measure

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 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
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
10002/3	102	hecto-	h	1795	Hundred		100
10001/3	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:

• <span class="unit">kg m / s</span>
• <span class="unit">m/s^2</span>
• <span class="unit">meter³</span>
• <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).

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 SHOULD provide a rel=glossary link to a page that defines the units.

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.

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 and type) 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>

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 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

See also

• measure
• measure-formats
• measure-examples
• measure-brainstorming
• currency