oeCloud Business Rules Engine

Introduction:

As name suggests oeCloud business rule engine is a framework to write pre-defined and custom rules for business validations and decision making. oeCloud business rule engine is developed based on DMN (Decision Model and Notation v 1.1) specification and use FEEL (Friendly Enough Expression Language) to write expressions for rules.

What is DMN:

One of the ways to express decision logic is decision table. A decision table is a tabular representation of a set of related input and output expressions, organized into rules indicating which output entry applies to a specific set of input entries. The decision table contains all (and only) the inputs required to determine the output. Moreover, a complete table contains all possible combinations of input values (all the rules). Decision table is part of DRG (Decision Requirement Graph)

A decision table consists of:

• An information item name: the name of an Information Item, if any, for which the decision table is its value expression. This will usually be the name of the Decision or Business Knowledge Model for which the decision table provides the decision logic.
• An output label, which can be any text to describe the output of the decision table. The result of a decision table must be referenced using the information item name, not the output label, in another expression.
• A set of inputs (zero or more). Each input is made of an input expression and a number of input entries. The specification of input expression and all input entries is referred to as the input clause.
• A set of outputs (one or more). A single output has no name, only a value. Two or more outputs are called output components. Each output component SHALL be named. Each output (component) SHALL specify an output entry for each rule. The specification of output component name (if multiple outputs) and all output entries is referred to as an output clause.
• A list of rules (one or more) in rows or columns of the table (depending on orientation), where each rule is composed of the specific input entries and output entries of the table row (or column). If the rules are expressed as rows, the columns are clauses, and vice versa. [Figure: Decision Table example (horizontal orientation: rules as rows)]

[Figure: Decision Table example (horizontal orientation: multiple output)]

DMN input would be given by user in excel file. Here is an example of excel (.xlsx) file content

Below is the programmatic representation of above input

What is FEEL:

FEEL stands for Friendly Enough Expression Language and it has the following features:

• Side-effect free
• Simple data model with numbers, dates, strings, lists, and contexts
• Simple syntax designed for a wide audience
• Three-valued logic (true, false, null) based on SQL and PMML

We define a graphical notation for decision logic called boxed expressions. This notation serves to decompose the decision logic model into small pieces that can be associated with DRG artifacts. The DRG plus the boxed expressions form a complete, mostly graphical language that completely specifies Decision Models. A boxed expression is either:

• a decision table
• a boxed FEEL expression
• a boxed invocation
• a boxed context
• a boxed list
• a relation, or
• a boxed function

Example of FEEL expression in oeCloud Business Rule Engine shown in previous excel content. Each cell contains an expression written in FEEL.

For more information on FEEL please refer js-feel.

Invoking rule from javascript code

Following code snippet gives sample code for executing a decision table with name “abc” with payload “{x:1}”

var DecisionTable = loopback.findModel('DecisionTable');
var payload = { x: 1};
DecisionTable.exec('abc', payload, options, function(err, data) {
  if (err) {
     throw(err);
  }
  console.log(data);
}

Remote execution of rule

POST on /api/decisiontables/exec/:name endpoint will do

• Find the decision table excel with name given in url
• Use the body of the request payload as input to the decision table execution
• return the output from the execution back to the caller

Sample rules

validation.xlsx

PostBureauRiskCategory.xlsx

ElectricityBill.xlsx

NOTE :

For guide please refer Business Rule Engine.

For comprehensive set of documentation on DMN, you can refer to 1.1 specification given in below url:

DMN 1.1