Measure microformat

Currently this microformat is in exploratory stage. Contributions should focus on real examples from the Web, existing formats/encoding of measures.

The problem

Measures (e.g. weights, sizes, temperatures) occur frequently on the Web, they are constituted of a value a unit-measure and, in scientific and technical contexts, an experimental uncertainty. These 3 elements should be marked-up consistently across websites so that they can be easily identified and acted upon (export, compute, convert) in collaborative distributed applications.

Unit-measures differ from locale to locale (e.g. Fahrenheit vs. Celsius, pound versus Kilogram), making comparison and matching of offerings difficult.

The Measurement microformat will enable unambiguous description of physical quantities and thus provide a solid ground for data sharing and automation in many areas.

Draft Schema

Rationale: The names "value" and "type" are taken from hCard; "item" is used from hReview.

Standard Measure Schema

hmeasure
- value {1} (numeric)
- unit {1} (unit)
- item? (text | hCard | hCalendar)
- type ? (text, e.g. "height", "width", "weight")
- tolerance ? (percentage | hmeasure)

Angular Measure Schema

hmeasure
- value {1} (degree)
- item? (text | hCard | hCalendar)
- type ? (text, e.g. "angle of elevation")
- tolerance ? (percentage | hmeasure)

Money Schema

hmoney
- value {1} (numeric)
- unit {1} (ISO 4217 code)
- tolerance ? (percentage | hmoney)

Value

Arbitrary white space MAY be included in the value to improve readability. Parsers MUST strip out all white space before further processing.

In the standard and money schemas, the value MUST be a number, formatted according to the following EBNF pattern:

non-zero-digit = "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" ;
digit          = "0" | non-zero-digit ;
natural        = non-zero-digit , {digit} ;
integer        = "0" | [ "-" ] , natural ;
dot-decimal    = integer , "." , {digit} ;
comma-decimal  = integer , "," , {digit} ;
e-sign         = "e" | "E" ;
mantissa       = dot-decimal | comma-decimal | integer ;
sci-number     = mantissa , e-sign , integer ;
number         = dot-decimal | comma-decimal | integer | sci-number ;

This roughly corresponds to a subset of C syntax for floating points and integers, excluding octal and hexadecimal representations. However, note that both commas and stops may be used as decimal points.

The Unicode minus sign (U+2212) and ASCII-compatible hyphen-minus (U+002D) MUST both be treated as acceptable indicators of a negative number. In addition, the symbols ¼ (U+00BC), ½ (U+00BD) and ¾ (U+00BE) SHOULD be supported as aliases for 0.25, 0.5 and 0.75 respectively.

In the angular measure schema, a measure is expressed as a combination of up to three numeric components: called degrees, minutes and seconds. Any combination of these components may be used, except when degrees and seconds are given minutes MUST be present. The components MUST appear in the correct order (degrees, minutes, seconds). Each component must match the production rule for "mantissa" above, with the following additional constraints:

Only the first component can bear a minus sign. Subsequent components "inherit" the negativity (or lack thereof) from their predecessors.
All components except the last must match the production rule for "integer".

The numeric components MUST be indicated by appending a suffix to each component. Valid suffixes are:

degree: "deg", U+00B0 degree symbol (°)
minute: "min", straight single quote ('), U+2032 prime (′)
second: "sec", straight double quote ("), U+2033 double prime (″)

Examples

1729 (the smallest number that can be expressed as the sum of two cubes in two different ways)
1.61803399 (the golden ratio)
2,99792458e8 (the speed of light in a vacuum, measured in metres per second)
-40 (value at which Celcius and Farenheit scales are equal)
1,000,000,000 (Invalid: commas may be used as decimal points, but not for grouping thousands.)
57.2958 deg (1 radian, in degrees)
-57° 17′ 45.1″ (-1 radian, in degrees, minutes and seconds)
4° 30″ (Invalid: no minutes)
4° -30′ (Invalid: only first component may be negative)

Unit

In the standard schema, the "unit" class is defined as an arbitrary string. Any unit may be used, but authors SHOULD attempt to use official SI units of measurement where appropriate. Parsers MUST recognise the following case-sensitive list of units, derived from the SI list of base units and official recognised derived units, with the addition of bits and bytes, which are commonly used on web pages, and litres, degrees Celsius and radians. (Note that gram appears in this table instead of kilogram. This is deliberate.)

Unit	Aliases
metre	meter, m
gram	gramme, g
second	sec, s
ampere	amp, A
candela	cd
mole	mol
kelvin	K
newton	N
pascal	Pa
joule	J
watt	W
coulomb	C
volt	V
ohm	Ω
siemens	S
farad	F
weber	Wb
henry	H
tesler	T
hertz	Hz
byte	B
bit	b
litre	liter, L
Celsius	℃ (U+2103), °C (U+00B0 followed by captial C)
radian	rad

The following SI prefixes MUST be supported (table taken from Wikipedia - it needs rewriting to remove irrelelevent columns). "u" MUST be treated as an alias for "μ".

SI prefixes
1000ⁿ	10ⁿ	Prefix	Symbol	Since^[1]	Short scale	Long scale	Decimal equivalent in SI writing style
1000⁸	10²⁴	yotta-	Y	1991	Septillion	Quadrillion	1 000 000 000 000 000 000 000 000
1000⁷	10²¹	zetta-	Z	1991	Sextillion	Trilliard (thousand trillion)	1 000 000 000 000 000 000 000
1000⁶	10¹⁸	exa-	E	1975	Quintillion	Trillion	1 000 000 000 000 000 000
1000⁵	10¹⁵	peta-	P	1975	Quadrillion	Billiard (thousand billion)	1 000 000 000 000 000
1000⁴	10¹²	tera-	T	1960	Trillion	Billion	1 000 000 000 000
1000³	10⁹	giga-	G	1960	Billion	Milliard (thousand million)	1 000 000 000
1000²	10⁶	mega-	M	1960	Million		1 000 000
1000¹	10³	kilo-	k	1795	Thousand		1 000
1000^2/3	10²	hecto-	h	1795	Hundred		100
1000^1/3	10¹	deca-	da	1795	Ten		10
1000⁰	10⁰	(none)	(none)	NA	One		1
1000^−1/3	10⁻¹	deci-	d	1795	Tenth		0.1
1000^−2/3	10⁻²	centi-	c	1795	Hundredth		0.01
1000⁻¹	10⁻³	milli-	m	1795	Thousandth		0.001
1000⁻²	10⁻⁶	micro-	µ	1960^[2]	Millionth		0.000 001
1000⁻³	10⁻⁹	nano-	n	1960	Billionth	Milliardth	0.000 000 001
1000⁻⁴	10⁻¹²	pico-	p	1960	Trillionth	Billionth	0.000 000 000 001
1000⁻⁵	10⁻¹⁵	femto-	f	1964	Quadrillionth	Billiardth	0.000 000 000 000 001
1000⁻⁶	10⁻¹⁸	atto-	a	1964	Quintillionth	Trillionth	0.000 000 000 000 000 001
1000⁻⁷	10⁻²¹	zepto-	z	1991	Sextillionth	Trilliardth	0.000 000 000 000 000 000 001
1000⁻⁸	10⁻²⁴	yocto-	y	1991	Septillionth	Quadrillionth	0.000 000 000 000 000 000 000 001
Notes: 1. The 1795 dates identify prefixes in use since the metric system was introduced. The other dates are not necessarily dates of first use, but rather the date of recognition by a resolution of the CGPM, which first met in 1889. 2. The micron was earlier recognized by the CGPM in 1948; that decision was abrogated in 1967-68.

Combining units

Units may be multiplied by separating with whitespace, or divided using a slash (/) or U+2215 division slash (∕). Units may be raised to an integer power using a caret character. The unicode superscript numerals 2 to 9 (U+00B2, U+00B3, U+2074-79) MUST be supported as aliases for raising to the appropriate integer powers. Multiplication is more associative than division.

Examples:

kg m / s
m/s^2
meter³
<abbr class="unit" title="μm">micron</abbr>

Angular units

Units MUST NOT be given for measurements expressed in the degree schema: the degree itself is the unit. If the standard schema is used, units may be given in radians (rad).

Other / Non-SI Units

Authors MAY specify units other than those defined above, but SHOULD NOT assume that parsers will be able to interpret them. Authors using other units MAY provide a rel=glossary link to a page or fragment that defines the units.

Explicitly Defining a Unit

hmeasure may be used with the <dfn> element to explicitly define a unit in terms of pre-defined units. The "title" attribute (if any) is taken to be an alias of the unit name.

<p class="hmeasure" id="dfn-inch">
  An <dfn class="item" title="in">inch</dfn> is defined as
  <span class="value">0.0254</span> <span class="unit">m</span>.
</p>

Other instances of hmeasure may then refer to this definition, implicitly:

<p class="hmeasure">
  The <span class="item">action figure</span> has a <span class="type">height</span> of
  <span class="value">5</span> <span class="unit">in</span>.
</p>

or explicitly:

<p class="hmeasure">
  The <span class="item">action figure</span> has a <span class="type">height</span> of
  <span class="value">5</span>
  <a class="unit" rel="glossary" href="#dfn-inch">in</a>.
</p>

Currency Units

If the money schema is being used, the unit is not an arbitrary string. It MUST be a three-letter ISO 4217 code. The following aliases for the four largest reserve currencies (as of 2008) are allowed:

Unit	Aliases
EUR	€
GBP	£
JPY	¥
USD	$

Other currencies MAY be displayed using these symbols only through the ABBR design pattern:

<span class="hmoney">
  <abbr class="unit" title="AUD">$</a><span class="value">5.00</span>
</span>

Item

An hCard, hCalendar event or textual description of the item being measured may be supplied.

<p class="hmeasure">
  <span class="item vcard">The <span class="fn">Great Wall</span>of
  <span class="adr"><span class="country-name">China</span></span></span>
  is about <span class="value">6 700</span> <abbr title="km">kilometres</abbr>
  <abbr title="length" class="type">long</abbr>.
</p>

The item is optional.

Type

The type specifies the dimension being measured. A measurement in, say, metres may be ambiguous because it could refer to a depth, a height, a length or a width. The optional type parameter allows you to specify a human-readable dimension.

Tolerance

An optional tolerance may be specified as a percentage or as a nested hmeasure/hmoney.

Examples:

<span class="hmeasure">
  <span class="type">Height</span>:
  <span class="value">5</span> <span class="unit">m</span>
  ± <span class="tolerance">2%</span>
</span>

<span class="hmoney">
  <span class="unit">$</span><span class="value">5.00</span>
  ± <span class="tolerance hmoney"><span class="unit">$</span><span class="value">1.00</span></span>
</span>

When no tolerance is provided, a default tolerance of 0% MUST NOT be assumed — the tolerance is simply unknown.

Minimisation Techniques

hmeasure

If no "value" is given, then the first number conforming to the EBNF above is taken to be the value. If no unit is given, then the entire string within the "hmeasure" (less the value, item, type and tolerance) is taken to be the unit.

For example:

<span class="hmeasure">3 pints <span class="item">beer</span></span>

Value: 3
Unit: "pints"
Item: "beer"

<span class="hmeasure">4 m</span>

Value: 4
Unit: metre

Open question: what about cases where there is no white space? SI says white space should always separate the quantity and unit, but in practice, many people do not include white space in measures.

hmoney

If no "value" is given, then the first number conforming to the EBNF above is taken to be the value. If no "unit" is given, the first three-letter word (or single character alias) is taken to be the unit. White space between the implied unit and value is considered optional. The following are to be equivalent:

<span class="hmoney"><span class="unit">EUR</span> <span class="value">1,00</span></span>
<span class="hmoney">EUR <span class="value">1,00</span></span>
<span class="hmoney">EUR1,00</span>
<span class="hmoney">1,00 EUR</span>
<span class="hmoney">1.00 <abbr class="unit" title="EUR">euro</abbr></span>
<span class="hmoney">€1,00</span>
<abbr class="hmoney" title="EUR 1,00">a euro</abbr>

Minimising Tolerence

If the tolerance is not a percentage (i.e. it is a nested hmeasure/hmoney) and it does not contain a unit (either explicit, or by minimisation rules), then the unit is taken to be the unit of the parent hmeasure/hmoney.

If no explicit tolerance is given, the hmeasure string should be examined for an occurrence of the substring "±". If this is present, the substring after it, and continuing to the end of the hmeasure string is taken to be a tolerance. If the tolerance contains a "%" character, the tolerance is taken to be a percentage. Otherwise is it taken to be an implicit nested hmeasure/hmoney.

Worked example

The following example shows a series of expansions taken by a parser encountering a minimised hmoney:

<span class="hmoney">$1.54 ± 0.01</span>

The "±" sign introduces a tolerance, which does not include a "%" symbol, so is treated as a nested hmoney.

<span class="hmoney">$1.54 ±<span class="hmoney tolerance">0.01</span></span>

No explicit units or values are given in either hmoney, so units and values are extracted as per hmoney minimisation:

<span class="hmoney"><span class="unit">$</span><span class="value">1.54</span>
±<span class="hmoney tolerance"><span class="value">0.01</span></span></span>

The nested hmoney contains no unit, so it inherits its unit from the parent hmoney:

<span class="hmoney"><span class="unit">$</span><span class="value">1.54</span>
±<span class="hmoney tolerance"><span class="unit">$</span> <span class="value">0.01</span></span></span>

Parsed values:

Unit: USD
Value: 1.54
Tolerance:
- Unit: USD
- Value: 0.01

Examples

An example weather forecast using hmeasure, adr, geo and hCalendar with the include pattern:

<div>
    Weather for
    <span id="loc-lewes">
        <span class="adr location">
            <span class="locality">Lewes</span>,
            <span class="region">East Sussex</span>
        </span>
        (<span class="geo">50.8730;0.005</span>)
    </span>,
    <span class="vevent item" id="day-20080325">
        <a class="include" href="#loc-lewes"></a>
        <span class="summary">Tuesday</span>
        <abbr class="dtstart" title="2008-03-25">25 March</abbr>
        <abbr class="dtend" title="2008-03-26"></abbr>
    </span>:
    <span class="hmeasure">
        <a class="include" href="#day-20080325"></a>
        <abbr title="Maximum temperature" class="type">High</abbr>
        8 ℃
    </span>,
    <span class="hmeasure">
        <a class="include" href="#day-20080325"></a>
        <abbr title="Minimum temperature" class="type">Low</abbr>
        0 ℃
    </span>
</div>

(The above example does not necessarily represent best practice. Authors should make themselves aware of the accessibility issues currently being discussed around the include and abbr design patterns.)

Parsing Hints

This section is informative. Parsers should note that (with the exception of certain non-ascii characters, which can be converted manually first) all the pre-defined non-currency units can be understood by the GNU units program. A parser could act as a wrapper to a GNU units installation, or make use of a GNU units-based web service to convert between units.

Related microformats

hcalendar can provide a complete quantitative description of a natural event (for example an earthquake) occurring at a specified time (dtstart/dtend) and location (embedded geo), by just embedding measured physical quantities in the 'descrition' span.
job-listing can use time measure for specify per what period of time the salary is for.
hlisting product dimensions; weight/mass; time period (as above).
directions-examples can use length measure for mileage and time to go from one point to the next.
recipe-examples can use weight, volume and time measure for ingredients and preparation time.
currency can be viewed as a measurement unit, or as a component of a measurement unit, as in $ per hour.

Contributors

Guillaume Lebleu
Andy Mabbett
Luca Postpischl
Manu Sporny
TobyInk

References

Measurement in scientific/technical contexts (Wikipedia)
Scientific notation for Physical quantities (Wikipedia)
International System of Units (SI)
- (Wikipedia)
the Semantic ChemicalWeb (GoogleEng presentation, Peter Murray-Rust)
the New e-Science (SlideShare, David De Roure)
Wikipedia's "convert" template

measure

Contents

Measure microformat

The problem

Draft Schema

Standard Measure Schema

Angular Measure Schema

Money Schema

Value

Examples

Unit

Combining units

Angular units

Other / Non-SI Units

Explicitly Defining a Unit

Currency Units

Item

Type

Tolerance

Minimisation Techniques

hmeasure

hmoney

Minimising Tolerence

Worked example

Examples

Parsing Hints

Related microformats

Contributors

References

See also

Navigation menu

measure

Measure microformat

The problem

Draft Schema

Standard Measure Schema

Angular Measure Schema

Money Schema

Value

Examples

Unit

Combining units

Angular units

Other / Non-SI Units

Explicitly Defining a Unit

Currency Units

Item

Type

Tolerance

Minimisation Techniques

hmeasure

hmoney

Minimising Tolerence

Worked example

Examples

Parsing Hints

Related microformats

Contributors

References

See also

Navigation menu

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