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Methods and tools for the development of computer-interpretable guidelines

Arden Syntax
Standard, formal procedural language that represents medical algorithms in clinical information systems as knowledge modules (Medical Logic Modules (MLMs))
keywords Clinical decision support, computer-interpretable guidelines, knowledge representation, Medical Logic Modules, MLMs, ANSI, HL7, ASTM
developed by Maintenance of the standard is overseen by the HL7 Arden Syntax Special Interest Group and the Clinical Decision Support Technical Committee.
introduced First introduced in 1989 at the Arden Homestead Conference in Harriman, New York. Arden Syntax for Medical Logic Systems Version 1.0 was adopted by ASTM in 1992. Version 2.0 was adopted by HL7 and ANSI in August, 1999.
status In use / under continued development.

The latest version of Arden is 2.1 - certified as an ANSI standard in December, 2002.
support Sponsored by HL7 since 1999.
in use The Arden Syntax makes knowledge portable, but MLMs developed for one environment are are not easily embeddable within another. Most commercial applications incorporating MLMs are developed by individual vendors primarily for use within their own environments. Vendors who have developed Arden-compliant decision support applications include:
  • Eclipsys Corporation
  • McKesson Information Solutions
  • Siemens Medical Solutions Health Services Corporation
  • MICROMEDEX (MICROMEDEX® Medical Logic Modules).

Healthcare organisations with Arden-compliant commercial systems include:
  • Alamance Regional Medical Center, Burlington, NC (Eclipsys)
  • Sarasota Memorial Hospital, Sarasota FL (Eclipsys)
  • Columbia-Presbyterian Medical Center, New York, NY (developed with IBM)
  • JFK Medical Center, Edison, NJ (McKesson)
  • Covenant Health, Knoxville, TN (McKesson)
  • St. Mary's Hospital, Waterbury, CT (McKesson)
  • Mississippi Baptist Health Systems, Jackson, MS (McKesson)
  • St. Vincent's Hospital, Birmingham, AL (McKesson)
  • St. Mary's Medical Center, Knoxville, TN (McKesson)
  • Meridian Health Systems / Jersey Shore Medical Center, Neptune NJ (Siemens)
  • Ohio State University, Columbus OH (Siemens)
tools  bullet  Medical Logic Module Library  bullet  MLM syntax checker for Windows
The Arden Syntax for Medical Logic Systems encodes medical knowledge in knowledge base form as Medical Logic Modules (MLMs). An MLM is a hybrid between a production rule (i.e. an "if-then" rule) and a procedural formalism. Each MLM is invoked as if it were a single-step "if-then" rule, but then it executes serially as a sequence of instructions, including queries, calculations, logic statements and write statements.

Arden was developed for embedding MLMs into proprietary clinical information systems. It was designed to support clinical decision making in particular: an individual MLM should contain sufficient logic to make a single medical decision. Sequencing tasks can be modelled by chaining a sequence of MLMs. MLMs have been used to generate clinical alerts and reminders, interpretations, diagnoses, screening for clinical research studies, quality assurance functions, and administrative support.

With an appropriate computer program (known as an event monitor), MLMs run automatically, generating advice where and when it is needed, e.g. to warn when a patient develops new or worsening kidney failure.

The initial version of the Arden Syntax was based largely on the encoding scheme for generalised decision support used in the HELP (Health Evaluation through Logical Processing) system for providing alerts and reminders, developed at the LDS hospital in Salt Lake City.

  • The target user of the Arden Syntax is the clinician. The Arden Syntax is not a full-feature programming language; for example, it does not include complex structures. MLMs are meant to be written and used by clinicians with little or no programming training.
  • Arden provides explicit links to data, trigger events and messages to the target user. It clearly defines the hooks to clinical databases, and defines how an MLM can be called (evoked) from a trigger event.
  • The Arden Syntax brings particular support for time functions. Almost all medical knowledge involves the time that something happened. Arden ensures that every data element and every event has a data/time stamp that is clinically significant. Many time functions are provided to help users specify the date and time in MLMs. With any other language, these definitions would be more dependent on the person implementing the MLM; the Arden Syntax allows them to be defined explicitly .

  • limitations

    The basic format of Arden Syntax, the MLM, means that it is not the most appropriate format for developing complete electronic guideline applications.

    A problem that occurs with any form of clinical knowledge representation is the need to interact with a clinical database in order to provide alerts and reminders. Database schemata, clinical vocabulary and data access methods vary widely so any encoding of clinical knowledge (such as a MLM) must be adapted to the local institution in order to use the local clinical repository. This hinders knowledge sharing. Arden is the only standard for procedurally representating declarative clinical knowledge (contrast GLIF or PROforma, for example, which are more declarative formats), so this problem is associated with Arden, but it is not unique to it.

    Arden explicitly isolates references to the local data environment in curly braces ["{}"] in a MLM, often referred to as the "curly braces problem". Efforts are underway in HL7 to help solve this problem, but it is not something that the Arden workgroup can do alone; it requires industry-wide standardization.

    Another potential limitation of Arden is that it does not explicitly define notification mechanisms for alerts and reminders. Instead, this is left to local implementation and is, like database queries, contained in curly braces in a MLM. Explicit notification mechanisms in the Syntax itself may be a part of a future edition.

    " Arden Syntax for Medical Logic Systems v2.1 (reflects changes incorporated by the Technical Committee up to and including September, 2000) "

    [HL7 bookstore]

    " This specification covers the sharing of computerized health knowledge bases among personnel, information systems, and institutions. The scope has been limited to those knowledge bases that can be represented as a set of discrete modules. Each module, referred to as a Medical Logic Module (MLM), contains sufficient knowledge to make a single decision. Contraindication alerts, management suggestions, data interpretations, treatment protocols, and diagnosis scores are examples of the health knowledge that can be represented using MLMs. Each MLM also contains management information to help maintain a knowledge base of MLMs and links to other sources of knowledge. Health personnel can create MLMs directly using this format, and the resulting MLMs can be used directly by an information system that conforms to this specification. "

    Jenders RA, Corman R, Dasgupta B. Making the standard more standard: a data and query model for knowledge representation in the Arden syntax. AMIA Annu Symp Proc. 2003;:323-30.

    [PubMed]   []

    " CONTEXT: Arden Syntax is a Health Level Seven (HL7) standard that can be used to encode computable knowledge. However, dissemination of knowledge is hampered by lack of standard database linkages in Arden knowledge bases (KB). Moreover, the HL7 Reference Information Model (RIM) is object-oriented and hence incompatible with the current Arden data model. Also, significant investment has been made in Arden KBs that would be lost if a backward-incompatible data model were adopted. OBJECTIVE: To define a data model that standardizes database linkages and provides object-oriented features while maintaining backward compatibility. ANALYSIS: We identified the objects of the RIM that could be used as a schema for standard database queries. We propose extensions to Arden to accommodate this model, including the manipulation of objects. CONCLUSION: A data model that standardizes database linkages and introduces object-oriented constructs will facilitate knowledge transfer without violation of backward compatibility in the Arden Syntax. "

    Hripcsak G, P. Ludemann, T.A. Pruor, O.B. Wigertz, P.B. Clayton. Rationale for the Arden Syntax. Computers in Biomedical Research, 27 (4), 291-324, 1994.


    " The Arden Syntax, a language designed for writing and sharing task-specific knowledge for Medical Logic Modules (MLMs), has been recently accepted as a standard by the ASTM. The syntax is concerned with the critical task of sharing medical knowledge bases across many institutions. Because of the relative lack of agreement on vocabularies and data standards and because of the many other obstacles, the developers of the Arden Syntax took a pragmatic, straightforward approach that has borne fruit in a very short period of time. The syntax provides a vehicle for the health care community to begin sharing, so that we can see what works and what does not work, and we can begin to address the critical obstacles. In designing a language like the Arden Syntax, the authors make many decisions--but the final document gives only the result of these decisions without any explanation. By writing down the rationale behind the design of the syntax, we hope to aid users of the language, implementors of the language, and future designers of new languages. "
    Hripcsak G. Tutorial on how to use the Arden Syntax. Writing Arden Syntax medical logic modules. Computers in Biology and Medicine 1994;24(5):331-63 (Issue dedicated to the Arden Syntax)


    " The Arden Syntax for Medical Logic Modules is a language for encoding medical knowledge bases that consist of independent modules. The Arden Syntax has been used to generate clinical alerts, diagnostic interpretations, management messages, and screening for research studies and quality assurance. An Arden Syntax knowledge base consists of rules called Medical Logic Modules (MLMs), which are stored as simple ASCII files that can be written on any text editor. An MLM is made of slots grouped into three categories: maintenance information, library information, and the actual medical knowledge. Most MLMs are triggered by clinical events, evaluate medical criteria, and, if appropriate, perform an action such as sending a message to a health care provider. This paper provides a detailed tutorial on how to write MLMs. "

    Pryor TA, Gardner RM, Clayton PD, Warner HR. The HELP system. J Med Syst 1983 Apr;7(2):87-102

    [PubMed]   []

    " "

    Gardner RM, Pryor TA, Warner HR. The HELP hospital information system: update 1998. Int J Med Inf. 1999 Jun;54(3):169-82.

    []  []

    contact Dr. Robert Jenders
    Department of Medicine
    Cedars-Sinai Medical Center & University of California, Los Angeles
    8700 Beverly Boulevard, SSB-309
    Los Angeles, CA 90048-1804

    links  bullet  Arden Syntax website (at Cedars-Sinai Medical Center, Los Angeles)  bullet  Arden Syntax v2.1 [HL7 bookstore]  bullet  A Gentle Introduction to Arden Syntax - presentation by R.M. Sailors, University of Texas  bullet  HL7 - Health Level 7  bullet  American National Standards Institute (ANSI)  bullet  American Society for Testing and Materials (ASTM)  bullet  Eclipsys Corporation  bullet  McKesson Information Solutions  bullet  Siemens Medical Solutions Health Services Corporation  bullet  MICROMEDEX  bullet  Micromedex White Paper: Medical Logic Modules by John Dulcey (2002)  bullet  Demonstration of Micromedex commercial Medical Logic Modules product
    Robert Jenders, Cedars-Sinai Medical Center & University of California, Los Angeles
    page history
    Entry on OpenClinical: 2002
    Last main updates: 08 June 2004; 30 March 2005


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