The identification and the relationships of the concepts that are captured as recorded observations in the EHR are fundamental parts of defining the structure of the EHR. This activity complements the task of concept representation that is dealt with in the Vocabulary Issues section of this EHR Overview Segment of the Web site by describing the structural issues that involve the data elements/attributes and their inter-relationships. A data element/attribute is a class of concepts having a value set which may be either a measured value or a concept representational value (vocabulary) each term of which has common characteristics except at the most specific level of differentiation. Together the two sections will help the viewer understand the task of defining the Structure and Content of the EHR. Models will help represent structure and assist in understanding concept relationships. One simple EHR model consists of: Patient ID, Date-time and a list of observations. The context issues in this representation do not yield the full meaning and so several models are needed to guide the implementation of a useful system.

One of the activities that is used in standardization activities, as well as by each Acquirer who intends to use an EHR within his/her enterprise, is to create “models”. ”. In particular, we will be using the discussion about modeling to probe the concept relationships for the EHR information subdomains shown in the figure under EHR Significance. Models are representations of concepts and their inter-relationships within an information domain (i.e. a subject area of interest). At the viewer’s current level of interest in this topic, it must be clearly understood that modeling is just a way of representing all of the detailed concepts that each healthcare practitioner uses in doing his/her day-to-day job. Models represent those key aspects that are an essential general (usually graphic) representation of each of those concepts so that the practitioner can grasp a larger “Enterprise View” of the use of those concepts by other participants in healthcare. This representation is intended to lead to the individual’s application of the multiple implications of each concept in both patient care and resource management. Modeling can also be used for vocabulary issues as well as for structural issues.  Depending upon the nature of the area of interest, different techniques, each with its own notation, may be used. In the development of health informatics standards by Standards Developer Organizations (SDOs), techniques of Data Modeling and Activity/Process Modeling are both used. A Guide to the use of general modeling techniques in Healthcare (ASTM E-2145, Ref B4) is just available. For messaging, HL7 provides a Guide “Framework for Message Development” (Ref C3) that can be used to relate EHR structures to data fields used for interchange. The idea of a “Framework” for Modeling is discussed in the ASTM Practice E-2145 and also separately in the new ASTM Guide E-2118 “Guide for Coordination of Clinical Laboratory Services in an EHR Environment and Networked Architectures”. Frameworks organize the foci of interest into a matrix form. In the Information Systems Architecture (ISA) Framework (ref A11), John Zachman (www.zifa.com)   uses the nature of focus and level of specificity as rows and columns of the matrix. These axes applied to health informatics standards and to laboratory services are given in the two ASTM Standard Guides above but, in general, the following matrix, developed by Mark Diehl, DDS for ANSI HISB, gives the dimensions that the viewer needs to consider in approaching enterprise information architectures for healthcare.. Such a situation requires every healthcare enterprise to master the knowledge and skills needed to manage information architectures. This section will point to references that may be useful to the individual enterprise. Consult http://www.markdiehl.com for a broad perspective on this process.