Preferences in the scope of relational databases allow modeling user wishes by queries with soft constraints. There are different frameworks for database preferences including commercially available systems. They slightly vary in semantics and expressiveness but have in common that preferences induce strict partial orders on a given data set. In the present paper we study the expressiveness of preference operators in the available implementations. Particularly, we search for decompositions of strict partial orders into fundamental preference constructs. We study which preference operators and operands are necessary to express any strict partial order. Finally, we present two decomposition algorithms and show their correctness.