3 Definitions
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# 3 Definitions

Attribute

  A property of an Information Object. An Attribute has a name and a value that are independent of any encoding scheme.

Command

  A request to operate on information across a network.

Command Element

  An encoding of a parameter of a command that conveys this parameter's value.

Command Stream

  The result of encoding a set of DICOM Command Elements using the DICOM encoding scheme.

Conformance Statement

  A formal statement that describes a specific product implementation that uses the DICOM Standard. It specifies the Service Classes, Information Objects, and Communication Protocols supported by the implementation.

Data Dictionary

  A registry of DICOM Data Elements that assigns a unique tag, a name, value characteristics, and semantics to each Data Element.

Data Element

  A unit of information as defined by a single entry in the data dictionary.

Data Set

  Exchanged information consisting of a structured set of Attributes. The value of each Attribute in a Data Set is expressed as a Data Element.

Data Stream

  The result of encoding a Data Set using the DICOM encoding scheme (Data Element Numbers and representations as specified by the Data Dictionary).

Information Object

  An abstraction of a real information entity (e.g., CT Image, Structured Report, etc.) that is acted upon by one or more DICOM Commands.

  ### Note

  This term is primarily used in PS3.1, with a few references in PS3.3. It is an informal term corresponding to a formal term that is introduced in PS3.3. In all other parts of the DICOM Standard this formal term is known as an Information Object Definition.

Information Object Class

  A formal description of an Information Object, which includes a description of its purpose and the Attributes it possesses. It does not include values for these attributes.

  ### Note

  This term is only used in PS3.1. It is an informal term corresponding to a formal term that is introduced in PS3.4. This formal term is known as a Service-Object Pair Class or more commonly as a SOP Class.

Information Object Instance

  A representation of an occurence of an real-world entity, which includes values for the Attributes of the Information Object Class to which the entity belongs.

  ### Note

  This term is only used in PS3.1. It is an informal term corresponding to a formal term that is introduced in PS3.4. This formal term is known as a Service-Object Pair Instance or more commonly as a SOP Instance.

Message

  A data unit of the Message Exchange Protocol exchanged between two cooperating DICOM Applications. A Message is composed of a Command Stream followed by an optional Data Stream.

Service Class

  A structured description of a service that is supported by cooperating DICOM Applications using specific DICOM Commands acting on a specific class of Information Object.

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