An efficient, logical and expressive type system is provided for flexibly defining types of a declarative programming language so that efficient and structurally compact data intensive applications can be generated. The type system supports the combination of refinement types and type membership expressions, as well as a top type that encompasses all valid values as members. With the type system, types can be expressed as intersections and/or unions of other types. Thus, types can be efficiently represented for a full range of types of data as may be found in real world data stores.