The Alternate dictionary contains classes that describe sets of data values which are interchangeable with each other. The Alternate_Values describes a direct one-to-one relationship of arrays of data values. Each data array must have the same dimensionality and number of elements. The Data_Values class describes the values stored in a data array. The Local_Internal_Reference class is used to cross-reference other classes or objects within the product. This section contains the simpleTypes that provide more constraints than those at the base data type level. The simpleTypes defined here build on the base data types. This is another component of the common dictionary and therefore falls within the pds namespace. The local_reference_type attribute provides the name of an association between an entity identified by a local_identifier_reference and another corresponding entity identified by a local_identifier