The Multi dictionary contains classes that describe the composition of multidimensional data consisting of Array (and Array subclass) data objects. It provides a way to associated data objects and align the objects in general multi-dimensional structures. The Aligned_Values class describes the values which align element-by-element with the elements of a observation data array. The aligned values array must have the same dimensions as the observation array. The Axis_Values class describes the values which are associated with the elements along an axis of a observation data array. The Face_Plane class describes a plane which is defined by two axes. The Face_Values class describes the values which are associated with the elements on the face of a observation data array. The Local_Internal_Reference class is used to cross-reference other classes or objects within the product. The Particle_Observation describes the data of a observation and the values which are associated with the elements along an axis or on the face of a observation data array. The Primary_Values class describes the values which are the primary observation data array. 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 index of the axis. The first axis is numbered as 1. The axis number that defines one axis of a face plane. 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