Replacing the execution context of Arden2ByteCode means providing a class that serves as information gateway to the “outer environment” of a Medical Logic Module. Thus, via an execution context, you can integrate Arden2ByteCode into your data infrastructure.
Any execution context should be a subclass of the abstract class arden.runtime.ExecutionContext. Also a class arden.runtime.BaseExecutionContext exists, providing the ability to look up and call MLMs from the classpath. Cyclic or delayed calls are possible if an arden.EventEngine is provided to the BaseExecutionContext.
The following methods of arden.runtime.ExecutionContext may be overridden:
public DatabaseQuery createQuery(MedicalLogicModule mlm, String mapping)
This method is called when a READ statement like READ LAST 3 FROM {SELECT * FROM person} in a MLM (Medical Logic Module) is executed.
The string mapping contains whatever the braces of the read statement contain (SELECT * FROM person as of the example). These strings are specific to the environment the MLM is attached to. In the above example, SQL syntax is used, because Arden2ByteCode provides an execution context where the mapping is passed to a JDBC SQL driver specified by the user. You may use the mapping string for whatever information you need to pass from the MLM to the execution context.
The MLMs variables can be accessed via the mlm parameter, e.g. mlm.getValue("eventtime").
public ArdenValue getMessage(MedicalLogicModule mlm, String mapping)
This method is called when a message is assigned using the MESSAGE statement.
Example: msg := MESSAGE {pneumonia};
public ArdenValue getMessageAs(MedicalLogicModule mlm, String mapping, ObjectType type)
This method is called when a message is assigned using the MESSAGE AS statement.
Example:
Patient := OBJECT[name, date_of_birth];
msg := MESSAGE AS Patient {MR-111-1111};
public ArdenValue getDestination(MedicalLogicModule mlm, String mapping)
This method is called when a destination is assigned using the DESTINATION statement.
Example: dest := DESTINATION {email: email@example.com};
public ArdenValue getDestinationAs(MedicalLogicModule mlm, String mapping, ObjectType type)
This method is called when a destination is assigned using the DESTINATION AS statement.
Example:
Email := OBJECT[subject, text];
dest := DESTINATION AS Email {email: email@example.com};
public ArdenEvent getEvent(MedicalLogicModule mlm, String mapping)
This method is called when an event is assigned using the EVENT statement.
For example: patient_admission := EVENT {patient admission};
public ArdenRunnable findInterface(MedicalLogicModule mlm, String mapping)
This method is called, when an interface is referenced using the INTERFACE statement.
Example: web_service := INTERFACE {my web service};
The returned arden.runtime.ArdenRunnable acts as a proxy for an external program or service.
public MedicalLogicModule findModule(String name, String institution)
This method is run, when another MLM is referenced in the data slot using the MLM statement.
Example: find_allergies := MLM 'find_allergies' FROM INSTITUTION "my_institution";
In the above example, find_allergies is the module name string and my_institution is the institution string.
public MedicalLogicModule[] findModules(ArdenEvent event)
This method is run before an event is called in the logic slot. It should return all MLMs that are directly (no delay) evoked by the event.
Example: collected_results := CALL an_event WITH 1,2,3;
public ArdenTime getCurrentTime()
This method is called, whenever CURRENTTIME is used in a MLM.
public void write(ArdenValue message, ArdenValue destination, double urgency)
This method is called when a message is written in the action slot using the WRITE statement. The urgency is defined in the MLMs urgency slot.
Example: WRITE "hello" AT dest;
Here, message would be "hello" and destination would be the destination, which was created previously created with a line like dest := DESTINATION {email: email@example.com};.
public void call(ArdenRunnable mlm, ArdenValue[] arguments, ArdenValue delay, Trigger trigger, double urgency)
This method is called, when an MLM CALL statement is executed in the action slot. The trigger parameter can be used to calculate the called MLMs EVENTTIME and TRIGGERTIME.
Example:
other_mlm := MLM 'other';
CALL other_mlm WITH 2, TRUE, "xyz" DELAY 5 minutes;
public void call(ArdenEvent event, ArdenValue delay, double urgency)
This method is called, when an event CALL statement is executed in the action slot.
Example:
my_event := EVENT {custom event};
CALL my_event DELAY 1 week;
The classes arden.runtime.BaseExecutionContext, arden.runtime.StdIOExecutionContext and arden.runtime.JDBCExecutionContext provide examples of how to implement these methods.
If you try to attach a MLM to a certain database or any other datasource, you can for example override the createQuery() method and pass the parameters to your database query parser.
The write(), getMessage() and getDestination() methods are intended to inform the user of MLM messages. They could be implemented to display information on a GUI or web interface.
findModule() and findInterface() can serve as interface to your IT infrastructure meaning you can load programs written in other languages than Arden Syntax as well if you want that.
To use Arden2ByteCode’s command line interface for the new execution context, add it to the arden.MainClass#createExecutionContext() method.
This allows running simple MLMs directly, as well as using the arden.engine.EvokeEngine and listening to events on a port. An argument string can be passed to it via the --environment option.