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Product Arden

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Product Brief - Arden Syntax

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Product Name

Arden Syntax


Standard Category

Health Information Knowledge Representation Standards

Integration Paradigm


Normative, ANSI/ISO Standard


  • ANSI/HL7 Arden V2.0-1999, a revision of ASTM E1460-92
  • ANSI/HL7 Arden V2.1-2002
  • ANSI/HL7 Arden V2.5-2005
  • ANSI/HL7 Arden V2.6-2007
  • ANSI/HL7 Arden V2.7-2008


The Arden Syntax for Medical Logic Modules (MLMs) is a language for representing and sharing medical knowledge among personnel, information systems and institutions. Internal programming model is based on declarative logic derived from a multitude of sources (including PASCAL, LISP, APL, PL/1, HCOM). Triggering of individual models is a hybrid of direct calling (similar to a RPC) and a production model. Oldest decision support standard. Originally developed as part of a collaborative conference and standardized under ASTM. Moved to HL7 in 1997/1998


The Arden Syntax for Medical Logic Modules (MLMs) is an ANSI-approved American National Standard language for encoding medical knowledge and representing and sharing that knowledge among personnel, information systems and institutions. It is designed for organizations that require or develop systems that automatically assist physicians in decisions and alerts. The logic for making these decisions or issuing these alerts is encoded into health knowledge bases called MLMs, each of which contains sufficient knowledge to make a single decision. Contradiction alerts, management suggestions, data interpretations, treatment protocols, and diagnosis scores are examples of the health knowledge bases that can be represented using the Arden Syntax. With an appropriate computer program (known as an event monitor), MLMs run automatically, generating advice where and when it is needed. For example, one MLM warns physicians when a patient develops new or worsening kidney failure. The American Society for Testing and Materials (ASTM) previously adopted it as document E 1460, under subcommittee E31.15 Health Knowledge Representation. Adopted by ASTM in 1992, this became Arden Syntax Version 1.0. Beginning in the summer of 1998, sponsorship of this standard was moved to Health Level Seven (HL7). The Clinical Decision Support and Arden Syntax Work Groups of HL7 oversee maintenance of the standard. Arden Syntax Version 2.0 was formally adopted by HL7 and ANSI in August 1999. The move of Arden Syntax from ASTM to Health Level Seven originated in 1997. The HL7 Clinical Decision Support Work Group first met in June 1997 and was organized by Carol Broverman. In the Summer of 1999, the Arden Syntax Standard was formally transferred from ASTM to HL7, and Version 2 of the standard was formally endorsed by HL7 and ANSI. Associated work groups have followed, including Clinical Genomics, Regulated Clinical Research Information Management (RCRIM) and Electronic Health Records (EHR). All of these groups were or are sponsored by the Clinical Decision Support Work Group. In order to make the overall work group less technology-specific, the Arden Syntax was spun off into its own work group in January, 2001, under the sponsorship of the Clinical Decision Support Work Group. Version 2.1 of the standard was formally endorsed by HL7 and ANSI during 2002. Version 2.1 introduces a structured message as an optional part of the WRITE statement. Using this structure, which is encoded using an XML DTD, authors can specify many different parameters of an output message of a decision support system in a standard fashion. These include time outs and escalation information for alerts; embedded orders; subject; and recommendation. The Arden Syntax standard is now at Version 2.7 and was approved by ANSI in December 2008. It is available in the bookstore area of the HL7 website:

Business Case (Intended Use, Customers)

  • An Open standard for representing CLINICAL knowledge, it is intended to be used by individual clinicians, institutions, and vendors to develop clinical rules (rules that directly impact patient care) using a standard format and language. Arden Syntax is also suited for writing business rules that directly interface with clinical data.


  • Allows for distributed development and sharing of development costs among institutions in addition to the dissemination of clinical knowledge.

Implementations/ Case Studies (Actual Users)

  • Commercial vendors:
    Medexter Healthcare GmbH
    Siemens Medical Systems
  • Institution-specific systems:
    Columbia University


  • Tutorials have been offered.

Work Groups


Certification Available
  • none


Relationship to/ Dependencies on, other standards

  • None currently. Exploring use of following standards / drafts / works in progress: DSS DSTU (SOA), vocabulary standards (e.g. SNOMED), emerging virtual medical record, GELLO

Links to current projects in development