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  1. OMG Issue

SYSML14 — QUDV's support for measurement scales is impractical

  • Key: SYSML14-31
  • Legacy Issue Number: 18681
  • Status: closed  
  • Source: NASA ( Dr. Nicolas F. Rouquette)
  • Summary:

    The QUDV conceptual model in SysML 1.3 provides 2 concepts intended to support the modeling of measurement scales:

    D.5.2.13 Scale (for defining a measurement scale in the sense of the Vocabulary of International Metrology (VIM))

    D.5.2.14 ScaleValueDefinition (for representing a specific value for a measurement scale)

    D.5.2.13 mentions a simple example of a "priority" measurement scale whose scale value definitions would be 0 for "low", 1 for "medium" and 3 for "high".

    In practice, a user can reasonably expect to use a suitably-defined "priority" measurement scale as the type of a SysML value property.

    Unfortunately, this requires defining the "priority" measurement scale twice:

    Per QUDV, a definition of "priority" as an InstanceSpecification classified by QUDV::Scale so that it can specify its "low", "medium" and "high" values defined as InstanceSpecifications classified by QUDV::ScaleValueDefinition
    For typing a value property, a definition of "priority" as a SysML ValueType Enumeration whose EnumerationLiterals correspond to “low”, “medium” and “high”
    From a metrology standpoint, both definitions of “priority” can be related to a definition of a Unit and a definition of a QuantityKind:

    • The QUDV-based definition of “priority” can refer to a definition of a Unit; a given QuantityKind definition can refer to the QUDV “priority” scale (See SysML 1.3, Figure D.8 in section D.5.2)
    • The ValueType-based definition of “priority” can refer to a definition of a Unit and to a definition of a QuantityKind via the SysML ValueType stereotype properties (See SysML 1.3, Figure 8.4 in section 8.3.2)

    From a pragmatic standpoint, the QUDV-based definition has no utility beyond QUDV purposes whereas the ValueType-based definition of “priority” is clearly useful for typing value properties and specifying their values.

    Suggest merging the two approaches, explaining that QUDV::Scale and QUDV::ScaleValueDefinition can be deleted from the spec since:

    • A SysML::ValueType Enumeration really defines a “scale”, thereby alleviating the need for a separate QUDV::Scale concept.
    • The EnumerationLiterals of a SysML::ValueType Enumeration constitute the ordered set of values for a “scale”, thereby alleviating the need for a separate QUDV::ScaleValueDefinition concept.


  • Reported: SysML 1.3 — Sun, 21 Apr 2013 04:00 GMT
  • Disposition: Resolved — SysML 1.4
  • Disposition Summary:

    Follow the proposed suggestion except that providing explanations for modeling
    “scales” using SysML ValueTypes and SysML Enumeration ValueTypes is
    postponed until after peer review.
    This resolution builds on the resolution to issue 18269 from SysML 1.4 Ballot 4 and
    issue 18435 from SysML 1.4 Ballot 5.

  • Updated: Fri, 6 Mar 2015 20:58 GMT