Arden Syntax

for Medical Logic Systems

Introduction

Arden syntax is a grammar for describing medical conditions and recommendations, used in Medical algorithms. It is a Health Level 7 / ANSI standard that can be used to encode computable knowledge. The Arden Syntax specification covers the sharing of computerized health knowledge bases among personnel, information systems, and institutions.
Arden Syntax arose from the need to make medical knowledge available for decision making at the point of care. It can also be described as a standard, formal procedural language that represents medical algorithms in clinical information systems as knowledge modules; Medical Logic Modules (MLMs).

Brief History:

Arden syntax was first introduced in 1989 at the Arden Homestead Conference in Harriman, NY, where it took its name. Arden Syntax for Medical Logic Systems v1.0 was adopted by ASTM in 1992. The second version (v2.0) was adopted by ANSI and HL7 in August, 1999. The developed and maintenance of the standard is overseen by the HL7 Arden Syntax Special Interest Group (Arden Syntax SIG) and the Clinical Decision Support Technical Committee, too.

Description of Arden Syntax for Medical Logic Systems:

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 modeled by chaining a sequence of MLMs.
The initial version of the Arden Syntax was based largely on the encoding scheme for generalized 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.
MLM Writer: An Integrated Development Environment for Creating Arden Syntax Medical Logic Modules


Benefits / Advantages of using Arden syntax:

Arden syntax was specifically developed for health care applications, and for embedding MLMs into clinical information systems.

+ It allows knowledge sharing within and between institutions. The Arden syntax has the clinician as a target user. 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.
+ It makes medical knowledge and logic explicit. 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.
+ Standardize the way medical knowledge is integrated into hospital information systems.
+ 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.


Problems / Limitations of Arden syntax

- 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 representing 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.

About Medical Logic Modules (MLMs):

Medical Logic Module (MLM) is an independent unit in a health knowledge base. Each MLM contains sufficient logic to make a single medical decision. MLMs have been used to generate clinical alerts, interpretations, diagnoses, screening for clinical research, 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. For example, one MLM warns physicians when a patient develops new or worsening kidney failure.

MLM is very significant because it has the ability to make health decision using:
* maintenance information,
* links to other sources of knowledge/data,
* and logic.
In more detail, MLM is a stream of text stored in an ASCII file in statements called slots.
MLM Strucure
\ Each MLM is composed of three categories: maintenance, library, and knowledge. Each category is indicated by a category name followed immediately by a colon (e.g. maintenance:, library:, and knowledge:) and each category have specific slots. A space may precede the category name and follow the colon, but no space is allowed between the category name and the colon. Categories must appear in the following order, Maintenance:, Library:, and then Knowledge:.
\ Each slot within a category, consists of a slot name, followed immediately by a colon (for example, title:), then followed by the slot body, and terminated with two adjacent semicolons (;;) which is referred to as double semicolon. A space may precede the slot name and follow the colon, but no space is allowed between the slot name and the colon. The content of the slot body depends upon the slot, but it must not contain a double semicolon, except inside comments, string constants, and mapping clauses.
\ In the MLM, the categories and slots must follow the order in which they are listed in this primer, however, some slots are considered optional while others are required. . .
Here is an example of MLM in Arden Syntax


Currently Use of Arden Syntax

The Arden Syntax makes knowledge portable, but MLMs developed for one environment 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:

Healthcare organizations with Arden-compliant commercial systems include:

References and Related Links:

  1. Directory for the Standardization on Medical Informatics
  2. Automated Guidelines Implemented via the World Wide Web
  3. MLM Writer: An Integrated Development Environment
  4. The relationship between GLIF and the Arden Syntax
  5. Experiences from the Use of DSS
  6. ARDEX SYNTAX
  7. Knowledge Representation in Health Sciences
  8. OpenClinical: Arden Syntax
  9. The Arden Syntax for Medical Logic Systems