is working semantically at a text level, not a data level. Both the abbreviated form (the inner text) and the expanded form (the title) need to be consumable by humans.

This means that in hAudio, using an abbreviation for duration is incorrect:

<abbr class="duration" title="PT3M23S">3 minutes, 23 seconds</abbr>

Whilst the data ‘PT3M23S’ is an expanded form of ‘3 minutes, 23 seconds’, the text is not; ‘PT3M23S’ is nonsense to most human beings. abbr is an element that describes the text, not the data. HTML4 has no way to mark up arbitrary data.

As supplementary data using the value-excerption-pattern

The machine data form can be included alongside any human legible text, and hidden using another layer of the browser stack (namely, CSS). This behavior is documented as the value-excerption-pattern, and derived from the value excerpting behavior in hCard.

So, for example, when describing a location by name, but still wanting to include geo for the machine-readable location:

<span class="geo">Northumberland Avenue, London <span class="value">51.507033,-0.126343</span></span>

Then, optionally use CSS to hide the data you don't want displayed:

.geo > .value { display: none; }

The same pattern works for the hAudio duration example given above:

<span class="duration">3 minutes and 23 seconds <span class="value">PT3M23S</span></span>

And again, the optional CSS:

.haudio .duration > .value { display: none; }

Of course, this does result in a dependency on CSS to make the data invisible to users, and will result in the machine data being displayed alongside the human form in any user agent without CSS support. That's a compromise that has to be resolved based on the requirements of individual sites.


Proposed Methods

As Invisible Supplementary Data

The main content of this section — focussing just on using the value-excerption-pattern in a mark-up level hidden manner — has been moved into value-excerption-pattern-issues for easier tracking.

These are proposals and therefore should be noted that they are not endorsed or supported. You should not use any of these patterns when publishing a page, but may like to get involved to help develop these ideas.

Proposals for more publisher-friendly mark-up for machine-data

A final suggestion is that on a case-by-case basis, all the above documented machine-data patterns could be reworked in a human accessible, publisher compatible, internationalizable and machine-parsable manner. Previously, such solutions have not been forthcoming.

Acknowledgements

Related Pages

machine-data was last modified: Wednesday, December 31st, 1969

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