SWE Common Data Model OGC 08-094r1
and vertical errors are given along with the geographic position. See the XML implementation clause for more information on this use case.
7.2.16 NilValues Class
The “NilValues” class is used by all classes deriving from “AbstractSimpleComponent”. It allows the specification of one or more reserved values that may be included in a data
stream when the normal measurement value is not available see clause 6.4.2. The UML model of this class is given below:
«Type»
NilValues
«DataType»
Basic Types::NilValue
«property» +nilValue
1.. «property»
+ reason: ScopedName + value: CharacterString
Figure 7.19 – NilValues Class
An instance of the “NilValues” class is composed of one to many “NilValue” objects, each of which specifies a mapping between a reserved value and a reason.
The mandatory “reason” attribute indicates the reason why a measurement value is not available. It is a resolvable reference to a controlled term that provides the formal textual
definition of this reason usually agreed upon by one or more communities.
Requirement
http:www.opengis.netspecSWE2.0requml-simple-componentsnil-reason-resolvable
Req 34. The “reason” attribute of an instance of the “NilValue” class shall map to
the complete human readable definition of the reason associated with the NIL
value.
The mandatory “value” attribute specifies the data value that would be found in the stream to indicate that a measurement value is missing for the corresponding reason. The
range of values allowed here is the range of values allowed by the datatype of the parent data component.
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OGC 08-094r1 SWE Common Data Model
Requirement
http:www.opengis.netspecSWE2.0requml-simple-componentsnil-value-type-coherent
Req 35. The value used in the “value” property of an instance of the “NilValue”
class shall be compatible with the datatype of the parent data component object.
This means that when specifying NIL values for a “Quantity” component, only real values are allowed in most implementations, this includes NaN, -INF and INF and for a
“Count” component only integer values are allowed.
Consequently, it is also impossible to specify NIL values for a “Boolean” data component since it allows only two possible values. In this case a “Category” component should be
used.
There are no restrictions on the choice of NIL values for “Category” and “Text” components since their datatype is String.
7.2.17 AllowedTokens Class
The “AllowedTokens” class is used to express constraints on the value of a data component represented by a “Text” or a “Category” class. The UML class is shown
below:
Allow edTokens
«property» + value: CharacterString [0..]
+ pattern: CharacterString [0..1]
Figure 7.20 – AllowedTokens Class
This class allows defining the constraint either by enumerating a list of allowed values by using one or more “value” attributes andor by specifying a pattern that the value must
match. The value must then either be one of the enumerated tokens or match the pattern.
7.2.18 AllowedValues Class
The “AllowedValues” class is used to express constraints on the value of a data component represented by a “Count” or a “Quantity” class. The UML class is shown
below:
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