All DICOM objects are defined by Information Object Definitions (IODs). See PS3.3. Representations of DICOM Resources are encodings of DICOM Information Objects into octet streams.

Each IOD has an associated set of Attributes, which define semantic concepts. Each Attribute has:

A Data Element is a concrete representation of an Attribute See PS3.5. Each Data Element has:

Each Instance contains Data Elements representing the Attributes from the Patient, Study, Series, and Instance levels of the IOD. For example, if a Series resource contains 12 Instances, then a transaction that retrieves that Series will contain a representation of the Series and its 12 Instances, in a specific media type, and each Instance will have Patient, Study, Series, and Instance level Attributes.

This Part of the Standard defines three distinct representations of DICOM Resources that can be encoded into DICOM Media Types: Instances, Metadata, and Bulkdata.

DICOM Media Types and their corresponding representations are defined in Section 8.7.3. Other media types used in this Part of the Standard are defined in Section 8.7.4.