The DICOM Information Model defines the structure and organization of the information related to the communication of medical images. Figure 6-1 shows the relationships between the major structures of the DICOM Information Model.
An Information Object Definition (IOD) is an object-oriented abstract data model used to specify information about Real-World Objects. An IOD provides communicating Application Entities with a common view of the information to be exchanged.
An IOD does not represent a specific Instance of a Real-World Object, but rather a class of Real-World Objects that share the same properties. An IOD used to generally represent a single class of Real-World Objects is called a Normalized Information Object. An IOD that includes information about related Real-World Objects is called a Composite Information Object.
A Composite IOD is an IOD that represents parts of several entities included in the DICOM Model of the Real World. This Model is introduced in Section 7. Such an IOD includes Attributes that are not inherent in the Real-World Object that the IOD represents but rather are inherent in related Real-World Objects.
These related Real-World Objects provide a complete context for the exchanged information. When an Instance of a Composite IOD is communicated, this entire context is exchanged between Application Entities. Relationships between Composite IOD Instances shall be conveyed in this contextual information.
The Composite IODs are specified in Annex A.
A Normalized IOD is an IOD that generally represents a single entity in the DICOM Model of the Real World.
When an Instance of a Normalized IOD is communicated, the context for that Instance is not actually exchanged. Instead, the context is provided through the use of pointers to related Normalized IOD Instances.
The Normalized IODs are specified in Annex B.