MDMI Section for Cross Paradigm Implementation Guide
What is conceptual approach of MDMI?
Model Driven Message Interoperability (MDMI) is a software model developed by a group of experts to
reduce the costs of moving and transforming of data in one message format into a different message
format while also providing an approach to reduce the time and effort of maintaining and enhancing
these transformations. Various technical approaches were considered and these experts determined
that a model driven approach was the best to achieve the objectives; hence the name Model Driven
Message Interoperability.
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MDMI is both an OMG standard and a software package available from OHT which implements
the MDMI standard.
MDHT is something totally different. We won’t discuss it in this document. Out of scope.
In the first part, we are talking about the MDMI standard, and in the 2nd part we are talking
about the MDMI software.
At some transitional point, we would say it’s only practical to use MDMI standard if you have a
software tool. In the remaining document, we use MDMI tool to illustrate how this is done.
The MDMI contains two key core concepts. The first is the MDMI Model. The MDMI model is a metamodel that can be used to define a MDMI model for any specific data or message format. The second is
the MDMI Referent Index. The MDMI Referent Index is a list of atomic, semantically clear and distinct
terms that represent all the terms (vocabulary) in a specific domain or industry.
The MDMI meta-model itself contains three distinct sub-models. One sub-model is for the syntax of the
data format. The Syntax Sub-model is used to decompose a source message into its semantic elements
or to construct the semantic elements of the target message into the correct syntax. The Semantic submodel insures one can create and populate clear, atomic, distinct Semantic Elements for each data
element contained in a message. The third sub-model is used for mapping of the Semantic Elements to
the semantic terms (called Business Elements) in the Referent Index.
The Referent Index contains the list of terms, almost like words, that can be exchanged in an industry.
The terms in the Referent Index provide the semantic link between the data elements in the source
message and the data elements in the target message. The process MDMI uses to exchange information
from one format to another is to decompose the source message into its semantic elements, move the
value of the semantic element into the semantic element of the target message and then recompose
the target message into the correct syntax for that message. The keystone to this approach is the
Referent Index.
How does MDMI work in practice?
As MDMI is based on a model driven approach, there is a design time element (populating the MDMI
meta-model for a particular message format) and a runtime element (taking the source message and
transforming it into the target message).
As stated, MDMI is an open standard from OMG. All the work done for the HL7 Cross Paradigm project
was done using tools available in the Open Health Tools (OHT) MDMI project. These tools implement
and are compliant with the OMG MDMI Standard. It is well beyond the scope of this implementation
guide to document implementing the OHT MDMI tools. The remainder of this section of the
implementation guide uses the OHT MDMI open source tools to implement information exchange
between two data formats.
To populate the MDMI Model for a specific format, we used the MDMI Editor. This is a graphical tool.
One fills out the appropriate fields that describe the syntax sub-model, the semantic sub-model, and the
link between the semantic elements and the Referent Index. When this process is complete, the user
“saves” the instance of the model as a MDMI Map. A MDMI map is a computable file that is used by the
MDMI runtime tool in the actual transformation process.
It is to be noted, that the MDMI Map is specific to a particular message format. For the Cross Paradigm
project, we created MDMI maps for the Consolidated Clinical Document Architecture (CCDA), for HL7
V2, and for FHIR. Each map was developed independently because any MDMI Map can exchange
information with any other MDMI map that uses the same Referent Index. We could have built an
MDMI map for a proprietary format and therefore that map could be used with CCDA, HL7V2, and the
FHIR maps.
The OHT MDMI Runtime was used to actually move and transform from one HL7 paradigm (e.g. HL7V2
to FHIR). The runtime is a Java service with an API with four three inputs; the source message, the
source MDMI map, and the target MDMI map. The result of this process is a target message or file.
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How is MDMI made real in the healthcare?
MDMI was developed to solve interoperability in any industry. To make it useful in healthcare, a
Referent Index for needed to be developed. Because MDMI is generic and standards based, in creating
a Referent Index for the Healthcare Industry existing standards are leveraged and used. The Referent
Index has four key data elements for each term: a name, a description, a datatype, and a uniqueId. The
MDMI Referent Index for healthcare leveraged the HL7 Datatypes and Vocabulary to determine the
appropriate granularity of the terms in healthcare RI as well as work done in data dictionaries by the C154 working group and other HL7 documentation.
A MDMI Referent Index for Healthcare has been developed that supports all the data elements required
by US Meaningful Use Stage 2. The MDMI Referent Index for Healthcare, as well as all the maps
developed by CCDA, HL7, and FHIR available as open source maps in the OHT MDMI project.
It is important to note that the MDMI Model did not have to change in order to provide data exchange
for healthcare. As stated, to make MDMI practical for healthcare, only a Referent Index for Healthcare
was needed.
Finally, much work was done by the Cross Paradigm Group prior to working with MDMI. Much work was
done on the concept of a Common Information Model as well as spreadsheets to align data elements in
the different standard messaging formats. There is a direct correlation between the concept of the
Common Information Model and the MDMI Referent Index for Healthcare. In addition, the working
group developed a spreadsheet to help associate different data elements in the models. The MDMI
open source group has developed a simple application that generates the information for the
spreadsheet using the MDMI maps and the MDMI Referent Index for healthcare.
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