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How to build a rules engine

How to build a rules engine

Net is a rules engine, as you guessed probably based on the name! Net was born out of a discussion I had at my workplace. In order to define rules for a certain class or instance, all you have to do is decorate the class with pre-defined rule attributes. The basic usage section will get you started.

And, it does not end there. Check out the sections after the basic usage section to know more! Net can be used in console, web applications or anything else for that matter. The sample included uses an MVC project to demonstrate how to use this library. DataAnnotations namespace see Using data annotations. To install SimpleRules. Net from NuGet, run the following command in the package manager console or from the nuget user interface.

Before we get on with anything, I would like to define some terminology that will be used across this file.

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Consider the snippet below:. In the above class the property that is decorated with the EqualTo attribute will be referred to as the "source" and the property identified by the argument to this attribute Password in this case will be referred to as the "target". For any source there could be multiple targets i. Lets say you have a User object and you need to validate if the Password property matches the ConfirmPassword property and also if the EmailAddress and PhoneNumber properties match their appropriate pattern, as suggested by their names.

Here is what you could do:.

Building a rule engine in c#

As evident from the snippet above, all you had to do was decorate the ConfirmPassword property with the EqualTo attribute, by passing in the name of the property that has to be matched with, in this case Password. With this done, when you have an instance of user, it can be validated as shown below:.

An illustration is shown below:. The result will be a ValidationResult that contains an Errors property with 3 errors in this case - one each for mismatching passwords, invalid email address and invalid phone number.

In the next section, you will see how the rule metadata can be seperated out of the class to keep the entities and the rules separate, in order to achive loose coupling. One important thing to note is that when a rule is applied on a certain property the sourcethe data types of the "target" property or properties should match that of the source. This is applicable when validating against a constant too. In the earlier section you saw how easy it is to setup and run a validation using the SimpleRules engine.Rules occupy a hazy area between data and procedure.

Like data, each rule in a rule base is independent, and can be linked to other rules dynamically based on common values. Looking at it another way, both databases and procedures can be thought of as degenerate cases of rule bases. A database is a collection of rules that have no action statements and only one set of conditions. A procedure is one big rule with many statements. Figure 1 illustrates the relationship between data, procedure and rules.

Because most programming tools are designed for either data or procedures, when confronted with a specification written as a collection of rules, the developer is faced with a tricky problem. The rules cannot be expressed in data, and coding them procedurally leads to spaghetti code for even the best of programmers. Further the original rules get lost in the code, become difficult to debug, and almost impossible to update if necessary.

Ironically, this difficult part of an application is often its heart, and, to make matters worse, the piece most likely to change.

Consider a billing application for a phone company. Most of the application is cleanly coded using data for calls and customers, and procedures for processing the data. But pricing the call is the tricky part, based on a collection of rules derived from marketing concerns, local regulations, various sub-carriers, and special arrangements with large customers, all on top of the expected rules based on time-of-day, physical distance of call, length of call, and whether it was a credit card, collect or directly billed call.

All you need to do to understand the importance of phone call pricing is listen to the large phone company's ads. Each claims to have better pricing rules. The volatility of the rules derives from the competitive environment, evolving technology and changing government regulations. The phenomena of a difficult rule-based component being the heart and soul of an otherwise straight-forward application occurs over and over.

Consider the underwriting rules for insurance companies, the scheduling rules for an airline, the configuration rules for manufacturing, the diagnostic rules in a help desk, loan approval rules in banking, and exception handling rules in process control.

So what's a programmer to do?

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There are tools for coding rules directly, but there are two major problems with them, one related to environment and the other to the rule language itself. The environment issue is simply one of integration. Most of an application can be implementented using conventional database and programming tools.

To be practical, the rule-based component must easily become a part of the full application architecture. The rule language issue is a more difficult one. The sad truth is the rules for one problem domain are not really very much like the rules for another. It is simply not clear what a universal rule language should like. If a rule language is easy to use, then the chances are it doesn't have the power or expressibility necessary for very many application areas. If a rule language has all of the bells and whistles necessary for multiple application areas, it becomes very difficult to use.

Because of these difficulties, most programmers simply roll up their sleeves and start forcing the rules into procedural code. It is for this reason that few applications really have any heart.

There is another option, and that is to build a custom rule-engine for the application. The custom rule-engine uses a rule syntax that mates well with the problem domain, provides integration tools directly related to the application, and processes the rules in the most sensible manner. The design issues with rule engines are not dissimilar from the issues with data engines.

That is, for a program to access data two things need to happen. One, a format for the data needs to be designed, and two, software that accesses the data needs to be designed. This is true for both external data bases, which range from simple flat files to full relational systems, and internal data that can be represented in arrays, structures, linked lists or arbitrarily complex combinations of all three.

In each case the programmer picks a representation and uses either canned software or writes some new code to handle the data. Rules present the same technical challenges. A format for the rules needs to be designed, and software that provides accesses to the rules needs to be provided. As with data, there are many possibilities, depending on the situation.In this article, we discuss dynamic business rules in software development and a few approaches that can be employed to achieve this.

In most software solutions, business rules are often statically coded into the system in languages such as C. The business rules will have been captured by an analyst at one point and documented in a user story or functional specification for a developer to ingest and build code from.

If a requirement changes, the analyst typically will document this, pass the change request over to the developer for him to then build. This often involves lifting the hood on the existing codebase, making the changes and then going through a test and release cycle. Dynamic business rules allow the end-user to make changes to the way their software behaves — without developer intervention.

Download our strategy guide to start implementing dynamic business rules to your organization. The benefits of implementing dynamic business rules are obvious. Some of the reasons mentioned for implementing them are:. Dynamic business rules can free up developers to work on more interesting tasks Click To Tweet. Depending on how much configuration management is required, you have a few options:. You can use configuration tables if the business rules you need to amend are simple.

For example, you have an application that extracts the X number of records from the database for each query. The value for X could be defined in the admin section of your application and fetched at run-time thereby giving you some element of dynamic business rules. Or maybe another set of examples are the descriptions of page headers, images or text on buttons in your web application. Settings such as these can be stored in configuration tables and administered by power users on a client site.

You can keep this generic, yet simple and have a database table with a similar definition:. The unique key, e. Human readable description for the admin user, e. This is the login message the user sees. This can be used to group settings per functional area, e.

Then at runtime, you can load these settings via some kind of helper class. Integration with your existing product stack, training, licensing costs or technical support all need to be considered. Workflow Foundation integrates easily with your. NET web applications allowing you to build workflows in Visual Studio. You can easily model process flows and develop business rules through the designer canvas that ships out of the box. You can re-host the Workflow Designer in a standalone WPF application for business analysts to use on their machines.

The designer canvas offers a drag and drops user experience which is hard to beat. ActiPro has a product that helps you get around this, though. You can speak to our team too as our engineers are experts and building applications using WPF!

Naturally, you need to import your domain-specific objects and DLLs into the designer to use them, and whoever updates the workflows must know their way around the object graph and problem domain.

how to build a rules engine

With the advent of. The community are pushing for it though! This is where things get interesting, but it involves substantial effort.

Building a rule engine in c#

Rules can be built in run-time using configuration data stored in your database and evaluated. There are quite a few examples of this on the web. Check out the following implementations:. With Expression Trees, you can manipulate objects, properties, and methods at run-time. You can form dynamic, in-memory branches of code and execute them. Taking it a step further, you can load external assemblies via reflection into your application and write a web interface that allows you to construct rules around the objects contained in these assemblies.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I have a pretty decent list of the advantages of using a Rules Engine, as well as some reasons to use them, what I need is a list of the reasons why you should NOT use a Rules Engine.

Rules engines are not really intended to handle workflow or process executions nor are workflow engines or process management tools designed to do rules. I get very nervous when I see people using very large rule sets e. This often happens when the rules engine is a singleton sitting in the center of the enterprise in the hope that keeping rules DRY will make them accessible to many apps that require them.

I would defy anyone to tell me that a Rete rules engine with that many rules is well-understood. I'm not aware of any tools that can check to ensure that conflicts don't exist. I think partitioning rules sets to keep them small is a better option. Aspects can be a way to share a common rule set among many objects. I will give 2 examples from personal experience where using a Rules Engine was a bad idea, maybe that will help Lesson : Requirements tend to change a lot during initial release changes and do not warrant usage of rules.

Use rules when your business changes often not requirements. Eg:- A software that does your taxes will change every year as taxation laws change and usage of rules is an excellent idea. Release 1. Do not use rules as an alternative to code deploy. I'm a big fan of Business Rules Engines, since it can help you make your life much easier as a programmer. One of the first experiences I've had while working on a Data Warehouse project was to find Stored Procedures containing complicated CASE structures stretching over entire pages.

It was a nightmare to debug, since it was very difficult to understand the logic applied in such long CASE structures, and to determine if you have an overlapping between a rule at page 1 of the code and another from page 5. Overall, we had more than such rules embedded in the code. When we've received a new development requirement, for something called Accounting Destination, which was involving treating more than rules, i knew something had to change.

Back then I've been working on a prototype which later on become the parent of what now is a Custom Business Rule engine, capable of handling all SQL standard operators. Initially we've been using Excel as an authoring tool andlater on, we've created an ASP.

Now the system works fine, with very few bugs, and contains over rules for calculating this Accounting Destination.

I don't think such scenario would have been possible by just hard-coding. And the users are pretty happy that they can define their own rules without IT becoming their bottleneck. Overall, the biggest advantage of using a Business Rule Engines is that it allows the users to take back control over the Business Rule definitions and authoring, without the need of going to the IT department each time they need to modify something.

Building a Dynamic Business Rules Engine

It also the reduces the workload over IT development teams, which can now focus on building stuff with more added value. Another option is if you have a linear set of rules that only apply once in any order to get an outcome is to create a groovy interface and have developers write and deploy these new rules.

The advantage is that it is wickedly fast because normally you would pass the hibernate session OR jdbc session as well as any parameters so you have access to all your apps data but in an efficient manner. It's another way to avoid a rules engine and be able to be deployed dynamically yes, our groovy rules were deployed in a database and we had no recursion It is just another option They have to learn some groovy but that is very close to java so the learning curve is much better.

It really depends on your context. Rules engine have their place and the above is just another option if you have rules on a project that you may want to deploy dynamically for very simplified situations that don't require a rules engine.

If any of these four traits are missing, you still might find a rules engine works for you, but every time I've tried it with even 1 missing, I've run into trouble. That's certainly a good start.A rules engine is all about providing an alternative computational model.

Instead of the usual imperative model, which consists of commands in sequence with conditionals and loops, a rules engine is based on a Production Rule System. This is a set of production rules, each of which has a condition and an action - simplistically you can think of it as a bunch of if-then statements. The subtlety is that rules can be written in any order, the engine decides when to evaluate them using whatever order makes sense for it.

A good way of thinking of it is that the system runs through all the rules, picks the ones for which the condition is true, and then evaluates the corresponding actions. The nice thing about this is that many problems naturally fit this model:. A rules engine is a tool that makes it easier to program using this computational model.

It may be a complete development environment, or a framework that can work with a traditional platform. Most of what I've seen in recent years are tools that are designed to fit in with an existing platform.

how to build a rules engine

At one time there was the notion of building an entire system using a tool like this, but now people wisely tend to use rule engines just for the sections of a system. The production rule computational model is best suited for only a subset of computational problems, so rules engines are better embedded into larger systems.

You can build a simple rules engine yourself. All you need is to create a bunch of objects with conditions and actions, store them in a collection, and run through them to evaluate the conditions and execute the actions. But mostly when people refer to "rules engine" they mean a product built specifically to help you build and run a rules engine. More efficient execution engines help to quickly evaluate conditions on hundreds of rules using specialized algorithms such as the Rete algorithm.

An important property of rule engines is chaining - where the action part of one rule changes the state of the system in such a way that it alters the value of the condition part of other rules. Chaining sounds appealing, since it supports more complex behaviors, but can easily end up being very hard to reason about and debug.

I've run into a few cases where people have made use of rules engine products, and each time things don't seem to have worked out well disclaimer: I'm not a statistically valid sample.

Often the central pitch for a rules engine is that it will allow the business people to specify the rules themselves, so they can build the rules without involving programmers.

As so often, this can sound plausible but rarely works out in practice. Even so, there's still value in a BusinessReadableDSLand indeed this is an area where I do see value in this computational model.

But here too lie dragons. The biggest one is that while it can make sense to cast your eyes down a list of rules and see that each one makes sense, the interaction of rules can often be quite complex - particularly with chaining. So I often hear that it was easy to set up a rules system, but very hard to maintain it because nobody can understand this implicit program flow.

This is the dark side of leaving the imperative computational model. For all the faults of imperative code, it's relatively easy to understand how it works.

With a production rule system, it seems easy to get to a point where a simple change in one place causes lots unintended consequences, which rarely work out well. I haven't spent enough time with these systems to get a sense of what heuristics we should follow to keep this implicit behavior under control. All of these lead me to think that there's a lot to be said for avoiding rules engine products.

The basic idea of production rules is very simple. In order to keep the implicit behavior under control you also need to limit the number of rules by keeping the rules within a narrow context.

This would argue for a more domain specific approach to rules, where a team builds a limited rules engine that's only designed to work within that narrow context.So i made some changes to the rule engine project to make that possible.

I released a new version at codeplex and here you can see a test that uses that method calls. Super Clean and nice implementation! Thanks for all your good work and effort. Its highly appreciated and is an inspiration to me and many other people in the community. Great rule engine. Thanks for sharing. Sorry for repeat but some piece is missing from my question.

Is there possibility define rules for nested object properties like Address. City using dot notation? I am very sorry but that feature a dot notation for object. I appreciate your clean codes and clear explanation. I wonder if it can extend the rule engine to evaluate against a generic dictionary so that each evaluation returns a pre-defined scale as in the Likert scale in surveys for a property of type TValue to be evaluated against a list of K TKey? I have troubles to understand what you exactly need.

You want to evaluate a dictionary of type TKey, TValue. So each dictionary entry holds what, and which part should be evaluated against what rule? If you could clearify your question or give me a test with the call you would like to make, maybe i could help you.

Thank you for the quick responding. My question is how to extend the rule engine so that for each source or property of an object, a rating of integer value can be returned. For example, we can evaluate the value against a dictionary of such that if the temperature is less than 32, return 1, if temp is between So each property is rated based on a user-defined rule dictionary or a set of KeyValuePairs.

Does this make sense? I would implement it the following way but i am not sure if that is what you need. I changed some parts in the ruleengine and now you can do what you want to do.

So with the new Version 1. Here is the test that shows how it could work:. AreEqual result4, false ; Assert. AreEqual person3. CancelBenefits, true ; Assert. ReceiveBenefits, false ; Assert. StopBenefits, false. I want to replace SetAge 45 with SetAge x where x can be a function call or an expression e. I am very sorry but that functionality is not included in the rule engine.

I am thinking about implementing a rule engine 2. Just wanted to say thank you for the updates and taking suggestions to constantly improve. Love it. AreEqual person1. CancelBenefits, true. I am currently working on a complex data manipulation project that reads from CSV files into in-memory LINQ collections and then performs complex queries upon them to calculate price based on specific rules.Why Build a Business Rules Engine.

Data Modeling and Database Design. The Atomicity of Business Rules. The "Black Box" Problem. The Components of a Business Rules Engine. Populating Table Data in the Repository. Populating Column Data in the Repository. Populating Relationship and Subtype Data in the Repository.

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Populating Reference Data in the Repository. Defining Business Processes and Related Information. Extending the Database. Managing the Database. Implementing a Simple Business Rule. Rule Types for Checking Referential Integrity.

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Rules with Subtypes and Business Metadata. Debugging in Business Rules Engines. Managing the Business Rules Engine. Appendix A: Using the Sample Application. Covers user requirements, data modeling, metadata, and more.

how to build a rules engine

Malcolm Chisholm holds an M. His expertise has allowed him to work in various industries focusing on systems development and data administration. We are always looking for ways to improve customer experience on Elsevier. We would like to ask you for a moment of your time to fill in a short questionnaire, at the end of your visit. If you decide to participate, a new browser tab will open so you can complete the survey after you have completed your visit to this website.

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Rule Engine in Java using Generics - Tech Primers

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