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By Adron Hall on September 23, Recently I sat down to work up a solution around a rules engine. There were a few things I noticed right off. At this point I realized I had X, Y and Z reason to use it and would just have to persevere with all of the threats that are inclusive of implementing a rules engine. Sometimes one just has to step into the realm of scary and get it done. Nools is a business rules engine based on the Rete Algorithm , something that is helpful to read up on when implementing. The main deployment for nools is to a Node. So before moving on here are a few key words. The first thing I tried to run was a simple little sample of a nools rule file using the DSL. The nools file I named helloworld.
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Rules Engines can be a very valuable part of an overall business automation and decision making system. In discussing rules engines the simple view is that it is a system that uses rules, in any form, applied to data to produce outcomes. For this tutorial we will be talking about a specific implementation of the Rete algorithm pronounced as two syllables, reh-te.
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Nools is a rete based rules engine written entirely in javascript. Or download the source minified. When using nools you define a flow which acts as a container for rules that can later be used to get a session. In the above rules file we make use of a Person class and a logger. In order for nools to properly reference the Class and logger you must specify them in your options. A session is an instance of the flow that contains a working memory and handles the assertion, modification, and retraction of facts from the engine. Note assert is typically used pre engine execution and during the execution of the rules. To get a list of facts currently in the session you can use the getFacts method exposed on a session. You may also pass in a Type to getFacts which will return facts only of the given type. When you get a session from a flow no rules will be fired until the match method is called.
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GitHub is home to over 50 million developers working together to host and review code, manage projects, and build software together. If nothing happens, download GitHub Desktop and try again. If nothing happens, download Xcode and try again. If nothing happens, download the GitHub extension for Visual Studio and try again. C2FO is no longer maintaining this project. Please use accordingly. If you would like to help maintain or take over the project please let us know. Nools is a rete based rules engine written entirely in javascript.

Or download the source minified. When using nools you define a flow which acts as a container for rules that can later be used to get a session. In the above rules file we make use of a Person class and a logger. In order for nools to properly reference the Class and logger you must specify them in your options. A session is an instance of the flow that contains a working memory and handles the assertion, modification, and retraction of facts from the engine.

Note assert is typically used pre engine execution and during the execution of the rules. To get a list of facts currently in the session you can use the getFacts method exposed on a session.

You may also pass in a Type to getFacts which will return facts only of the given type. When you get a session from a flow no rules will be fired until the match method is called. The match method also returns a promise that is resolved once there are no more rules to activate. You may also run the engine an a "reactive" mode which will continue to match until halt is invoked. In the following example the rules engine continues to evaluate until the counter reaches If you remove the "counted to high" rule then the engine would run indefinitely.

When working with a lot of facts it is wise to call the dispose method which will purge the current session of all facts, this will help prevent the process from growing a large memory footprint. To check if a flow currently is registering with nools use the hasFlow function;. The agenda manages a stack of agenda-groups that are currently in focus. The default agenda-group is called main and all rules that do not have an agenda-group specified are placed into the main agenda-group.

As rules are fired and a particular agenda-group runs out of activations then that agenda-group is popped from the internal agenda-group stack and the next one comes into focus. This continues until focus is explicitly called again or the main agenda-group comes into focus. Note Once an agenda group loses focus it must be re-added to the stack in order for those activations to be focused again.

In the above rules we have defined two agenda-groups called ag1 and ag2. When running your rules and you want a particular agenda group to run you must call focus on the session of the flow and specify the agenda-group to add to the stack.

Notice above that the last agenda-group focused is added to the array first. Sometimes you may want an agenda-group to auto-focus whenever a certain rule is activated. In the above rules we created a state machine that has a rule with auto-focus set to true. When declaring a flow it is defined with a default conflict resolution strategy.

A conflict resolution strategy is used to determine which rule to activate when multiple rules are ready to be activated at the same time. The default conflict resolution strategy consists of salience and activationRecency.

In the above example activation 2 would be fired since it is the most recent activation and the rule salience is the same. To override the default strategy you can use the conflictResolution method on a flow. The combination of salience , factRecency , and activationRecency would do the following. In Example 3 activation 2 would fire because salience and factRecency are the same but activation 2's activation recency is greater. Salience is an option that can be specified on a rule giving it a priority and allowing the developer some control over conflict resolution of activations.

In the above flow we define four rules each with a different salience, when a single message is asserted they will fire in order of salience highest to lowest. Constraints define what facts the rule should match. The constraint is a array of either a single constraint i.

Bootstrap rule or an array of constraints i. Pattern optional - The pattern that should evaluate to a boolean, the alias that was used should be used to reference the object in the pattern. Strings should be in single quotes, regular expressions are allowed. Available operators are. Reference optional - An object where the keys are properties on the current object, and values are aliases to use. The alias may be used in succeeding patterns.

When declaring your rules progrmmatically you can also use a function as a constraint. The function will be called with an object containing each fact that has matched previous constraints. The not constraint allows you to check that particular fact does not exist. The previous example will check that for all numbers in the workingMemory there is not one that is greater than n1. The previous example will evaluate to true if you have a string in workingMemory that equals hello , world, or 'hello world. The or constraint can be combined with a not constraint to allow for the checking of multiple not conditions without the implcit and.

Note Using the or with a not will cause the activation to fire for each not condition that passes. In the above examples if none of the three facts existed then the rule would fire three times. The from modifier allows for the checking of facts that are not necessarily in the workingMemory. The from modifier can be used to access properties on a fact in workingMemory or you can use javascript expressions. To access properties on a fact you can use the fact name and the property you wish to use as the source for the from source.

The above example will used the address, firstName and lastName from the person fact. For example assume the person object from above has friends that are also of type Person.

The above example will pull the friend fact from the friends array property on fact p , and first from the friend 's firstName. You could achieve the same thing using the following code if you assert all friends into working memory.

It checks for the existence of a fact in memory. Assuming the above constraint. The following facts would cause the rule to fire once since there is a number that is greater than 1. The action is a function that should be fired when all patterns in the rule match. The action is called in the scope of the engine so you can use this to assert , modify , or retract facts. An object containing all facts and references created by the alpha nodes is passed in as the first argument to the action.

So calculate's action modifies f3 by adding the value of f1 and f2 together and modifies f3 and retracts f1. For rules defined using the rules language nools will automatically determine what parameters need to be passed in based on what is referenced in the action.

If your action is async you can use the third argument which should be called when the action is completed. Globals are accessible through the current working scope of rules defined in a dsl , very similar to using the scope option when compiling. Note globals are not part of the working memory and therefore are not accessible in the LHS when or your rule.

The import statement allows you to import other nools files into the current one. This can be used to split up logical flows into small reusable groups of rules. Create a rules file which imports the define. Now we can use orRule. Note nools will handle duplicate imports, in this case define.

Nools can also be used in the browser. The only difference is that you cannot pass a file location to the compile method instead you must provide the source. You may also use the nools executable to compile source into a browser friendly format skipping the need for compiling each time.

If you import the flow using a script tag you can get a reference to the flow by using nools. You may also specify the name of the flow when compiling, it defaults to the name of the nools file less ". If you are using requirejs or nools must be required using something other than require "nools" then you can specify a location of the nools source. Examples of using nools with require js are located in the examples directory. Skip to content. Rete based rules engine written in javascript noolsjs.

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