ISO/IEC 15476-3:2006 explains the Data definitions subject area of the CDIF semantic metamodel, that defines the primitive data types and the objects which are used for structured data. The CDIF semantic metamodel is used to ensure that the information transferred by tools communicating using CDIF is expressed with an agreed meaning. This subject area contains meta-objects that are used as the basis of the data components of other subject area standards, and also meta-relationships and meta-attributes that are applicable to all data-related meta-objects. ISO/IEC 15476-3:2006 is intended to be used by anyone wishing to understand and/or use CDIF. It provides a definition of a single subject area of the CDIF semantic metamodel. It is suitable for: Those evaluating CDIF; Those who wish to understand the principles and concepts of a CDIF transfer; and Those developing importers and exporters.