Techniques for validating complex digital objects such as DICOM objects. The techniques employ a declarative validation document which employs a declarative constraint language to specify the constraints to which the complex digital object is subject. A validator performs an evaluation of the constraint document with regard to the complex digital object. The complex digital object is valid if all of the constraints in the validation document are satisfied. The constraint document may be compiled by an optimizing compiler and the validator may apply the resulting compiled constraint specification to an in-memory representation of the digital object which has been optimized for fast reference. An example is given of the use of the techniques with DICOM objects.