Code Generation: Rule Engine

The purpose of this repository is to provide an example of how a Rule Engine can be implemented in InterSystems Caché using Object Generators.

Implementation

• Code generation is an excellent way of increasing performance moving run-time calculations to compile-time.
• The intention of this example is to explain how something as complex as a Rule Engine can be modelled in InterSystems Caché.
• InterSytems Ensemble provides a very powerful Rule Engine that is way much better than this homemade example.

Goal

1. Describe a rule using a human-readable XML.
2. Compile the rule and generate the code to evaluate that rule in run-time.

Classes

Installation

set path="C:\Temp\cache-iat-ruleengine-master\cache"
do $system.OBJ.ImportDir(path,"*.inc","ck",.error,1)
do $system.OBJ.ImportDir(path,"*.xml","ck",.error,1)

Run the code

• The example provides a patient alert rule.
• After compiling the classes of the project, we can run the example:
  • Create a context to evaluate the rule: this context contains all needed data to evaluate the rule, in this case a patient object.
  • Evaluate the rule.
• To run the example, simply execute ##class(IAT.RuleEngine.Test.Examples).Run() method

Class IAT.S01.Rules.Test.Example Extends %RegisteredObject
{
ClassMethod Run() As %Status

{

set ret = $$$OK

try {

// create a patient

set p = ##class(Patient).%New()

set p.MRN="1234", p.Name="John", p.Surname="Snow", p.DOB=$zdh("1975-05-07",3)
// create a rule context, set data
set context = ##class(PatientContext).%New()
set context.Patient = p

// evaluate Patient Alerts Rule
set ruleEngine = ##class(IAT.S01.Rules.Engine).%New()
$$$TOE(sc, ruleEngine.Evaluate("IAT.S01.Rules.Test.PatientAlertsRule", context, .log))

// print log
write !,"Rule log:",!
zwrite log

} catch ex {

set ret = ex.AsStatus()

do $system.Status.DisplayError(ret)

}

quit ret

}
}

Execute the method from a Terminal session:

do ##class(IAT.RuleEngine.Test.Example).Run()
=======================

SendEmail

To:test@server.com

Body:

Patient is so old!
=======================

ShowObject

+----------------- general information ---------------

|      oref value: 1

|      class name: IAT.RuleEngine.Test.Patient

| reference count: 3

+----------------- attribute values ------------------

|                DOB = 49069

|                MRN = 1234

|               Name = "John"

|            Surname = "Snow"
Rule log:

log=4

log(1)="[2016-02-22 16:29:44] Rule: Not young anymore!"

log(2)="[2016-02-22 16:29:44] Action: 1"

log(3)="[2016-02-22 16:29:44] Action: 2"

log(4)="[2016-02-22 16:29:44] Action: 3"

Developer Community

Have a look at InterSystems Developer Community to learn about InterSystems technology, sharing solutions and staying up-to-date on the latest developments.

This example was published in https://community.intersystems.com/post/object-generators-homemade-ruleengine

Contributions

%XGEN.AbstractDocument implementation

Dmitry Maslennikov (https://github.com/daimor) has uploaded a very interesting alternative approach which uses %XGEN.AbstractDocument class to process the XData.

The code is available in /pr/xgen branch.

Additional information is available here: https://community.intersystems.com/post/xdata-studio-asist