The data source supplies the starting instances; the primary business object describes those instances. All Workers returns current, former and future Worker instances. Workers for HCM Reporting with the All Active Workers source filter returns the current employed population. All Positions returns staffing slots. Job Applications returns Job Application instances. Several applications can relate to one position, and one person can submit several applications.
Pick the grain before writing a filter. A report on candidates can't count vacancies by counting its rows, and an active-only worker source can't produce an exit roster for people it has already removed. Related fields let you show a linked object's values, but they don't change the report's grain. Check a known boundary record when the request uses an as-of date or includes former workers.