HOL-OCL defines a machine-checked *formalization of the semantics *as described in the standard for OCL 2.0. This conservative, shallow embedding of UML/OCL into Isabelle/HOL includes support for typed, extensible UML data models supporting inheritance and subtyping inside the typed λ-calculus with parametric polymorphism. As a consequence of conservativity with respect to higher-order logic (HOL), we can guarantee the consistency of the semantic model. Moreover, HOL-OCL provides several derived calculi for UML/OCL that allows for formal derivations establishing the validity of UML/OCL formulae. Automated support for such proofs is also provided.