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
Decision Table
UsingDecision 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 = ; const csv = decisionTable;const decision_table = decisionTable;
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" : 36"Student Extra-Curricular Activities Count" : 4"Student National Honor Society Membership" : "Yes";decisionTable;
FEEL Standalone
Usingconst feel = ; const rule = 'a + b - c';const context = a: 10 b: 20 c: 5; const parsedGrammar = feel;parsedGrammar;
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
Reference
For comprehensive set of documentation on DMN, you can refer to :