Acknowledgements in HL7V2.x

HL7V2.x messaging standard indicates that Acknowledgements (ACK’s) are messages sent by a receiving system to the sending system in response to a transaction from the sending application. In a setup where HL7 is implemented the sending system will assume that the message sent by it is not received till it receives an ACK from the receiver. So in summary Acknowledgements are used to confirm the receipt of the message. Acknowledgements are implemented at two levels transport level and application level. In this post we will have a look at both the options.

Transport Level Acknowledgements: Sending systems open a connection to send messages to the receiving messages, mostly through the interface engine which act as broker for communications between different systems in a healthcare setup. If a message is acknowledged on the same connection which is used to send a message they are termed as transport level acknowledgements.

The connections can be transient or persistent in nature. Transient connections are those where the connections are closed after an acknowledgement is received. Each time a message is sent a new connection is made. Persistent connections are those where the connections are kept open and messages are sent over the same connection in a sequence, in sense sending a next message over the same connection after an acknowledgement is received for the previous sent message. Persistent connections are generally configurable where the connections can be closed after a certain period of inactivity. There are different factors which determine the choice of connection. The factors include message throughput, latency, sequencing, fail over, high availability and general infrastructure of the organisation.

Transport Level Acknowledgements also indicate that the ownership of the message is passed to the receiving system after it has received a acknowledgment. The transport level acknowledgement also informs the transport and reception error.

If a message is received and accepted by the receiver then it sends a ACK and performs one of the following

•Validates and persists the message successfully, generating the functional response message with a value of AA (Application Accept) in MSA-1-acknowledgment code field.

Or

•Send an error response, providing error information in functional segments to be included in the response message with a value of AE (Application Error) in MSA-1-acknowledgment code field.

Or

•Fail to process (reject) the message for reasons unrelated to its content or format (system down, internal error, etc.). For most such problems it is likely that the receiving system will be able to accept the same message at a later time. The sending system must decide on an application-specific basis whether the message should be automatically sent again. The response message contains a value of AR (Application Reject) in MSA-1-acknowledgment code.

Application Level Acknowledgement: A sending system may require an application level acknowledgment from the receiving system if confirmation of successful processing is required. This can take the form of an HL7v2 ACK message (e.g. to indicate a successful processing of order it received) or a business response.

Generally the transport acknowledgment only confirms the receipt of messages but does not convey any confirmation of processing of the message. The need for these interfaces needs to be decided by the business processes. They are transmitted in the same way as any other message

In HL7 terminology the above two types of ACK's are termed as follows

•Original Mode Acknowledgement - a "Receive" ACK and majority of the ACKs used in HL7 communications; indicates that a message has been received but not necessarily processed yet

•Enhanced Mode Acknowledgement - an "Application" ACK that is a resultant status return rather than a communication response (i.e. query results, order response, etc.)

Healthcare ESB Approach

This post defines an approach which can be used for development of Enterprise Service Bus to enable communication using both HL7V2.x and HL7V3.0. The approach is based on Service-Oriented Architecture (SOA) to better align the solution with the business. Enterprise Service Bus (ESB) has emerged as the best proven, fastest and simplest way to implement SOA and offers dramatic productivity and ROI improvements over traditional integration technologies. Figure below a schematic representation of proposed ESB involving applications communicating using both HL7V2.x and HL7V3.0.

ESB Model


SOA simplifies the complexity in integration by the provision of a common infrastructure for service communication, mediation, transformation, and integration. ESB serves as the backbone for an SOA implementation. The ESB will provide the following services

Transport Services: The transport services need to support multiple communication protocols to support both local and national communication. The relevant communication protocols for the current scenario that will be supported are TCP-IP/MLLP, HTTP(S) and JMS.

Message Type: The solution need to support multiple messaging models such as synchronous, asynchronous, publish, subscribe and store and forward. The message types supported with these messaging models are JMS with headers, XML, SOAP and ebXML.

Validation Services: The messages come in different formats varying from string delimited for HL7 v2.x, XML for V3.0 and proprietary formats for existing systems. The validation components will vary from using standard XSD’s to custom XSD’s.

Transformation Services: The transformation service is required to transform currently one version of HL7v2.X to other versions of HL7V2.x and some custom format. The functionality supported by transformation service is
Ø Transforms messages based on the target service
Ø Transforms messages based on XQuery or XSLT
Ø Supports transformations on both XML and string delimited messages

Routing Services: The routing services need toallow routing of messages to existing systems and national applications based on the message content or message headers. The routing services will be based on XQuery-based policies or callouts to external Web services. The routing policies apply to both point-to-point and one-to-many routing scenarios.

Service Management: The service management services need to help handle logging, monitoring and error handling variety of message errors. The logging and monitoring will support logging messages for both systems operations and business auditing purposes, search capabilities, and others. Both business services and ESB services are monitored, as are response times, message counts, and error counts. The error handling components allows configuring of systems to format and send error messages, and return messages for consumers of services who expect a synchronous response.

Common Wrapper: The differences in transport mechanisms used by HL7V2.x and HL7V3.0 will hinder the ESB. The development of a common wrapper with elements of MLLP wrapper and SOAP/ebXML wrapper is crucial for successful deployment of this model.

HL7V3 and ebXML - Part 3

I apologise for the delay in publishing the Part 3 of the ebXML and HL7V3. I see that a portion of hits to my blog are coming from the links provided by Marc de Graauw in Section 7 of his article Implementing “Web Services in Dutch Healthcare” at http://www.ringholm.de/docs/03030_en.htm. I thank him for considering my blog posts worth the mention.

What is ebXML MSH?

HL7 V3 message triggered from Sender are sent over their integration layer as HL7 Request to sender MSH (Message Service Handler). MSH is a piece of software used to send and receive ebXML messages. Figure below shows the functions of MSH.

The textual description of the services depicted above is given below

Ø MSH Service Interface – This is the abstract interface applications use to interact with MSH to send and receive messages.

Ø Header Processing – the creation of the ebXML Header elements for the messages sent from the applications. It also involves parsing of header elements and interactions with contract properties. [See below for Contract Properties]

Ø Security Services – this includes digital signature creation in the messages (which may be used in headers), verification, encryption, authentication and authorization.

Ø Message Packaging – this will perform the enveloping of an ebXML Message (ebXML header elements and payload) into its SOAP Messages with Attachments container

Ø Reliable Messaging Services – this service handles the delivery and acknowledgment of ebXML Messages. It also deals with persistence of messages, retry, error notification and acknowledgment of messages requiring reliable delivery.

Ø Transport Binding – This is the abstract interface between the MSH and the various protocol stacks.

Ø Error Handling – this handles the logging and reporting of errors encountered during MSH or Application processing of a message.

Contract Properties

To understand the exchange of messages between two MSH’s we need to understand the term “contract properties”

Each MSH processes the messages sent by the other MSH by the contracted interface properties. These properties describe Quality of Service (QoS) from reliability and security point of view. The MSH uses these properties to build the ebXML wrapper. The contract properties are defined during message definition process and agreed between two organizations or two system vendors who will exchange the messages. Contract properties are defined for each HL7 interaction. The contract properties given for each interaction are identified by a CPAId. The sender will use the CPAId that is relevant for that HL7 message interaction and agreed with the receiver.

The relevant contract properties are Service, Action, Persist Duration, RetryInterval, Retries, AckRequested, SyncReplyMode, Actor, EndPoint, IsAuthenticated etc.- See HL7V3 and ebXML – Part 1 for details about these properties.

ebXML Message Exchange :

Figure below shows the sequencing involved in ebXML message exchange

Let me explain the flow in the above sequence diagram

1. In a typical implementation the Sender builds the HL7 message with the HL7 Wrapper and passes it onto the sender MSH

2. The sender MSH looks at the message interaction id and looks up in the database for the contract properties for the message and builds the ebXML wrapper.

3. The ebXML message sent by sender MSH containing the HL7 message payload will get ebXML acknowledgement synchronously on the same connection over HTTP 202. The ebXML Acknowledgements are sent without a payload.

4. If the ebXML acknowledgement from Receiver MSH is not received within a time interval Sender MSH resends the message. The number of retries and retry time interval are dependant upon the contract properties attached with that message.

5. If the number of retries expires depending upon the message business functionality Sender MSH will report the error back to application which sent the message or enter into a HL7 slow retry method.

6. In case of ebXML errors Receiver MSH sends a message with the same end-point binding associated with ebXML acknowledgement service except that a Message Error will be sent.

7. The business responses or application acknowledgements from Receiver MSH in response to the message sent are received and processed by the Sender MSH exactly in the same fashion as Receiver MSH does on receiving a request from Sender MSH.

The above description is only for direct reliable message exchange between two MSH's ; we can have intermediary exchange with two MSH's communicating to each other using anothe MSH or we can also have direct unreliable message exchange. I have not discussed them here not i do intend to discuss them here.

HL7V2.x and Low Layer Protocols

Minimal LLP (MLLP) and the Hybrid LLP (HLLP) are the two widely used lower layer protocols (LLP) for HL7 versions 2.x transmission. They are efficient and extremely simple to implement and use simple socket based communication. MLLP and HLLP does not really qualify as a "protocol" as they make use of TCP's reliability. MLLP and HLLP are simply a means of framing individual HL7 messages which is needed at the 7th level.

There are two types of LLP connectivity

Ø Persistent - In this type of connectivity socket is cached based on the endpoint and only one socket per endpoint is created and reused for the next set of messages.

Ø Temporary - In this type of connectivity a new socket is created for each message. When a message is sent the sender waits for the ACK and once it is received socket is closed.

The processing rules for both MLLP and HLLP are more of less the same; however, processing rules for HLLP include additional logic to signal transmission errors.

MLLP Wrapper

The MLLP wire format looks like <SB>dddd<EB><CR>

Where <SB> is Start Block, 1 Byte, ASCII <VT>, HEX <OxOB> and should not be confused with ASCII characters SOH or STX.

dddd is the HL7 variable length HL7 message. The data can contain any displayable ASCII characters and the carriage return character, . <CR>

<EB> is End Block, 1 byte, ASCII<FS> , HEX <Ox1C> and should not be confused with ASCII characters ETX or EOT.

<CR>is Carriage Return, 1 byte, ASCII , HEX <OxOD>

HLLP Wrapper

The HLLP wire format looks like <SB>tvv<CR>ddddCcccc<EB><CR>

Where <SB> is Start Block, 1 Byte, ASCII<VT> , HEX <OxOB>and should not be confused with ASCII characters SOH or STX.

t is Block Type, 1 Byte. ‘D’ is data block. This is used for HL7application message and HL7 ACK response message.‘N’ is NAK block and is used only as NAK to signal transmission errors

vv is Protocol Id, 2 Bytes. The characters ‘2’’1’ for this version

<CR>is Carriage Return, 1 byte, ASCII<CR> , HEX <OxOD>

dddd is is the HL7 variable length HL7 message. The data can contain any displayable ASCII characters and the carriage return character, <CR>.

In a NAK block, this field contains a 1-byte reason code as follows:
‘C’ is character count wrong in previous data block received.
‘X’ is checksum wrong in previous data block received.
‘B’ is data too long for input buffer in previous block received.
‘G’ is error not covered elsewhere.

Ccccc is Block Size, 5 bytes and is the character count of all characters so far in the data block up to and including the last data character. For this version of the protocol this is 5 + the size of the dddd field. An encoded HL7 message ends with a <CR>character. This character is considered part of the data.

Xxx is Checksum, 3 bytes an X-OR checksum of all character in the block up to and including the last data character. The checksum is expressed as a decimal number in three ASCII digits. If the value is 999, the checksum should not be computed. Processing will proceed as if the checksum were correct. This feature is used for applications where the messages will be translated from one character set to another during transmission.

<EB>is End Block, 1 byte, ASCII<FS> , HEX <Ox1C> and should not be confused with ASCII characters ETX or EOT.

<CR>is Carriage Return, 1 byte, ASCII , HEX <OxOD>

Null Values in HL7V2.x

In HL7V2.x the null value is indicated by ¦""¦. When a system receives this it interprets that the particular attributes value has been changed to null as the sending system has deleted the value of that particular data element in its database. It also indicates that the data element is available in the sending system’s database but currently not valued. The receiving system on receiving it should change the current value to null for that data element. However the absence of a field (¦¦) from sending system indicates that the value of the absent element may not have changed since the last event and the receiving system should retain the current value. The absence of a field (¦¦) may also indicate that the particular data element is not available in the sending system’s database.

A few tips on interpretation of "null" value and "not available" in HL7V2.x messages for application programmers

1.If the HL7 NULL value is present in message received and if the application processing allows a field to be changed to null for this source, the Interface needs to null existing application data elements.

2. If an optional non-repeating field or entire optional segment is absent in a received message, the Interface must not null the existing application values.

3. The application Interface should not support partial updates of repeating data. If some fields in a set of repeating fields are absent or null, the Application Interface may inappropriately overlay valid data or retain unwanted values. The Application Interface must not “error” the message.

4. The Application Interface must not support partial updates of repeating prioritized segments. If some segments in a set of repeating ordered segments are absent, the Application Interface may inappropriately overlay valid data or retain unwanted values. The Application Interface must not “error” the message.

5. When a message is sent the Application Interface must value all available changed and unchanged data elements in a segment

6.The Application Interface must send all instances of a repeating field.

7. The Application Interface must send all instances of repeating prioritized segments. For segments that repeat but can be uniquely identified and updated as an atomic unit, the Application Interface may send only the segment that has changed.

8.The Application Interface must send a null value for attributes that are present in the application database but have a null value. The option to send the HL7 null value need to be configurable by feed and not by field. The Application Interface must interpret zeros in a date field as null and zeros in an Application coded value field as null; however, the Application Interface must interpret zeros in a numeric field as a valid value.

Weakness of HL7V2.x

Inter-Intra Enterprise - HL7 V2.x limitations came to the fore with the advent of Electronic Health Record (EHR) which involves exchange of data across organizations. The need for inter-enterprise data exchange exposed the ambiguous data semantics of HL7V2.x which is due to the fact that version 2 messages are based on no explicit model .For example relationship of OBX to OBR and ORC to PID is implied but not specified. Fields within a message originate from different implicit data models and lead to inconsistent interpretation of these fields.

Semantic Framework - The presence of semantics framework is crucial in understanding the definition of each element of data in the message and the relationship with other data elements. It is also crucial for representing coded elements and relationships within the terminology. So the absence of a semantics framework in HL7V 2.x messages makes it mandatory that the applications involved in the exchange of data needs to be programmed to interpret the different values that come in a field from other applications. This need for interpretation of messages by applications using programming increased the costs and effort for deployment of HL7V2.x messages.

Backward Compatibility - The mandatory requirement of maintaining backward compatibility between different versions of HL72.x is an overhead and constrains HL7V2.x from adopting new terminology and communication standards. This constraint led to version HL7V2.x being termed more of a data exchange standard rather than interoperability standard.

Data Relationship - There is a vague definition of relationship between message types, event types, and the structure of a message in HL7V2.x. There are no clearly defined rules describing the association between events and messages. For example in version2.3 a single ORM message is associated with different events such as new order, modify order and cancel order. In some scenarios the event types describes the message structure and the real time events associated with the messages and in other scenarios it describes the location of the target system where the data in the message has to be transmitted.

Methodology - There is no explicit methodology defined for building of HL7 V2.x messages. There is no detailed documentation associated with specifications to give guidance to developers and implementers on constructing HL7V2.x messages. Trigger events and data fields are described in formal language. The same message definitions are used for different trigger events. The different chapters in the documented specifications are not consistent in usage of trigger events and status codes. The specification concentrates solely on the behavior of sending system and does not define the receiving systems behavior nor does it provide guidance when a specific receiving system is expected to honor a trigger event or accept a message. HL7V2.x methodology is based on structured programming language but does not have formal operations and object oriented concepts such as generalization and specialization hierarchies.

Optionality - There is a substantial amount of optionality built in HL7VV2.x messages making it difficult for specifying precise contract terms for HL7 interfaces. Optionality also led to vendors making ambiguous HL7 conformance statements as it is difficult to define the exact semantics of a specific message. The use of optionality increased the costs of development of interfaces for applications which came with out-of-box HL7 interfaces. This led to HL7V2.x being termed as not a plug-and-play standard which usually is required for messaging standards in any industry for e.g. SWIFT standards for banking.

Security – Security has been always considered out-of-scope for HL7V2.x messages. There is no explicit support for security functions such as encryption, restricted access to data and digital signatures.

Strengths of HL7V2.x

Strengths of HL7V2.x

Mature Standard – HL7V2.x emerged as a mature stable standard in healthcare informatics after the specifications went through series of review iterations and modifications to cater to the needs of market. The HL7V2.x specifications are currently available and ready for use and easily implementable. A large number of existing applications are HL7V2.x conformant.

International Standard – HL7 has international affiliates in around 28 countries covering all major countries. It has emerged as the dominant clinical information standard in these markets. Majority of the HL7V2.x specifications including HL7V2.3/2.4 have been classified as ANSI accredited standards. HL7V2.4 is now being proposed as ISO standard. Apart from this some countries such as Germany have legislations that stipulate use of HL7V2.x.

Backward Compatibility - The biggest advantage of HL7V2.x is the ability of different versions of HL7V2.x to interoperate with one another. The rules for compatibility between different versions (e.g. V2.3.1, V2.4 and V2.5) have been documented in the specifications. These rules describe the transmission and receipt of messages and converting their contents to data values with full backward compatibility between all HL7V2.x versions.

Optionality - The use of optionality in HL7V2.x messages is helpful in gaining consensus and documenting compact specification. If a data field is declared optional within a segment then the segment can be re-used in different messages without defining a new segment which requires similar data fields. However there is a wide misuse of this optimality which will be discussed in next section.

Message Size: The chief virtue of HL7V2.x message specification is that its syntax is quite compact and hence the size of the message is minimal. This brings a huge benefit to the economy of bandwidth

HL7 Operation Forms

HL7 message exchange behaviour is governed by two forms of operation
· State Exchange Form(SEF)
· Remote Invocation Form(RIF)

State Exchange Form (SEF) is used to synchronise business processes running in separate systems usually across organisations. That is a business process engine in one organisation aligns the state of its process with a business process engine in another. SEF is usually performed through HL7 messages using reliable asynchronous ebXML pattern. Examples where SEF is used is in case of updates to patient demographics or creation of a new patient in a local system. The changes are initially done in the local application and then the external systems are notified of the changes through update or create messages. The external systems then use the data in these messages and update the data to keep in sync with the sending system.

Remote Invocation Form (RIF) is derived from standard client-server methods. The model is inherently synchronous from the perspective of the human actor in that the actor is “blocked” waiting for a response. RIF is usually performed through HL7 messages using synchronous Web service pattern or unreliable asynchronous ebXML pattern. Examples where RIF is used is in case of queries and retrievals of data from other systems. The sender system sends a query to the receiving system which maintains the MPI for the organisation and uses that data for further processing.

HL7/ebXML Slow Retry

ebXML Retries


According to ebXML Message Service Specification Version 2.0 a MSH (Message Service Handler) will perform multiple retries to send a message if it(sender) does not receive an Acknowledgement from the receiving MSH. The number of retries is one of parameters used by the sending MSH to confirm that a message is sent reliably.

According to ebMS2.0

Ø The Retries parameter is an integer value specifying the maximum number of times a Sending MSH SHOULD attempt to redeliver an unacknowledged message using the same Communications protocol

Ø If the Sending MSH does not receive an Acknowledgment Message after the maximum number of retries, the Sending MSH shall notify the application and/or system administrator function of the failure to receive an Acknowledgment Message.

From the second bullet point it is clear about what ebMS2.0 suggests us to do.

According to the classic Enterprise Integration Patterns "messaging" ensures that message will be guaranteely delivered but does not guarantee when it will be delivered. If the infrastructure supporting the conversation between sender and receiver is down for considerable time the sender will ensure that the receiver gets the message when the infrastructure is back. However when the message is delivered the context of the message may not be valid anymore. Generally systems implement message expiration that is if they receive a message which is quite old they discard the message and the “oldness” of the message usually is implementation specific. In some cases the messaging middleware implements the message expiration policy where it specifies how long a particular message type will live or when it will expire. The expired messages are written into dead letter queues for service management activities.

But ebMS2.0 does not specifically talk about what to do after the number of reties expire other than letting the layers above the messaging layer know of the failure to deliver the message. It also does not talk of the slow retry mode (or is it called long retry mode?) or about message expiration at all except for the number of retries as per the contract property.

In one of the large HL7V3.0 implementation where ebXML is implemented for asynchronous messaging it was recommended that systems use HL7 retry mode when sender MSH retries expire without an ACK being received from the receiver. In this particular implementation the system provider suggested that all systems which communicate with a particular sender should implement the “Slow retry” as exponential retry behavior that is, after each ebXML request sequence has failed, the Sender must retry with an increasing time interval. This might run into a problem for outages of longer duration as the persistent duration of the message might expire if at all the message has been received by the receiver but the acknowledgment has not reached the sender from the receiver.

According to ebMS2.0 persistent duration is a parameter which is defined as the minimum length of time data expressed as "duration" from a reliably sent message is kept in persistent storage by a Receiving MHS node. If the persistent duration has passed since the message was first sent, the Sending MSH SHOULD NOT resend the message with the same ebXML MessageId though the HL7 Message Id should be the same.

If response is not returned even after ebXML retries and “slow retry” there is no other way other than handling the problem manually. In case of Multi-Hop using a intermediary slow retry is not suggested at all it has to be handled manually as Multi-Hop do not conform to eith SEF or RIF(See my post on HL7 Forms of Operation)

Healthcare ESB Requirements

This is a summary of requirements for a ESB in a healthcare setting from my point of view.

Design and Development

1. The solution needs to support the proposed SOA/ESB reference architecture where the ESB is single point of integration for all the organizations requirements for communicating to internal systems and external systems. The tool sets used for the proposed solution needs to be interoperable from development perspective. For example the BPM tool needs to be integrated with development tool set.

2.The solution needs to be able cater and extend to alternative frameworks to SOA such as Model Driven Architecture and Event Driven Architecture.


3.The solution needs to adhere to a typical development lifecycle. The product suite needs to provide tools for design, development, testing, deployment and support.


4. The solution needs to provide tool sets to support XML, XSD authoring, XSLT (XML Transformation) and XPath.


5. The product suite used for the ESB needs to quicken development using off-the-shelf frameworks and support for health care standards such as HL7 , ASTM , DICOM etc.



Solution Framework

1.The ESB solution needs to support variants of HL7V2.x to support communication of local systems within an organization. The ESB needs to support backward compatibility of HL7V2.x messages by selective validation of message segments as per the version.


2.The HL7V2.x message types that need to be supported by the ESB primarily are ADT, Inbound Orders, Outbound Orders, Inbound Results, Outbound Results and Scheduling.


3.The HL7V2.x messages will contain user defined Z-Segments apart from standard segments originating from clinical applications and other existing systems. These messages need to be validated by the ESB against the standard specifications and rejected with a response back to the target system for possible resubmission.

4.The ESB needs ensure that messages from each clinical application are routed correctly to the target system.

5.The ESB needs to support persistent and transient connections from and to the organizations applications.

6.The ESB needs to support message sequencing and deliver the HL7V2.x messages to the clinical applications in the order they arrive at the ESB.

7.The ESB needs to provide duplicate elimination without compromising the ability to process messages faster.

8.The ESB needs to ensure message accuracy. Accurate means that the content and structure of a Message is maintained from the moment of receipt or generation of the Message by the ESB to the moment of Transfer, or completion of all required processing, of the Message by the system till it is delivered to target system.


9.The ESB needs to support Remote Invocation Form (RIF) that is derived from standard client-server methods. The model is inherently synchronous from the perspective of the human actor in that the actor is “blocked” waiting for a response. For RIF the ESB needs to keep the connection open till the response is back and do not allow a message to be fired with the same message id by the user. Allow the user to fire the same message with different message if a SOAP HTTP 2xx indicating failure for the first message comes back

10.The ESB needs to support State Exchange Form (SEF) that is used to synchronize business processes. In SEF application persists the data and sends the message to target system. The ESB needs to close of the connection. When the target system responds back it may be a success or failure. The success needs to conveyed back to application but not the failure. The failure needs to be logged by ESB for it to be investigated


11.The ESB needs to support ebXML mode for asynchronous messaging to applications. The ESB needs to build HL7 wrappers and validate payload from applications. The ESB needs to include HL7 wrapper and payload within a SOAP envelope, and transport the full message over HTTPS. The information behavior for MHS needs to be in sync with Oasis ebMS V2.0

12.The ESB needs to support both Single Mode and Intermediary mode for ebXML asynchronous messages.


13.The ESB needs to support SOAP-WS for synchronous messages to applications. The Web Services Mode of ESB is delivered by considering the target systems integration layer as a standard Web Service provider. The service provider MAY produce a WSDL definition for each web service. However, the WSDL is not warranted to generate web service stubs. This is due to the diversity of tools and the inability to guarantee that the WSDL will operate correctly in all environments. Implementers may use the WSDL to build product-specific WSDL, or implement the service interfaces in some other manner.


14.The ESB needs to support integration of legacy systems using different communication protocols like TCP-IP , MQ , FTP , HTTP , Web Services

15.The ESB needs to support proprietary queuing methods like variants of JMS and other queuing mechanisms.

16.The ESB needs to support sending of alerts to users using variety of communication methods – SMS , e-mail(SMTP) and Paging


17.The ESB should provide standard adapters of the product and its licensing policies associated with them. The adapters should cover communication protocols , database connectivity , transformation , message transport and message

18.The ESB needs to support LDAP and the ability to query LDAP for retrieving contract properties , CPA and possible reference data and route the responses to appropriate system.

19.The ESB needs to support message patterns – asynchronous and synchronous messaging –publish and subscribe – store and forward- push and pull mechanism.


20.The ESB should support internal interfaces which need not be HL7 v3 compliant interfaces and the HL7 v3 compliant interfaces and communication with the applications so that communications can take place between IT systems where one IT system is within the organizations boundary of responsibility and the other IT system is outside the organizations boundary of responsibility.

21.The ESB needs to support multiple versions of HL7V3 message interactions. The ESB needs to support the concept of sending a single HL7V3 message to multiple target systems.

Deployment

1.The ESB needs to be deployable in distributed and federated fashion with ability to monitor and support from a uniform platform.

2.The ESB need to have minimum downtime requirement for configuration changes and upgrades.

High Availability and Scalability


1.The ESB need to support large data volumes including large message sizes and high through put. Please mention the ability the solutions ability to support multi-threading without consuming infrastructure resources to support increase in volumes.


2.The ESB need to support different High Availability options using load balancing, clustering and failover methods without any loss of messages. The High Availability expected for the ESB is 99.9

Security

1.The proposed solution framework needs to be ensure that all messages sent over the internet need to be secure. The solution needs to ensure that there is no user based access to the ESB from external data sources other than via the defined messaging interfaces.

2.The ESB needs to provide Security Framework and Infrastructure with ability to encrypt and decrypt messages and support for creation, installation and deployment of Certificates.



Service Management and Support


1.The ESB needs to be provided a framework to log message attributes such as the message creation date/time, message identifier, referenced message identifier (for response messages), the message interaction identifier, message status (success or failure) and the unique row identifier into the audit queue where the audit event (HL7 message, SOAP message or ebXML Acknowledgement) is held.

2.ESB needs to log the error codes and the associated text returned in the message responses of failed and unsuccessful messages. A browser based Message Log Viewer needs to be provided and allow a user to search audit log and select to view a specific message from the audit queues.

3.The Message viewer should allow only the message headers to be viewed; the message body should not be allowed to be viewed.

4.The ESB framework need to be support error handling and log communication and mapping errors and should be viewable from the Message Viewer. The error logging framework needs to log alias translation, errant data, and functional errors.


5.The service management framework of ESB needs to be integrated with standard Service Management tools of IBM and CA.



Testing

1.The ESB testing framework needs to acts as test Harness for testing both HL7V2.x and HL7V3.0 messages.

2.The test Harness need to provide a UI (User Interface) with ability for application testers to setup test data needs to be incorporated

3.The test harness needs to be a virtual application providing the responses in sync with the expectation of the ESB.

4.The test harness needs to be readily configured to test all business cases of the organizations applications. The rules configuration also needs to be user interface based instead of using technologies like XPATH

Decoupling Mode Handling

1. The ESB needs to handle delivery of messages when target system is not available manifested by a failed http connection.

2. The ESB needs to handle failed delivery of messages manifested by in the ebXML message mode by non-receipt of the ebXML Acknowledgement following the required number of retries.

3. The ESB needs to operate in slow retry mode after the expiry of retries in ebXML mode

4.The ESB needs to covey to the application of non availability of applications for synchronous messages manifested by non-receipt of the HL7 response.

5. The ESB needs to handle failure to deliver HL7V2.x messages manifested by failed TCP-IP connection and target system not available.





Supplementary Requirements

1. The ESB needs to provide the ability to longitudinally construct patient’s journey with data retrieved from different clinical systems and display in a consistent and fashioned approach to the end user.

2. The ESB needs to support the ability to support presentation layer integration using CCOW and other relevant standards.

Message Sequencing in HL7V2.x

Maintaining message sequencing when clinical systems are integrated with in an enterprise using middleware approach and HL7V2.x message specifications is crucial from two perspectives

• Delivering messages in the order is crucial for HL7 messaging; for example an A03-Discharge message cannot arrive before an A04-register a patient or A01- Admit notification. In case of orders a Modify Order cannot reach before a Create New Order is sent
• If a sender needs to send an extremely large message to a receiver, typically containing multiple OBX segments it is impractical to send all the segments into a single message as it will not fit into a single message. The breaking the message into parts and sending each of the parts as a separate message requires that each message needs to indicate its position in the sequence and indicate the total number of messages to expect.

The obvious solution to maintain the messages in sequence in the order they are received and to keep them in sequence as they travel through the middleware-Integration Engine. The solution may be as simple as sending all HL7 ADT messages from the HIS/PAS system to departmental systems in the hospital in the order that they were generated. This can be done by allowing a single-threaded route from the originating application usually the HIS/PAS to the middleware-integration engine. This usually means implementation of a behavior where messages are sent to a single point (Fixed IP address and Port number) and a receipt of acknowledgement message for the previously sent message before the next message is sent.

However for large organizations with huge volumes of messages it is not feasable to maintain a single thread and implementation of multi-threading might disrupt the delivery of messages in the order which they arrive.


One way to solve the problem associated with message sequencing for multi-threaded solutions is to keep messages in sequence that contain information related to the same entity which can be the patient identifier and allow the middleware to route all the messages related to a particular patient or a rane of patinets based on the patient identifier range over the same thread.

Approach – A – Single Threaded Solution

Messages must be delivered by the sending system in sequence using a single communication channel with the integration engine. Messages are received from HIS/PAS through TCP/IP Socket Listener and are allocated a sequence number. The sequence number, and message control id (MSH-10) are persisted either onto the disk or to the database associated with the integration engine. Each of the message that is sent are checked against the stored sequence number and message control id to verify if messages are sent in sequence.

Approach – B – Multi Threaded Solution

When a message is received by the middleware it is allocated a sequence number and the number along with the patient id taken from message are persisted to the disk or database. In case of multi-threaded solution the messages can be processed in parallel by any of the thread which subscribes to the publisher of the message. The thread which picked up the message for processing checks to see if a message has been is delivered through that thread for the patient in the message by looking at the patient id. If it is established messages for that patient in fact have been sent through that thread then a check is made to see if the sequence number of the current message is greater or lower than previously sent stored message. On confirmation of the value of sequence number value the message is delivered to the destination system. The delivery status of the message can be stored in the system so that in case of non-delivery suitable rehydration mechanism can be established before delivering the next message with the same patient id.

20 Minute HL7V2.x Primer

HL7 V2 Philosophy

The philosophy of HL7V2.x is based on the assumption that a real event that occurs in a healthcare setting creates data that needs to be exchanged between different systems of that setting. This is essentially to eliminate duplication of data collection from the patients and to automate administrative process saving time and money.

The real world events e.g. patient admitted or Lab orders raised are represented by trigger events and messages are specified for each trigger event. The structure of an HL7v2.x message is shown in Figure 1 below

Figure 1: Version 2 Message Structure

Segments - Version 2.X messages are designed around message segments indicated by a three letter segment id e.g. PID – Patient Identification; ORC- Common Order etc. Each message is composed of a group of segments in a defined sequence. Segments of message many be mandatory or optional and may repeat .A segment is a delimited line of data that contains data relevant to one specific use in the message. For example, patient identification information is in PID segment while patient allergies are defined in AL1 segment. Groups can be thought of as simply a collection of segments or other groups.

The HL7V2.x standard specification defines the standards segments. However the messages can also contain segments that are not part of the standard. These segments are locally-defined segments, called “Z-Segments” as their Segment ID code begins with a “Z”. These are allowed to add flexibility to the standard and usually appear at the end of the relevant segment group.

Each segment is a logical grouping of data fields. then composed of data fields. Each data field can have one or more components and each component may have sub-components.

HL7 V2.x History

HL7 1.0 originated in 1987 as an open standard for vendors for interfacing different clinical systems within an organization. It was defined in a period of six months with initial set of Orders and ADT messages. They were not widely implemented but laid a foundation for defining standard healthcare interfaces. HL7 v2.0 which was demonstrated at 1989 HIMSS convention introduced the concept of triggers, added additional detail to the Message header, and expanded the set of messages to include billing. HL7V2.0 was also not widely implemented. Figure 2 below shows a timeline of HL7 Version 2 releases.

Figure 2: Version 2 Timeline

HL7 Version 2.1 - HL7 Version 2.1 is the first widely used standard after its publication in March1990.HL7 2.1 is still in use today by some clinical systems.

HL7 Version 2.2 - HL7 Version 2.2 is primarily centered around cleaning up and clarifying version 2.1 specifications The notable changes to version 2.2 among others is that Segments were added to existing events for e.g. Merge Segment was added to the Transfer events (A06 & A07); Next of Kin Segment was added to the Patient Query (A19) event. Some additional fields were added to segments for e.g. additional fields to PID segment to handle newborn baby information and Next of Kin was made more generic to handle any person associated with the patient. New messages to handle Pharmacy, Diet and supply orders were added. Apart from adding new data types the HL7 acknowledgment paradigm has been extended to distinguish both accept and application acknowledgments, as well the conditions under which each is required.

HL7 Version 2.3 - Version 2.3 offers new data types, especially the 'x'-tended versions of PN, CN, etc. Enhanced query functionality and clear definitions of tables for e.g. differentiating ID/IS data types. In Financial Management Additional messages were added and message constructs were extended to allow greater specificity in the intent of the message, and to report additional information.

HL7 Version 2.3.1 - HL7 V.2.3.1 includes an updated TQ (timing/quantity) datatype to manage order occurrences, updates to the OBR segments and ORU message to facilitate public health surveillance reporting, updates to tables, segments and data types to accommodate international paradigms for reporting names and pharmacy orders, and the addition of a new field to the ORC segment to satisfy the HCFA Medical Necessity requirements for outpatient services, and an update to the FT segment to satisfy federal requirements for Level 2 Modifiers.

HL7 Version 2.4 – Version 2.4 is approved as an ANSI standard in October 2000. HL7 v.24 introduces Conformance Query profiles, and adds messages for laboratory automation, application management and personnel management. Additionally, a new event, specific to OPPS and APC requirements was added. This event, Transmit Ambulatory Payment, includes two new segments, the Grouping/Reimbursement Visit Segment and the Grouping Reimbursement Procedure Segment.

HL7 V2.x Message Construction

Message Encoding Rules: Version 2.x messages have some defined special characters that delineate data fields which make up the message. These special characters are the segment terminator, the field separator, the component separator, the sub-component separator, and the repetition separator. Table 1 below shows the definition of these separators


Table 1: Version 2 Separators

The interface that implements version 2.x messages will use escape sequences for e.g. \F\- Field Separator to signify that reserved characters (delimiter or separator characters) is present in the value

Message Construction Rules: A Version 2.x message consists of segments. Message segments are constructed in the order defined below

1. The first three characters in the message segment that will be inserted into the message is the segment ID code, e.g. - PID – Patient Identification Details.

2. Each segments consists of different fields and each of those data fields that make up a segments are inserted into the segment in sequence:

2.1 A field separator ¦XYZ¦ is placed at the beginning and the end of the field. If there is no value present in the field then no other characters are required and a ¦¦ is used.

2.2 If the value is present but equivalent to null, two consecutive quotation marks are placed in the field ¦""¦.

2.3 If a field is defined to have components (combination of meaningful data fields), the following rules apply:

• Components are separated by the component separator.


• Components that are present but null are represented by two consecutive quotation marks


• Components with no value require a component delimiter but do not require characters in the component. For example: ¦ABC^^DEF¦


• Components at the end of a data field with no value do not have to be represented by a component delimiter. For example: ¦ABC^DEF^^¦ = ¦ABC^DEF¦


• When a component is itself a data type that contains components, its delimiters are demoted by one. For example, the component delimiters for the composite field ¦ABC^DEF¦ are demoted by one to ¦JKL^ABC&DEF¦

2.4 If component has sub-components, the following rules apply:

• Sub-components are separated by the sub-component separator.


• Sub-components that are present but null are represented by two consecutive quotation marks.


• Sub-components that are not present require place holder separator but no characters in the sub-component.


• Sub-components at the end of a data field with no value do not have to be represented by a sub-component delimiter.

2.5 If the field definition permits repetition, the repetition separator is used only if more than one occurrence is transmitted. The repetition separator is placed between occurrences.

2.6 End each segment with an ASCII Carriage Return character - ASCII(13), HEX(0D).

3. Steps 1 and 2 are repeated until all segments have been generated.

4. The receiving system will ignore segments, fields, components, and extra repetitions that are present but not expected. The receiving system will treat segments that are expected but not present as consisting entirely of fields that are “not present”, and it will treat fields and components that are expected but not included in a segment as “not present”.

Data Types: Data types define the structure of the fields. Data type specification is an important tool for simplifying the complexity of the HL7 standard, and is critical for understanding the data contents of an HL7 field.

Version 2 supports the following data types

• Primitive – consisting of one component e.g. ST(String)


• Simple – multiple components, no ‘type’ code e.g. CE (Coded Element)


• Complex – multiple components with a ‘type’ code e.g. XAD(Extended Address)

The application of data types to the fields can be gauged by the following examples.

The format of CE as per version 2 specification is

CE :< identifier (ST)> ^ <text (ST)> ^ <name of coding system (IS)> ^ <alternate identifier (ST)> ^ <alternate text (ST)> ^ <name of alternate coding system (IS)>

e.g. 11289-6 ^ Body Temperature ^ LN

11289-6 is the identifier; Body Temperature is the text and LN (LONIC) is the name of the coding system.

The format of XAD as per version 2 specification is

XAD : <street address (ST)> ^ <other designation (ST)> ^ <city (ST)> ^ <state or province (ST)> ^ <zip or postal code(ST)> ^ <country (ID)> ^ < address type (ID)> ^ <other geographic designation (ST)>^ <county/parish code
(IS)> ^ <census tract (IS)>

e.g.: ¦23 Sussex Place ^Flat 3 ^ Slough ^ Berkshire^SL11NH^UK^P^^BERK^¦

23 Sussex Place corresponds to street address ; Flat 3 for other designation; Slough for city; Berkshire for state;SL11NH for postcode; UK for country and P which stands for permanent.

HL7V2.x Message Anatomy

Imagine the following scenario

• Patient Andy Smith Carol was admitted on July 22, 2006 at 11:23 a.m. by Doctor John Carol (#C145678) for an orthopedic procedure (ORT).



• He has been assigned to room 202, bed 10 on nursing unit 1000.



• The Patient Lives at 23, Sussex Place, Slough, Berkshire, SL11NH and was born on December 23rd 1961.



• The hospital the Mary Green Maternity – MGM has PAS System - ADT1 and a laboratory system PATHLAB.

The admission of the patient corresponds to a trigger for Admit patients and an event A01 is intended for admitted patients. This will be sent from PAS system to Lab system in real time as soon as the admission takes place. According to HL7 V2.3.1 message specifications a portion of message structure of A01 shown in Table 2

Table 2: A01 Message Structure

Download the complete A01 HL7 V2.3 message specifications from HL7 website (http://www.hl7.org/)

The most important fields in the message segment (MSH) header are shown below in Table 3.

Table 3: Relevant MSH Fields

The message segment MSH shown below sent in the message based on the scenario above shows what has been sent in the following scenario with the data items from the PAS database populating these fields.

The other important message segment PID in A01 whose important fields are shown in Table 4. The complete list of fields is available from v2.3.1 Message pack on HL7 Website.

Table4: Relevant PID fields

The message segment PID shown below sent in the message based on the scenario above shows what has been sent in the following scenario with the data items from the PAS database populating these fields.

Messaging Communication: The most commonly used mechanism for sending HL7 Version 2.x messages is Lower Layer Transport protocol (LLP). The messages are sent over TCP/IP over the network.

The protocol is very simple to implement using the implementation setting sockets. The protocol requires that that each message should be preceded with the character 0x0B (11) and followed with the characters 0x1C (28) and 0x0D (13). This is required for communications code to be able to recognize the start and the end of each message

Finally each segment is terminated by a 0x0D (13) character. This is mandated by the standard, but often HL7 log data can be received via ftp or email where the segment separators have been transformed into 0x0A characters, etc

Current Status of HL7V2

Some countries such as Germany have legislation that stipulates the use of V2.X, and V2.4 which is a ANSI standard from 2004 is now being proposed as an ISO standard, making it a truly international standard though it have been developed for American market.

The Version 2.x standards are widely used in different countries in the world, in particular in acute healthcare settings and in some countries even in primary care. The HL7 versions 2.1 to 2.5 which have been published are in wide use and the work is underway on V2.6, which is expected to be published late 2005/early 2006.

Version 2.5 – HL7 Version 2.5 is the last published standard in the HL7 Version 2.x series. Version 2.5 contains new messages and updates to HL7 Version 2.4. Version 2.5 is supposed to be broader in scope that Canadian Health Information Technology Trade Association (CHITTA) have issued a position paper to Canada Health Infoway urging the agency to reconsider its support of Health Level 7 (HL7) Version 3 in view of the supposed unavailability of Version 3 normalised specifications (Ref: Section xxx) and asked it to endorse HL7V2.5 which provides greater interoperability. HL7 Version 2.5 introduced a number of new events, segments and messages and expanded the Control section. Version 2.5 is more consistent and supports more functionality than any of the previous versions. The significant modifications to version 2.5 are

• Better and clearer documentation of the data types



• A definition of a message profile methodology



• Better support for Radiology/Imaging by means of a new segment and a new order message



• Support for orders related to blood products



• New update message for diagnosis/procedures



• New specification of claims and reimbursement messages

Version 2.6 - HL7 Version 2.6 completed the first ballot cycle in September 2004 and is nearing completion and will be released in 2006. V2.6 will include enhancements made to allow the communication of Electronic Health Record (EHR) information which is sighted as one of the biggest deficiency of version2.x. Version 2.6 is an upgrade to HL7 Version 2.5 and it includes new segments, fields, components and subcomponents necessary to apply either a documented regulatory requirement or a harmonization requirement with HL7 Version 2 material created by other committees. The main changes to version 2.6 from version 2.5 are

• Addition of general new segment -UAC "User Authentication Credential"



• Better management of access to sensitive patient information by adding Access Restrictions (ARV) segment.

• New message type to support the US National Animal Health Laboratory Network (NAHLN)



• Deprecation of data types such as CNN,LA1, LA2 and NDL data types



• Addition of components to the XAD and XTM data types.



• "TS" Timestamp data type is being replaced by the DTM "Date/Time" data type.



• CE "Coded Element" data type is being replaced by either the CNE "Coded with No Exceptions" or the CWE "Coded with Exceptions" data types

• Code tables defined by external standards organizations will not be considered as HL7 tables but an HL7 number will be assigned.



• Many new fields have been added to the segments in the Financial Management



• “Observation Reporting” chapter has added support for referral and shared care



• Personnel Management chapter contains new attributes to the STF and ROL segments.



• New chapter Materials Management with messages for communicating various events related to the appointment scheduling for services and resources

XML encoding :The German HL7 group defined a comprehensive database of the HL7 standard to allow consistency checks of items and to support the application of the standard by the user when they realized that the different chapters in the published standard have been developed by different groups and there are no distinct rules or guidelines for the development of various parts of the standard.

The database is a Microsoft Access database and contains the official definitions for events, messages, segments, fields, data types, components, tables and values. An XML representation of version 2.x standard is algorithmically derived directly from this database. The algorithm consists of SQL queries to extract tables which are then exported to ASCII delimited files. Perl scripts are applied to these ASCII files to generate XML DTD’s.

Two sets of DTD’s have been provided;
A single DTD (hl7_v231.dtd) that contains all HL7V2.3.1 definitions. This file is broken up into four separate DTD definitions – Message.dtd; segments.dtd; fields.dtd datatypes.dtd.

One DTD for each message structure. Each imports the same datatype DTD referenced by hl7_v231.dtd, but is otherwise self contained with all message, segment and field declarations needed for the message structure.

The XML representation represents HL7 message structures as XML elements. Message structures contain segments, also represented as XML elements. Segments contain fields, again representedas XML elements. A field's data type is stored as a fixed attribute in the field's attribute list, while a field'scontent model contains the data type components. Other fixed attributes are used to expand abbreviations and indicate HL7 Table value restrictions


A simple version 2.x representation is shown below



The representation of the above message using XML encoding rules is shown below.

Candian Infoway and Myths

Ref: http://www.itbusiness.ca/it/client/en/Home/News.asp?id=40138&bSearch=True)

Canadian Infoway which aims to have a nationwide EHR by 2009 has recommended vendors to use version 3.0 in its blueprint. In 2006 The Association of health technologies industry (AITS) and the Canadian Health Information Technology Trade Association (CHITTA) have issued a position paper to Canada Health Infoway urging the agency to reconsider its support of Health Level 7 (HL7) Version 3. The paper calls instead for Infoway to endorse HL7v2.5, which the associations say provides greater interoperability.

This is old news but the reason why i felt compelled to blog on this issue is the following presentation which is a more recent one on the infoway site
http://sl.infoway-inforoute.ca/downloads/HL7_CAN_Address_to_CRIM-AITS_October_2006_Final.pdf

Slide- 44
Myth #1• Interoperability on a large scale is possible with HL7 V2

Reality

• There is no common, pan-Canadian V2 standard

• No organization in North America is using V2.5

• The optionality in V2 inhibits (and in many cases, practically prevents)interoperability• V2 messages are designed for point-to-point systems integration, and donot easily support reuse and replication

• We need computable semantic interoperability in order to be successful withour agenda. HL7 V3 has the information model, robust data types,terminology bindings and a robust modeling methodology which support ourneeds …. and V2 does not

My Comment :Well i dont understand the concept of pan-canadian understandard. One of the biggest advantage of HL7V2.x is getting different versions of HL7V2.x interoperate with one another. The rules for compatibility between different versions (e.g. V2.3.1, V2.4 and V2.5) have been documented in the specifications. These rules describe the transmission and receipt of messages and converting their contents to data values with full backward compatibility between all 2.x versions of HL7.

So is it not better to use V2.x and force and constrain systems vendors and organisations on issues of optionality and using standard codesets rather than using V3.0

The next point is a bit contentious where it is said there is no "No organization in North America is using V2.5" by that standards then there are no organisations in N.America which use V3.0. Apart from this Biosurveillance Technical Committee in US which submitted its selected standards Healthcare Information Technology Standards Panel did endorse HL7V2.5 as one of the for use in construction of the Interoperability.

V2 messages are designed for point-to-point systems integration,this is a statement which is highly debatable considering the fact that several organisations which adopted middleware based integartion-EAI or SOA use V2.x.

The statement that "HL7 V3 has the information model, robust data types,terminology bindings and a robust modeling methodology which support ourneeds" is right to some extent but given the problems associated with the stability of RIM and the number of revisions it went through and the known problems of V3 messages with SNOMED-CT dimmens the context and relevance of the statement.

SLIDE-45

Myth #2
• Vendors will not commit to pan-Canadian standards and HL7 V3

Reality

• Not all vendors will or can

• Vendors are responding to the growing market demand being advanced byInfoway ... We need to grow that market demand!– Vendors also complying with standards when these are specified in RFPs, egCeRx for PEI and NL– There are V3 implementations in progress: IBM, Eclipse open source, Emergis,DeltaWare, etc

• Vendor community representatives are committed to pan-Canadianstandards so they only have to implement once and conformance test once• It’s largely not a V2 versus V3 issue. Often the challenge is XML enablementof the application, new functionality, new data requirements, newterminologies, not the V3 message syntax

My Comment:The realities quoted in it does indicate that V3 implementaions are in progress and the end result is not known. The slide also says "XML enablementof the application" is the issue not a v2 versus v3 issue ; well we do have V2.x XML encoding for which ready made adpaters are available from several vendors.

SLIDE-48

Myth #5

• All existing local standards must be replaced with pan-Canadian standards

Reality
• Example 1 – All existing HL7 messages do not need to be replaced with HL7v3 messages– V2 and V3 can co-exist, V3 can be mapped to V2, and V3 compliance can beachieved (with V2 components) with the use of brokers

• Example 2 - PoS systems are not required to update internal HL7 v2.xmessages to use the pan-Canadian standards– Pan-Canadian standards are not focused at the Departmental level but are forinteroperability with the pan-Canadian EHR or jurisdictional repositories

• We are requiring that new HL7 messages to communicate with the HIAL beimplemented in V3, not v2.x.

• Implementation of a pan-Canadian standard is most feasible when a net-newsystem is being installed, or an existing system is being enhanced.

My Comment:Well V2 and V3 co-existing is a reality and its happening as can be seen in the English NHS project where intra organisation integartion is done using V2.x and messages to national EHR is done using V3.0. But the statement that V3 compliance can be acheived with v2 components and use if brokers is really far fetched statement. The mapping or translation of v2-v3 is not defined properly nor any detailed documentation on the mapping is available. It is also a know fact that HL7 v3 is much more detailed than HL7 v2 and the trigger events in V2 and V3 are sufficiently different apart from the bussiness process which triggers those messages.

Iam not saying that HL7V3.0 is better compared to V2,0 but when making a statement to vendors to instill confidence in them atleast make a realistic and fact filled statement not a statement which hangs on a set of incorrect "Realities" .