Time periods, such as Month to Date, Quarter to Date, Previous N Year to Date, Trailing N Months, and Trailing N Periods, are calculated using the year, month, and day parts of a reference date. For example, Month to Date covers the period starting at the beginning of the reference date’s month and ending at the reference date. If the reference date is 2012-01-08, the period is 2012-01-01 to 2012-01-08. Contrast this with Current Month, which is calculated using only the year and month parts of a reference date. For a reference date of 2012-01-08, Current Month covers the entire month, 2012-01-01 to 2012-01-31.
Because the * to Date and Trailing N * time periods use the day part of a reference date, the time dimension defined in the cube must include the Day Of Year level. Figure 21-10 shows an example in which the time levels, Year, Quarter, Month, and Day Of Year, are selected for a time dimension.
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Figure 21-10
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If the time dimension in the cube does not include the Day of Year level, and you use a * to Date or a Trailing N * time period in a relative time period measure, BIRT displays a warning when you run the report. In the generated report, those measures display the wrong results. Month to Date returns the same results as Current Month, Quarter to Date returns the same results as Current Quarter, and so on. In other words, the day part of the reference date has no effect.
