K.2.2 Attributes Definition
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### K.2.2 Attributes Definition

Attributes are defined for each entity in the internal Entity-Relationship Model. An Identifier in a C-FIND request shall contain values to be matched against the Attributes of the Entities in a Worklist Information Model. For any worklist request, the set of entities for which Attributes are returned, shall be determined by the set of Matching and Return Key Attributes specified in the Identifier.

#### K.2.2.1 Attribute Types

All Attributes of entities in a Worklist Information Model shall be specified both as a Matching Key Attribute (either required or optional) and as a Return Key Attribute.

##### K.2.2.1.1 Matching Key Attributes

The Matching Key Attributes are Keys, which select worklist items to be included in a requested Worklist.

###### K.2.2.1.1.1 Required Matching Key Attributes

A Basic Worklist Management SCP shall support matching based on values of all Required Matching Key Attributes of the C-FIND request. Multiple entities may match a given value for a Required Key.

If an SCP manages an entity with an unknown Attribute value (i.e., zero length), the unknown value shall fail to match any Matching Key value.

### Note

1. Even though there is no means to perform matching on such entities, they may be queried as a Return Key Attribute using a C-FIND request with a zero length value (universal match) or by a single wild card (wild card match).

2. An SCU may choose to supply any subset of Required Matching Key Attributes.

###### K.2.2.1.1.2 Optional Matching Key Attributes

In the Worklist Information Model, a set of Attributes may be defined as Optional Matching Key Attributes. Optional Matching Key Attributes contained in the Identifier of a C-FIND request may induce two different types of behavior depending on support for matching by the SCP. If the SCP

- does not support matching on the Optional Matching Key Attribute, then the Optional Matching Key Attribute shall be ignored for matching but shall be processed in the same manner as a Return Key Attribute.

- supports matching of the Optional Matching Key Attribute, then the Optional Matching Key Attribute shall be processed in the same manner as a Required Matching Key.

### Note

1. The Conformance Statement of the SCP lists the Optional Matching Key Attributes that are supported for matching.

2. An SCU can not expect the SCP to support a match on an Optional Matching Key.

##### K.2.2.1.2 Return Key Attributes

The values of Return Key Attributes to be retrieved with the Worklist are specified with zero-length (universal matching) in the C-FIND request. SCPs shall support Return Key Attributes defined by a Worklist Information Model according to the Data Element Type (1, 1C, 2, 2C, 3) as defined in PS3.5.

Every Matching Key Attribute shall also be considered as a Return Key Attribute. Therefore the C-FIND response shall contain in addition to the values of the requested Return Key Attributes the values of the requested Matching Key Attributes.

### Note

1. The Conformance Statement of the SCP lists the Return Key Attributes of Type 3, which are supported.

2. An SCU may choose to supply any subset of Return Key Attributes.

3. An SCU can not expect to receive any Type 3 Return Key Attributes.

4. Return Key Attributes with VR of SQ may be specified either with zero-length or with the zero-length item in the sequence.

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