7.4 Data Element Type
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## 7.4 Data Element Type

An attribute, encoded as a Data Element, may or may not be required in a Data Set, depending on that Attribute's Data Element Type.

The Data Element Type of an Attribute of an Information Object Definition or an Attribute of a SOP Class Definition is used to specify whether that Attribute is mandatory or optional. The Data Element Type also indicates if an Attribute is conditional (only mandatory under certain conditions). The Data Element Types of Attributes of Composite IODs are specified in PS3.3. The Data Element Types of Attributes of Normalized IODs are specified as Attributes of SOP Classes in PS3.4.

### 7.4.1 Type 1 Required Data Elements

IODs and SOP Classes define Type 1 Data Elements that shall be included and are mandatory elements. The Value Field shall contain valid data as defined by the elements VR and VM as specified in PS3.6. The Length of the Value Field shall not be zero. Absence of a valid Value in a Type 1 Data Element is a protocol violation.

### Note

1. For data elements with a string (CS, SH, LO) rather than binary, text or sequence Value Representation, and for which multiple Values are allowed, the presence of a single Value is sufficient to satisfy the Type 1 requirement, unless specified otherwise in the Attribute description, and other Values may be empty, unless otherwise specified by the IOD. The presence of one or more delimiter (BACKSLASH) characters alone, without any Values, is not sufficient to satisfy the Type 1 requirement, since even though the Value Length is greater than zero, there is no valid Value present.

2. A Type 1 Sequence Data Element will contain one or more Items, as defined by the IOD (irrespective of the VM of the Sequence, which is always one (Section 7.5)). Whether or not those Items may be empty (contain no Data Elements) depends on the IOD definition of the Data Set for each Item.

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