Rules may only use fields that physically store their value in the database or use the special values as specified above. They will not work with computed fields from the data dictionary. For example, you cannot create a rule that uses fields such as DATE_CLOSED_SINCE, DATE_CREATED_DAY, DATE_CREATED_MONTH, DATE_CREATED_WEEK, DATE_CREATED_TRUNC, DATE_CREATED_YEAR, DATE_LAST_STATUS_CHANGED_SINCE, DAYS_IN_STATUS, DAYS_OPEN, MONTHS_OPEN, WEEKS_OPEN, TIMESTAMP_MONTH, TIMESTAMP_SINCE, TIMESTAMP_TRUNC, TIMESTAMP_WEEK, TIMESTAMP_YEAR, WEEKS_IN_STATUS, WEEKS_OPEN, or any field with a display type of Label or Custom.
However, you can often provide your own expression in a rule to derive the same information. For example, to calculate the number of days since the creation of an issue you may create a field named MY_DAYS_OPEN with a display type of Number and then construct a rule such as:
MY_DAYS_OPEN = (SYSDATE - DATE_CREATED);
