OGC 08-094r1 SWE Common Data Model
6.2 Data Representation
Data representation deals with how property values are represented and stored digitally. Each component or field in a dataset carries a value that represents the state of a
property. This representation will vary depending on the nature of the method used to capture the data andor the target usage. For instance, a fluid temperature can be
represented as a decimal number expressed in degrees Celsius i.e. 25.4 °C, or as a categorical value taken from a list of possible choices such as “freezing, cold, normal,
warm, hot”.
The following types of representations have been identified: Boolean, Categorical, Continuous Numerical, Discrete Countable and Textual. The paragraphs below explain
basic features of each of these representation types.
6.2.1 Boolean
A Boolean representation of a property can take only two values that should be “truefalse” or “yesno”. In a sense, this type of representation is a particular case of the
categorical representation with only two predefined options.
Examples
Motion detectors output can be represented by a boolean value – TRUE if there is motion in the room, FALSE otherwise.
OnOff status of a measurement system can be represented by a boolean value – TRUE if the system in on, FALSE if the system is off.
Requirement
http:www.opengis.netspecSWE2.0reqcoreboolean-rep-valid
Req 2. A boolean representation shall at least consist of a boolean value.
The “Boolean” data type detailed in clause 7.2.4 is used to define a data component with a Boolean representation.
6.2.2 Categorical
A categorical representation is a type of discrete representation of a property that only allows picking a value from a well defined list of possibilities i.e. categories. This list is
called a code space in this standard, following ISO 19103 terminology.
The different possible values constituting a code space are usually listed explicitly in an out-of-band dictionary or ontology. This is necessary because each value should be
defined formally and unambiguously, so that it can be interpreted correctly.
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SWE Common Data Model OGC 08-094r1
Examples
Biological or chemical species data is usually represented by a categorical data component that can leverage on existing controlled vocabulary.
A camera mode can be represented by a categorical value – AUTO_FOCUS, MANUAL_FOCUS, etc…
Requirement
http:www.opengis.netspecSWE2.0reqcorecategorical-rep-valid
Req 3. A categorical representation shall at least consist of a category identifier and
information describing the value space of this identifier.
The “Category” data type detailed in clause 7.2.6 is used to define a data component with a categorical representation.
6.2.3 Numerical continuous
Perhaps the most used representation of a property value, especially in the science and technical communities, is the numerical one, as the majority of properties measured by
sensors can be represented by numbers.
Numerical representation is often used for continuous values and, in this case, the representation consists of a decimal often floating point number associated to a scale or
unit of measure. The unit specification is mandatory even for quantities such as ratios that have no physical unit in this case a scale factor is provided such as 1, 1100 for percents,
11000 for per thousands, etc..
Examples
Temperature measurements can be represented by a number associated to a unit such as degrees Celsius or Fahrenheit – 23.51°C, 94°F
A velocity vector is composed of several values usually 2 or 3 associated to a unit of speed – [1.0 2.0 3.0] ms.
Requirement
http:www.opengis.netspecSWE2.0reqcorenumerical-rep-valid
Req 4. A continuous numerical representation shall at least consist of a decimal
number and the scale or unit used to express this number.
The “Quantity” data type detailed in clause 7.2.8 is used to define a data component with a decimal representation and a unit of measure.
Copyright © 2011 Open Geospatial Consortium
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