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.
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.
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.
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.
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.
Both the C-FIND request and response contain an Identifier encoded as a Data Set (see PS 3.5).
An Identifier in a C-FIND request shall contain:
Key Attributes values to be matched against the values of Attributes specified in the SOP Class identified by the Affected SOP Class UID.
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 Request Identifier. It shall not be included otherwise.
Conditionally, the Attribute Timezone Offset From UTC (0008,0201). This Attribute shall be included if Key Attributes of time 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 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.
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:
Key Attributes with values corresponding to Key Attributes contained in the Identifier of the request (Key Attributes as defined in CC.2.5-3.)
— 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.
All C-FIND SCUs shall be capable of generating query requests that meet the requirements of the “Worklist” Search Method (see CC.184.108.40.206).
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 requests that the SCP perform a match of all keys specified in the Identifier of the request against the information it possesses of the Query specified in the request.
The SCU shall interpret Pending responses to convey the Attributes of a match of an item.
The SCU shall interpret a response with a status equal to Success, Failure, or Cancel to convey the end of Pending 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.
All C-FIND SCPs shall be capable of processing queries that meet the requirements of the “Worklist” Search (see CC.220.127.116.11). 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:
The SCP is requested to perform a match of all the keys specified in the Identifier of the request, against the information it possesses. Attribute matching is performed using the key values specified in the Identifier of the C-FIND request as defined in Table CC.2.5-3.
The SCP generates a C-FIND response for each match using the "Worklist" Search method. All such responses shall contain an Identifier whose Attributes contain values from a single match. All such responses shall contain a status of Pending.
— 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.
The following steps are used to generate match responses.
Match the key match attributes contained in the Identifier of the C-FIND request against the values of the Key Attributes for each worklist entity.
If there are no matching keys, then there are no matches, return a response with a status equal to Success and with no Identifier.
For each entity for which the Attributes match all of the specified matching key attributes, construct an Identifier. This Identifier shall contain all of the values of the Attributes for this entity that correspond to the return keys specified in the C-FIND request.
Return a response for each remaining Identifier.
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.
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).