js-feel

About

FEEL is an expression language based on DMN specification conformance level 3. Written using PEG.js - JavaScript Parser Generator. FEEL is a very powerful language built with the purpose of defining rules in Business Rule Engines. FEEL also offers an API to implement and execute Decision Table defined in excel (.xlsx)

Getting Started

FEEL is a completely flexible library which can be used with any project to add support for Decision Table. It also comes with a powerful expression language termed FEEL built-in to define a multitude of decision rules.

Installation

Development

# npm install
npm install js-feel --save

Contribution

# clone repo
git clone https://github.com/EdgeVerve/feel.git

# or fork repo

# install dependencies
npm install

# run test cases
npm test

# watch for changes in source and grammar
gulp watch

# generate parser from grammar
gulp generate

# lint source files
npm run lint

# lint-fix source files
npm run lintfix

Usage

Using Decision Table

Decision tables are defined in excel (.xlsx). Please check Sample Rules. Each cell in the body of the decision table has to be a valid FEEL expression. The following make use of FEEL parser to parse and execute expressions and hence the decision logic.

Excel to Decision Table

const { decisionTable } = require('feel')();

const csv = decisionTable.xls_to_csv('./test/StudentFinancialPackageEligibility.xlsx');
const decision_table = decisionTable.csv_to_decision_table(csv[0]);

Execute Decision Table

The Decision Table (decision_table) created in the previous step can be executed using; decisionTable.execute_decision_table

const payload = {"Student GPA" : 3.6,"Student Extra-Curricular Activities Count" : 4,"Student National Honor Society Membership" : "Yes"};
decisionTable.execute_decision_table("StudentFinancialPackageEligibility", decision_table,payload, (results)=> {
    console.log(results)
});

Using FEEL Standalone

const {feel} = require('feel')();

const rule = 'a + b - c';
const context = {
    a: 10,
    b: 20,
    c: 5
};

const parsedGrammar = feel.parse(rule);
parsedGrammar.build(context).then(result => {
    console.log(result);
}).catch(err => console.error(err));

Sample FEEL Expressions

Some valid FEEL expressions (logically categorized):

Arithmetic

• a + b - c
• ((a + b)/c - (d + e*2))**f
• 1-(1+rate/12)**-term
• (a + b)**-c
• date("2012-12-25") + date("2012-12-24")
• time("T13:10:06") - time("T13:10:05")
• date and time("2012-12-24T23:59:00") + duration("P1Y")

Comparision

• 5 in (<= 5)
• 5 in ((5..10])
• 5 in ([5..10])
• 5 in (4,5,6)
• 5 in (<5,>5)
• (a + 5) >= (7 + g)
• (a+b) between (c + d) and (e - f)
• date("2012-12-25") > date("2012-12-24")
• date and time("2012-12-24T23:59:00") < date and time("2012-12-25T00:00:00")

Conjunction

• a or b
• a and b
• ((a or b) and (b or c)) or (a and d)
• ((a > b) and (a > c)) and (b > c)
• ((a + b) > (c - d)) and (a > b)
• a or b or a > b
• (x(i, j) = y) and (a > b)
• (a + b) > (c - d) and (a > b)

For

• for a in [1,2,3] return a * a
• for age in [18..40], name in ["george", "mike", "bob"] return status

Function Definition

• function(age) age < 21
• function(rate, term, amount) (amount*rate/12)/(1-(1+rate/12)**-term)

If

• if applicant.maritalStatus in ("M", "S") then "valid" else "not valid"
• if Pre-Bureau Risk Category = "DECLINE" or Installment Affordable = false or Age < 18 or Monthly Income < 100 then "INELIGIBLE" else "ELIGIBLE"
• if "Pre-Bureau Risk Category" = "DECLINE" or "Installment Affordable" = false or Age < 18 or "Monthly Income" < 100 then "INELIGIBLE" else "ELIGIBLE"

Quantified

• some ch in credit history satisfies ch.event = "bankruptcy"

Date Time Semantics

• time("13:10:05@Etc/UTC").hour
• time("13:10:05@Etc/UTC").minute
• time("13:01:05+05:30").second
• date and time("2012-12-24T23:59:00").year
• date("2017-06-10").month
• date("2017-06-10").day
• duration("P13M").years
• duration("P1Y11M").months
• duration("P5DT12H10M").days
• duration("P5DT12H10M").hours
• duration("P5DT12H10M").minutes
• duration("P5DT12H10M25S").seconds

Date Time Conversion and Equality

• date("2012-12-25") – date("2012-12-24") = duration("P1D")
• date and time("2012-12-24T23:59:00") + duration("PT1M") = date and time("2012-12-25T00:00:00")
• time("23:59:00z") + duration("PT2M") = time("00:01:00@Etc/UTC")
• date and time("2012-12-24T23:59:00") - date and time("2012-12-22T03:45:00") = duration("P2DT20H14M")
• duration("P2Y2M") = duration("P26M")

Please note: This is not a complete list of FEEL Expressions. Please refer DMN Specification Document for detailed documentation on FEEL grammar.

Sample Rules

Validation.xlsx

PostBureauRiskCategory.xlsx

ElectricityBill.xlsx

Reference

For comprehensive set of documentation on DMN, you can refer to :

DMN Specification Document