Product documentation
Abstract
IBM Cognos Dynamic Cubes and IBM Cognos Transformer are generally consistent in the resolution of relative time members. There are some cases in which they differ, for example when a week level exists in a Gregorian calendar hierarchy.
Content
IBM Cognos Dynamic Cubes and IBM Cognos Transformer are generally consistent in the resolution of relative time members.
There are some cases in which they differ, for example when a week level exists in a Gregorian calendar hierarchy.
Cognos Dynamic Cubes resolves custom and autogenerated relative time members using an approach similar to the parallelperiod function, i.e. locate a member in the same relative position.
When the parallel period has fewer members than the current period, the last member of the parallel period is returned. For example, 'Same Day, Prior Month' will return Apr 30, when the current day is May 31. The parallelperiod approach is applied consistently regardless of hierarchy calendar type or level types.
Dynamic Cubes resolves differently than PowerPlay Transformer in the following cases:
 Gregorian calendar when context period is year, target period is day, and current day is a leap day.

Suppose a hierarchy has Year/Quarter/Month/Day levels, and the current day is 'Feb 29, 2012'. A member defined as 'same day prior year' returns 'Mar 1, 2011' in Transformer, whereas Dynamic Cubes returns 'Feb 28, 2011'.
Transformer applies an offset of 29 from the beginning of Feb in 2011, which resolves to the first day of March.
Dynamic cubes cannot find a member in the same relative position because Feb only has 28 days in the prior year, so it returns the last member.
 Gregorian calendar when context period is quarter, and target period is day.

Suppose a hierarchy has Year/Quarter/Month/Day levels, and the current day is 'May 31, 2013'. A member defined as 'same day prior quarter' returns 'Mar 2, 2013' in Transformer, whereas Dynamic Cubes returns 'Feb 28, 2013'.
Transformer locates the day member at the same offset from the beginning of the context period. The current day is at offset 61 from the beginning of the 2nd quarter, and the day at offset 61 from the beginning of the 1st quarter is Mar 2. If the offset were to exceed the number of days in the context period, the last day in context would be returned.
Dynamic cubes cannot find a member in the same relative position because Feb only has 28 days, so it returns the last member.
 Gregorian calendar with a week level.

A typical hierarchy may have YearQuarterMonthWeekDay levels. Unlike a Retail calendar which is organized with a symmetrical hierarchical structure, the Gregorian hierarchy with weeks is physically asymmetrical at the week and day levels. Some months have 5 weeks while others have 6. The number of days in the first and last week of different months varies between 1 and 7. Some weeks are split across month boundaries.
 For 'same day prior week', Transformer returns the same weekday in the prior logical week, regardless of relative position. So if the current day is a Saturday, the Saturday of the prior week is returned, even if it happens to be in the prior month.
Suppose the current day is 'Saturday Jan 5, 2013'. For 'same day prior week' Transformer returns 'Saturday Dec 29, 2012', whereas Dynamic Cubes returns 'Monday Dec 31, 2012'. There are only 2 days in the prior relative week (Dec 30 and 31), so Dynamic Cubes returns the last day. When the context period is higher than the week level, such as 'same day prior year', Transformer returns the day at the same relative offset from the beginning of the prior year, effectively ignoring the week level. Dynamic Cubes uses relative positioning at each level of the hierarchy.
 In Transformer, when the target period is week, the week at the same logical offset from the beginning of the context period is returned, where a week is a Sunday to Saturday time period. The physical hierarchy structure is ignored, and if the logical week spans a month boundary, Transformer returns the two corresponding week members. Dynamic cubes returns a week in the same relative position based on the physical hierarchy structure.
Suppose the current day is 'Jan 31, 2011 (week 6)'. Note this week is split across Jan and Feb. For 'same week, prior month', Transformer returns two members, one corresponding to week 5 of Dec 2010 which runs Sunday to Friday, and week 1 of Jan 2011, which has one day, Sunday. Dynamic cubes returns week 5 of Dec 2010  Dec does not have a week at ordinal 6, so the last week is returned.
Transformer uses its knowledge of the number of weeks in a month, or days in a week, to locate members in prior/next periods. Transformer also treats a week as a logical 7 day period, typically from Sunday to Saturday. As stated above, Dynamic Cubes attempts to find a member in the same relative position in a prior/next context period similar to the parallelperiod function. In general, the results between Transformer and Dynamic Cubes differ when the target period is day or week, for higher level context periods.

Suppose the current day is 'Jan 7, 2012', which is in week 1 of 2012. For 'same day prior year', Transformer returns 'Jan 7, 2011', which is in week 2 of 2011. Dynamic Cubes returns 'Jan 1, 2011', which is the only day in week 1 of 2011. A day at ordinal 7 of week 1 in 2011 doesn't exist, so the last day of week 1 is returned.
 Retail/Lunar calendar when the context period is month and the target period is day or week.
Consider a Retail calendar hierarchy with levels YearSeasonMonthWeekDay. Months are structured using a repeating 454 week pattern, i.e. Jan(4)Feb(5)Mar(4)Apr(4)May(5)Jun(4) etc. Every week has 7 days. The hierarchy is uniform except days and weeks within a month.
Transformer handles daily and weekly monthovermonth comparisons by applying an offset from the beginning of the month. Dynamic Cubes, as in all scenarios, uses a parallel period approach, returning a member in the same relative position.
Suppose the current month has 5 weeks and the current day is day 35. For 'same day prior month', Transformer applies an offset of 35 from the start of the prior month which has 28 days, and thus resolves to day 7 of the current month. Dynamic Cubes attempts to find a member at ordinal 35 of the prior month which doesn't exist, so it resolves to day 28 which is the last day of the prior month.