Complex sentence: Doll offers an example of such a curriculum with his 4Rs (Richness, Relations, Recursion, and Rigor), which is viewed as an alternative to Tyler's rationale.
Split into simpler sentences: Doll offers an example of such a curriculum with his 4Rs (Richness, Relations, Recursion, and Rigor). Doll's 4Rs is viewed as an alternative to Tyler's rationale.