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Specification Test Nonconformity & Notes
Here we document any nonconformity in the specification tests.
Expression:
minimum Decimal
Expected result:
-99999999999999999999.99999999
Actual output:
-79228162514264337593543950335
Rationale:
Per the spec:
Note that if implementations support larger and/or more precise values than the minimum required precision and scale for Decimal, DateTime, and Time values, they will return the minimum representable decimal for the implementation.
Since the SDK uses the C# decimal type to represent the ELM System.Decimal type, we can represent smaller decimals than the minimum required by the specification.
Action:
Test skipped
Recommendation:
Change the expression in the test to be minimum Decimal <= -99999999999999999999.99999999 with an expected output of true
Expression:
maximum Decimal
Expected result:
99999999999999999999.99999999
Actual output:
79228162514264337593543950335
Rationale:
Per the spec:
Note that if implementations support larger and/or more precise values than the minimum required precision and scale for Decimal, DateTime, and Time values, they will return the minimum representable decimal for the implementation.
Since the SDK uses the C# decimal type to represent the ELM System.Decimal type, we can represent larger decimals than the maximum required by the specification.
Action:
Test skipped
Recommendation:
Change the expression in the test to be maximum Decimal >= 99999999999999999999.99999999 with an expected output of true
Expression:
1.0 'cm' * 2.0 'cm'
Expected result:
2.0'cm2'
Actual output:
Rationale:
Unit arithmetic is not yet supported. Quantities used in arithmetic expressions must have the default UCUM unit of 1.
Action:
Test skipped
Expression:
Power(2, -2)
Expected result:
0.25
Actual output:
0
Rationale:
As converted to ELM, the result type of this expression is defined to be System.Integer. Obeying this result type requires that we truncate from 0.25, the mathematically correct result, to 0.
Action:
Test skipped
Recommendation:
The spec discusses behavior for mixed argument types, but does not explicitly state that when Power is used with two Integer arguments that the result type should also be an Integer and decimal portions will be truncated. Given the behavior of the cql-to-elm reference implementation, that behavior is established. This contradicts the expected result of the test. Either the translator has to be updated to match the test, or the test should have an expected outcome of 0. In both cases, the spec should be updated to clarify this.
Expression:
Round(-0.5)
Expected result:
1.0
Actual output:
0
Rationale:
The spec uses the language "traditional round" to describe the rounding method. We use the default rounding strategy which is described in the language as "to nearest." For reference, .NET has devoted significant thought to this here.
This test contradicts the others when using the "to nearest" rounding.
Recommendation:
Clarify the rounding strategy, or fix the expected output of this test.
See Round0D5
See Multiply1CMBy2CM
Expression:
1'cm' ~ 0.01'm'
Expected result:
true
Actual output:
false
Rationale:
Quantity comparison of non-same units is not yet supported. Quantities used in comparison expressions must have the same unit.
Action:
Test skipped
See EquivEqCM1M01
Affected tests
- DateTimeDurationBetweenYear
- DateTimeDurationBetweenUncertainInterval
- DateTimeDurationBetweenUncertainInterval2
- DateTimeDurationBetweenUncertainAdd
- DateTimeDurationBetweenUncertainSubtract
- DateTimeDurationBetweenUncertainMultiply
- DateTimeDurationBetweenUncertainDiv
- DateTimeDurationBetweenMonthUncertain2
Example expression (DateTimeDurationBetweenYear):
years between DateTime(2005) and DateTime(2010)
Expected result:
Interval[4,5]
Actual output:
5
Rationale:
Per the spec:
The result of this operation is always an integer; any fractional periods are dropped.
Action:
Tests skipped
Recommendation:
Change the expected output of these tests to be a System.Integer, as indicated by the spec; alternatively, update the specification to be clear that the Duration operator returns an interval (to account for uncertainty), where certain results will be expressed as point intervals. The latter would be a breaking change and should be done with caution.
Example tests
- DateTimeAdd2YearsByDays
Recommendation:
Per the spec:
For partial date/time values where the time-valued quantity is more precise than the partial date/time, the operation is performed by converting the time-based quantity to the most precise value specified in first argument (truncating any resulting decimal portion) and then adding it to the first argument.
The method for converting 730 days to years would be to divide 730 by 365 days (or to multiply by 1/365). Floating point math computations can produce a value that is not exactly 2.0 but is rather something like 1.99999999986. In this case, if the implementation truncates the decimal portion after the imprecise floating point mathematics, it could result in 1 year instead of 2, as expected by the test (DateTime(2014) + 730 days = @2016).
This SDK rounds all conversions to a precision of 8 decimal places, which will round the imprecise sub-2.0 floating point value to 2.0, thus satisfying this test.
Our recommendation is to update the spec to formalize this rounding process.