CC.2.8 Search for Unified Procedure Step (C-FIND)

This operation allows an SCU to locate and get information about Unified Procedure Step instances of interest that are managed by an SCP. This operation shall be invoked by the SCU through the DIMSE C-FIND Service. The SCP processes such queries, matches UPS instances it manages against the keys present in the Identifier and returns C-FIND responses.

The SCU might be searching for UPS instance with the intention of starting work on one of them or perhaps with the intention of subscribing to monitor the progress of an instance.

CC.2.8.1 Operation

CC.2.8.1.1 E/R Model

In response to a given C-FIND request, the SCP might send several C-FIND responses, (i.e. one C-FIND response per matching worklist item). Each worklist item describes a single task and its related information.

The Unified Procedure Step Query Information Model is represented by the Entity Relationship diagram shown in Figure CC.2.8-1.

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Figure CC.2.8-1 Unified Procedure Step E-R Diagram

There is only one Information Entity in the model, which is the Unified Procedure Step. The attributes of a Unified Procedure Step can be found in Table CC.2.5-3.

CC.2.8.1.2 C-FIND Service Parameters

CC.2.8.1.2.1 SOP Class UID

The Affected SOP Class UID of the C-FIND DIMSE request shall always be the UPS SOP Class negotiated for the Presentation Context under which the service is requested. This will always be either the UPS Pull SOP Class or the UPS Watch SOP Class. See CC.3.1 for further details.

For both the UPS Pull SOP Class and the UPS Watch SOP Class, the C-FIND is performed against the Unified Procedure Step Information Model shown in CC.2.8-1.

CC.2.8.1.2.2 Priority

The Priority Attribute defines the requested priority of the C-FIND operation with respect to other DIMSE operations being performed by the same SCP.

Processing of priority requests is not required of SCPs. Whether or not an SCP supports priority processing and the meaning of the different priority levels shall be stated in the Conformance Statement of the SCP.

CC.2.8.1.3 Identifier

Both the C-FIND request and response contain an Identifier encoded as a Data Set (see PS 3.5).

CC.2.8.1.3.1 Request Identifier Structure

An Identifier in a C-FIND request shall contain:

Note: This means that Specific Character Set (0008,0005) is included if the SCU supports expanded or replacement character sets in the context of this service. It will not be included if expanded or replacement character sets are not supported by the SCU.

The Key Attributes and values allowable for the query shall be defined in the SOP Class definition corresponding to the Affected SOP Class UID for the corresponding Unified Worklist And Procedure Step Information Model.

CC.2.8.1.3.2 Response Identifier Structure

The C-FIND response shall not contain Attributes that were not in the request or specified in this section.

An Identifier in a C-FIND response shall contain:

— Conditionally, the Attribute Specific Character Set (0008,0005). This Attribute shall be included if expanded or replacement character sets may be used in any of the Attributes in the Response Identifier. It shall not be included otherwise. The C-FIND SCP is not required to return responses in the Specific Character Set requested by the SCU if that character set is not supported by the SCP. The SCP may return responses with a different Specific Character Set.

— Conditionally, the Attribute Timezone Offset From UTC (0008,0201). This Attribute shall be included if any Attributes of time in the Response Identifier are to be interpreted explicitly in the designated local time zone. It shall not be present otherwise, i.e., it shall not be sent with a zero-length value.

Note: This means that Specific Character Set (0008,0005) is included if the SCP supports expanded or replacement character sets in the context of this service. It will not be included if expanded or replacement character sets are not supported by the SCP.

CC.2.8.2 Service Class User Behavior

All C-FIND SCUs shall be capable of generating query requests that meet the requirements of the “Worklist” Search Method (see CC.2.8.3.1).

Required Keys and Optional Keys, identified in Table CC.2.5-3, associated with the Query may be contained in the Identifier.

An SCU conveys the following semantics using the C-FIND requests and responses:

— The SCU shall interpret a Failure response to a C-FIND request as an indication that the SCP is unable to process the request.

— The SCU may cancel the C-FIND service by issuing a C-FIND-CANCEL request at any time during the processing of the C-FIND. The SCU shall recognize a status of Cancel to indicate that the C-FIND-CANCEL was successful.

CC.2.8.3 Service Class Provider Behavior

All C-FIND SCPs shall be capable of processing queries that meet the requirements of the “Worklist” Search (see CC.2.8.3.1). This does not imply that an SCP which supports the UPS Watch SOP Class must also be an SCP of the UPS Pull SOP Class.

The SCP shall support attribute matching as described in Section C.2.2.2.

An SCP conveys the following semantics using the C-FIND requests and responses:

— When all matches have been sent, the SCP generates a C-FIND response which contains a status of Success. A status of Success shall indicate that a response has been sent for each match known to the SCP.

Notes: 1. No Identifier is contained in a response with a status of Success. For a complete definition, see PS 3.7.

2. When there are no matches, then no responses with a status of Pending are sent, only a single response with a status of Success.

— The SCP shall generate a response with a status of Failure if it is unable to process the request. A Failure response shall contain no Identifier.

— If the SCP receives C-FIND-CANCEL indication before it has completed the processing of the matches it shall interrupt the matching process and return a status of Cancel.

Bi-directional Authentication of machines/users/applications is possible at association time (see PS 3.7 and PS 3.15). PS 3.7 provides a “Refused: Not Authorized” error code. Further requiring or documenting authentication and/or authorization features from the SCU or SCP is beyond the scope of this SOP Class.

CC.2.8.3.1 Worklist Search Method

The following steps are used to generate match responses.

Table CC.2.5-3 defines the Attributes of the Unified Procedure Step Information Model, the requirements for key matching, and the requirements for return keys.

CC.2.8.4 Status Codes

Table CC.2.8-2 defines the status code values that might be returned in a C-FIND response. Fields related to status code values are defined in PS 3.7.

Table CC.2.8-2C-FIND RESPONSE STATUS VALUES

Service Status Further Meaning Status Codes Related Fields
Failure Refused: Out of Resources A700 (0000,0902)
Identifier Does Not Match SOP Class A900 (0000,0901) (0000,0902)
SOP Class not Supported 0122H
Unable to process (any value C000 through CFFF as assigned by the implementation) (0000,0901) (0000,0902)
Cancel Matching terminated due to Cancel request FE00 None
Success Matching is complete - No final Identifier is supplied. 0000 None
Pending Matches are continuing - Current Match is supplied and any Optional Keys were supported in the same manner as Required Keys. FF00 Identifier
Matches are continuing - Warning that one or more Optional Keys were not supported for existence for this Identifier. FF01 Identifier

Note: Status Codes are returned in DIMSE response messages (See PS 3.7). The code values stated in column "Status Codes" are returned in Status Command Element (0000,0900).