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 (″)

Value 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	Symbols	Aliases
metre	m	meter
gram	g	gramme
second	s, sec
ampere	A	amp
candela	cd
mole	mol
kelvin	K, ℚ (U+211A)
newton	N
pascal	Pa
joule	J
watt	W
coulomb	C
volt	V
ohm	Ω (U+03A9), Ω (U+2126)
siemens	S
farad	F
weber	Wb
henry	H
tesler	T
hertz	Hz
byte	B
bit	b
litre	L, l, ℓ (U+2113)	liter
Celsius	℃ (U+2103), °C (U+00B0 followed by captial C)
radian	rad

The following SI prefixes MUST be supported.

10ⁿ	Prefix	Symbol
10²⁴	yotta-	Y
10²¹	zetta-	Z
10¹⁸	exa-	E
10¹⁵	peta-	P
10¹²	tera-	T
10⁹	giga-	G
10⁶	mega-	M
10³	kilo-	k
10²	hecto-	h
10¹	deca-	da
10⁰	(none)	(none)
10⁻¹	deci-	d
10⁻²	centi-	c
10⁻³	milli-	m
10⁻⁶	micro-	µ (U+00B5), μ (U+03BC), u
10⁻⁹	nano-	n
10⁻¹²	pico-	p
10⁻¹⁵	femto-	f
10⁻¹⁸	atto-	a
10⁻²¹	zepto-	z
10⁻²⁴	yocto-	y

The full names and for SI prefixes MUST only be combined with the full names for the units (or their aliases). Likewise the symbols for SI prefixes MUST only be combined with the symbols for the units.

kilometre
milligramme
μL
mΩ
microV (Invalid)
kgram (Invalid)

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
Jukka Korpela - Characters in SI notations

measure

Contents

Measure microformat

The problem

Draft Schema

Standard Measure Schema

Angular Measure Schema

Money Schema

Value

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

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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