A result shaping methodology is part of a bridge (translation layer) between an entity provider and an underlying store provider. The bridge accepts command trees and parameter values from a consumer (e.g., the entity provider), reshapes the trees as necessary for its underlying store provider to execute, executes resulting commands, and assembles the results from the commands into the nested data reader that the initial command tree requested. The result assembly advantageously takes a mapping declaration and compiles it into a set of expression definitions composed from a small number of simple functions. Each collection in the result has a corresponding expression describing how collection elements are realized given relational results. Other expressions describe boundary detection behavior. These expressions are compiled into functions used to shape relational data into arbitrary object graphs or streaming interfaces. Alternative versions of the expressions for performance or graceful contextual error handling are also compiled.