The Attributes of an IOD describe the properties of a Real-World Object Instance. Related Attributes are grouped into Modules which represent a higher level of semantics documented in the Module Specifications found in Annex C in PS 3.3 of the DICOM Standard.
Attributes are encoded as Data Elements using the rules, the Value Representation and the Value Multiplicity concepts specified in PS 3.5 of the DICOM Standard. For specific Data Elements, the Value Representation and Value Multiplicity are specified in the Data Dictionary in PS 3.6 of the DICOM Standard.
When multiple modules containing the same Attributes(s) are included in an IOD, the Attribute shall be encoded only once into a Data Element. If one of the modules is a specialization of the other (e.g., General Image and CT Image) the Attribute definition contained in the more specialized module shall be used.