it is for upgrading the feature definitions between releases... say you've moved from R22 to R26, DS might have done something to the definition of features (split seems to have been tampered with...) opening an old file (from R22) in the new release (R26) will not change any of the old definitions (they are still those of R22) BUT if you right klick on the Upgrade, then the feature will be recomputed to the new definition...