Constrain Transmission Wrapper

Issue Statement and Criteria Definition

There are several crucial issues in the current Wrapper model, that are of interest and in the scope of the MCCI R2 project. These can be summarized as follows:

• The current message and transmission layer seems to mix transmission and "how to interpret/process" information. This causes confusion and ambiguity in HL7 implementations
• Transmission Wrapper (MCCI R1) provides various constructs available in the MIL technologies, such as reliable messaging, addressing, attachments handling, sequencing and security. This causes problems in implementations relying on MIL to provide these QoS data communication features.

Our aim is to analyze the classes and atributes contained in Transmission Wrapper, but also look into ControlAct when necessary, and determine should they go into the Transmission Part of the Behavioral Contract Wrapper (purely transmission oriented semantics), or should they belong to Conversation Part (payload and context related semantics). The following criteria are used to determine if an attribute is Transmission or Processing related:

• The class/attribute is related to processing if it has an impact on the semantic interpretation of the interaction
  • Action - these constructs should belong to Conversation Part
• The attribute is related to processing if the attribute is processed by the receiving HL7 Application as opposed to the Messaging Adapter.
  • Action - these constructs should belong to Conversation Part
• The attribute is related to Transmission if there is equivalent functionality in MIL headers (e.g. Webservices, ebXML, SOAP).
  • Action - these constucts should belong to Transmission Part

(Miroslav) The list below is just a start and needs more work...

A list of "pure transmission" classes and attributes includes:

• Message.id attribute: id of the Transmission
• Message.creationTime attribute: time of the transmission
• AttentionLine Keyword/value attribute: Transmission routing information
• Message.securityText: use is transmission oriented.
• Accept Ack class: Reliable messaging on the HL7 layer
• Attachment class: Attachment handling on the HL7 layer
• Sender/Receiver/Device classes: Addressing on the HL7 layer
• Message.sequenceNumber: inOrder delivery on the HL7 layer

A list of "processing related attributes" includes:

• Message.profileId - Indicates how to validate the instance. Can influence receiver behavior. Identifies part of the "contract" between sender and receiver.
• Transmission.versionCode - Indicates how to validate the interactions, allows confirmation of "can I process this?". Identifies part of the "contract" between sender and receiver.
• Transmission.interactionId - Indicates how to validate the interaction, allows confirmation of "can I process this?" and determines receiver behavior. Identifies part of the "contract" between sender and receiver.
• Transmission.processingModeCode - Indicates how the instance is to be treated. Identifies part of the "contract" between sender and receiver.
• Message.processingCode - Indicates how the instance is to be treated. Identifies part of the "contract" between sender and receiver.

Notes related to MCCI R1 wrappers:

• Message.attachmentText (deprecated) - Contains information referenced by the message
• Note that agent/Organization and LocatedEntity/Place have been removed from the R-MIM during the May 2006 INM out of cycle meeting.

Comments

Comment 12/18/06 (Alan Honey) - As I look at some of these items, in my mind this still leaves unresolved some higher level questions, namely what is requirement and what is solution, and also what is appropriately "instance level" vs "contractual. Some of the items identified above are (correctly in my view) identified as "contractual" yet the need is felt for instance level attributes, which is a messaging specific solution. If they are totally optional items, then I can live with that. Going back to the SOA vs Messaging issue, in SOA, most of this variability would be constrained in the contract exposed by a specific version of a specific service, and a specific endpoint would be identified that exposed the specific version, and some would be handled by process management (orchestration) mechanisms totally without any action by either provider or consumer. What I am saying is that the "requirement" for the items defined as "processing" is not "paradigm or transport" specific, but the solution maybe. In the case of SOA, some of these would not require any specific instance level attributes at all.

Comment 01/09/07 (Miroslav) - I think we should separate the items that refer to HL7 protocol semantics (i.e. renaming the "pure transmission" group) from the HL7 message processing related attributes. The HL7 communication protocol semantics would encompass items that describe the HL7 Transmission Pattern as the core unit of HL7 communication protocol. For example, Message.acceptAck is pure HL7 protocol semantics, and expresses the requirement for the Receiver to send the Message Adapter Acknowledgement (MCCI_IN002002), which is an HL7 message and not MIL specific interaction. The idea is to have items grouped in two categories, so the HL7 protocol semantics can be (in future) declared as an optional (part of the) wrapper (See Behavioral Contract Wrapper (new wrapper mechanism)), since these requirements are nowadays are usually managed and implemented with different MIL technologies. We should have that machinery in the HL7 messages as well (for reasons such as backwards compatibility, simple and pure messaging architectures, etc), but those would all need to be optional as Alan suggests.

Possible solutions

1. Moving some/all of these attributes to ControlAct (which would actually have to be a deprecate and copy)

• Advantages - ControlAct is already understood and in place
• Disadvantages - This information relates to the Interaction, while ControlAct really Describes the trigger event. Also, ControlAct is used to convey history, where these attributes aren't terribly relevant

2. Adding an additional class to deal with this information. See Behavioral Contract Wrapper (new wrapper mechanism), which adds an Act to the current ControlAct wrapper.

• Advantages - Addresses disadvantages above
• Disadvantages - It adds yet another layer

OPEN ISSUE: MnM and INM to express a preference for one of the above options (regardless of which specific attributes will be "moved").

Discussion

In application responses, it would make sense to include a link to the original controlAct, instead of including a reference to the orginal Transmission. (Tom de Jong, 20051113)

20060630 MnM discussion

• need a better explanation of why the layers should be separated
  • Need to indicate what can be thrown away and what can't
  • Need to indicate what can be changed when routing and what can't
  • Better mapping to "standard" transports
• need to recognize that this "non-transport" information is routing related
• Ask INM and SOA to update this
• Defer future discussion until INM asks us to re-address
• Consider as an agenda item INM/MNM joint meeting Sept. 2006

Resolution

MnM endorsed option #2 at the January, 2007 WGM