6 DICOM Information Model
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# 6 DICOM Information Model

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.

## 6.1 Information Object Definition

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.

Figure 6-1. Major Structures of DICOM Information Model

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 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.

### 6.1.1 Composite IOD

A Composite IOD is an Information Object Definition that represents parts of several entities in the DICOM Model of the Real-World. (see PS3.3.) 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.

### Note

1. Actual communication of IOD Instances is via SOP Instances.

2. Whenever Composite SOP Instances are in fact related, some of the contextual information is redundant (i.e., the same information about the same Real-World Objects is contained in multiple SOP Instances).

The Composite IODs are specified in PS3.3.

### 6.1.2 Normalized IOD

A Normalized IOD is an Information Object Definition 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 PS3.3.

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