A Datamart stores time dimensions (week, month, quarter and year) for the pricing dates. To get a time dimension value, a DMCalendar instance (Datamart Calendar) can be used.
For example, the date "2018-01-24" falls in the week "2018-W04"; which can be retrieved by the getWeek(date) method of a DMCalendar instance:
Similarly, other time dimensions such as Month, Quarter and Year can be retrieved by getMonth(date), getQuarter(date) and getYear(date) methods respectively.
These functions (getWeek(), ...) are always returning values from Gregorian calendar and always formatted in the default built-in way. In other words, it does NOT use data from cal data source. If you need the actual data from cal table, you need to make a query to that data source.