SMM — Clarify role of NamedMeasure

Scales of Measurement are a fundamental property of a measure describing the allowable mathematical transformations that can be legitimately applied to it.

Discussion:
Attached are some URLs that will give you an overview of Scales of Measurement. They are a fundamental property of a measure describing the allowable mathematical transformations that can be legitimately applied to it. Since they therefore determine the statistical methods that can be applied to the measure, they need to be treated as a first level attribute of a measure.
http://www.math.sfu.ca/~cschwarz/Stat-301/Handouts/node5.html
http://en.wikipedia.org/wiki/Scale_of_measurement (not always written in easily understood terms)
http://www.wadsworth.com/psychology_d/templates/student_resources/workshops/stat_workshp/scale/scale_01.html (tutorial - behavioral science view)

Summary of change:
· Add enumeration MeasurementScale
o Add enu ordinal, nominal, interval and ratio.
· Add attribute scale:MeasurementScale to Measure class
o This defines the scale of Measurement for measurements produced by the measure.

• Add named relation operation [0..1] from CollectiveMeasure to Operation
• Add constraint specify that either an Accumulator or an Operation, but not both should be specified for instances of CollectiveMeasure.
• Add documentation to clearly identify the defined uses of the NamedMeasure class.