Steven C. Horii, MD

Association
A communication connection established between two DICOM applications by which DICOM information is exchanged. A device may support one or more associations simultaneously.

Attributes
Items that describe something. In object-oriented analysis, part of the process is determining what attributes of an entity are needed to describe or identify it. In DICOM, attributes are used to describe information objects.

Composite objects
Those objects defined in DICOM that correspond to multiple entities or parts of multiple entities in the E-R model.

Data elements
Instances (real-world value assigned) of the descriptive attributes that provide the characteristics of entities in the E-R model. The term data element is used to describe the contents of data sets.

Data set
In DICOM, an information object in which real-world values have been provided for all attributes, which thus become data elements. Entity-relationship (E-R) model.-A formal description of entities (eg, patients, equipment, images) and how they are related from an information organization perspective.

Explicit VR
A method of including the VR of an attribute in the attribute itself.

Implicit VR
The ACR-NEMA method of defining the VR of an attribute in the data dictionary.

Information object instance
An information object to whose attributes real-world values have been assigned.

Information objects
In DICOM, objects such as images, reports, and patients whose function is to carry information; entities in an E-R model whose descriptive attributes have been listed and defined.

Layer
A set of software or hardware that performs specific functions needed for the communications process.

Normalized objects
Those objects defined in DICOM that correspond to a single entity in the E-R model.

Object-oriented analysis
The process of determining the object (or E-R) model that describes a particular activity.

Packet
A small (usually) portion of a larger message that is being communicated. In addition to the message fragment, the packet has header information that allows it to be sent to the correct location and to be put in correct order should the multiple packets of a message arrive out of sequence. The packet also usually contains information that allows a communication system to determine if it got corrupted on the way to its destination.

Protocol
The set of rules that allows two devices to communicate. In layered communications designs, peer-to-peer communication (wherein a layer in one device communicates with the corresponding layer in another) is described by protocols.

Service
A set of functions performed to communicate between layers within a device.

Stack
A set of layers designed to provide communications services to applications.

Tag
In DICOM, the numeric name of an attribute or data element.

Transfer syntax
In DICOM, a formal description of the manner in which the VR of data elements is presented and their encoding (byte order and compression type, if used) is performed.

Unique identifier
A specific numeric construct used when an entity is referenced. It can be thought of as a unique name that will allow the desired entity to be found, retrieved, and distinguished from other entities.

Value representation (VR)
In DICOM, the description of how the attribute value is represented (eg, text, binary data, patient name).

ABBREVIATIONS

ACR-NEMA = American College of Radiology-National Electrical Manufacturers' Association

DICOM = Digital Imaging and Communications in Medicine

DIMSE = DICOM message service element

E-R = entity-relationship

ISO-OSI = International Standards Organization Open Systems Interconnection

SNOMED = Systematized Nomenclature for Medicine

SOP = service-object pair

UID = unique identifier

VR = value representation

RadioGraphics 1997; 17:1297-1309
©RSNA, 1997

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