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  1. OMG Issue

SYSML13 — Improvements to QUDV for SysML v1.3

  • Key: SYSML13-57
  • Legacy Issue Number: 16396
  • Status: closed  
  • Source: Thematix Partners LLC ( Roger Burkhart)
  • Summary:

    There are mistakes and inconveniences in the model and model library of quantities, units, dimensions and values (QUDV) in SysML v1.2 as defined in Annex C. Furthermore the ordering of the sections in Annex C can be made more logical to improve the readability.

  • Reported: SysML 1.2 — Mon, 25 Jul 2011 04:00 GMT
  • Disposition: Resolved — SysML 1.3
  • Disposition Summary:

    Remove Quantity from Annex C.5. The reason is that the concept of quantity is
    fully implemented by a value property typed by a ValueType. Therefore an
    additional class/block Quantity is superfluous and confusing.
    The QUDV model can be simplified by merging DimensionFactor and
    QuantityKindFactor into one concept QuantityKindFactor.
    Remove property definition for symbolicExpression, since this is only an
    informational (presentation) property that can be derived from the ordered set of
    factor : DimensionFactor.
    In SysML 1.2, Figure C.8, a SystemOfUnits had a many-to-many relationship
    with SystemOfQuantities. This precluded aligning SysML 1.2 QUDV tightly with
    ISO 80000-1:2009 where the notion of ‘system of units’ (ISO 80000-1:2009, 3.13)
    is defined for a single ‘system of quantities’ (ISO 80000-1:2009, 3.3).
    Furthermore, Section C.5.2.22 Unit did not define the property Unit::quantityKind
    : QuantityKind[0..1] shown in Figure C.8 even though this property is extensively
    used for the specification of coherence analysis in section C.5.2.21
    SystemOfUnits, Constraints [1,2].
    The meaning of the undocumented association between Unit and QuantityKind
    should be revised to support the capability specified in ISO/IEC Guide 99:2007
    about a coherent system of units (item 1.14), Note 1:
    A system of units can be coherent only with respect to a system of
    quantities and the adopted base units. The adoption of a Unit as the base measurement unit for a given QuantityKind is
    understood to be a distinguished subset among the set of all QuantityKinds that
    are the measurementUnits for a particular Unit. A Unit can be the measurement
    unit of many QuantityKinds and a given QuantityKind can have many
    measurement Units per Note 2 of ISO 80000-1:2009, 3.9:
    NOTE 2 Measurement units of quantities of the same quantity dimension
    may be designated by the same name and symbol even when the
    quantities are not of the same kind. For example, joule per kelvin and J/K
    are respectively the name and symbol of both a measurement unit of heat
    capacity and a measurement unit of entropy, which are generally not
    considered to be quantities of the same kind. However, in some cases
    special measurement unit names are restricted to be used with quantities
    of specific kind only. For example, the measurement unit ‘second to the
    power minus one’ (1/s) is called hertz (Hz) when used for frequencies and
    becquerel (Bq) when used for activities of radionuclides. As another
    example, the joule (J) is used as a unit of energy, but never as a unit of
    moment of force, i.e. the newton metre (N ยท m).
    The above makes sense in the context of a particular relationship between a
    SystemOfUnits and a SystemOfQuantities. It would be more difficult to express
    the above in a more generalized context like that of SysML1.2 with many-tomany
    possible relationships between SystemOfUnits and SystemOfQuantities.
    Consequently, the QUDV model is revised to focus on the most common case in
    practice where a SystemOfUnits is defined for up to a single SystemOfQuantities.
    The reduced generality of the QUDV model is intended to simplify the use of
    QUDV in practice and is explicitly conveyed via new invariants (see below for
    new constraints added for C.5.2.20 and C.5.2.21).
    In SysML 1.2, Figure C.10 is not consistent with the text which includes OCL for
    deriving the non-derived property SystemOfQuantities::dimension :
    Dimension[0..*] (see C.5.2.20 SystemOfQuantities, Constraint [1])
    Since SysML 1.2 was published, the major parts of ISO/IEC 80000 have been
    published with definitions for the International System of Quantities (ISQ) and the
    International System of Units (SI). Annex C.4 is revised to be based on this
    authoritative source rather than the NIST special publication it formerly
    referenced. The SysML QuantityKind and Unit definitions in Annex C.4 are
    revised to follow the naming and organization of the quantity and unit definitions
    from Part 1 of ISO 80000, which cover the same base and derived units as
    before. Unit symbols have also been added to the SysML Unit definitions.
    The text in Annex C.4 is revised to indicate how the definitionURI strings of its
    QuantityKind and Unit definitions could be used to refer to corresponding QUDV
    definitions in a separately published model library. Figures C.10 and C.11 in
    Section 5.4.1 continue to provide examples of such QUDV definitions that could
    be expanded to the full set of quantities and units from ISO 80000-1.
    Specific definitionURI string values for reference to QUDV definitions have not
    been included in Annex C.4, not only because they would clutter the diagrams,
    but because they could be automatically supplied as part of the publication of
    more complete, machine-readable versions of both model libraries.
    Because Annex C.4 continues to define a model library consisting only of SysML
    QuantityKind and Unit definitions, without any direct dependence on QUDV or
    other QUDV model libraries, there is no inherent problem with the ordering or
    logical dependence of the current Annexes. No change is made to the current
    Annex C sections other than a new name for the ISO 80000-1 model library in
    Section C.4.

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