4.3. Rule expressions in FEEL
Friendly Enough Expression Language (FEEL) is an expression language defined by the Object Management Group (OMG) DMN specification. FEEL expressions define the logic of a decision in a DMN model. FEEL is designed to facilitate both decision modeling and execution by assigning semantics to the decision model constructs. FEEL expressions in decision requirements diagrams (DRDs) occupy table cells in boxed expressions for decision nodes and business knowledge models.
For more information about FEEL in DMN, see the OMG Decision Model and Notation specification.
4.3.1. Data types in FEEL
Friendly Enough Expression Language (FEEL) supports the following data types:
- Numbers
- Strings
- Boolean values
- Dates
- Time
- Date and time
- Days and time duration
- Years and months duration
- Functions
- Contexts
- Ranges (or intervals)
- Lists
The DMN specification currently does not provide an explicit way of declaring a variable as a function
, context
, range
, or list
, but Red Hat Decision Manager extends the DMN built-in types to support variables of these types.
The following list describes each data type:
- Numbers
Numbers in FEEL are based on the IEEE 754-2008 Decimal 128 format, with 34 digits of precision. Internally, numbers are represented in Java as
BigDecimals
withMathContext DECIMAL128
. FEEL supports only one number data type, so the same type is used to represent both integers and floating point numbers.FEEL numbers use a dot (
.
) as a decimal separator. FEEL does not support-INF
,+INF
, orNaN
. FEEL usesnull
to represent invalid numbers.Red Hat Decision Manager extends the DMN specification and supports additional number notations:
-
Scientific: You can use scientific notation with the suffix
e<exp>
orE<exp>
. For example,1.2e3
is the same as writing the expression1.2*10**3
, but is a literal instead of an expression. -
Hexadecimal: You can use hexadecimal numbers with the prefix
0x
. For example,0xff
is the same as the decimal number255
. Both uppercase and lowercase letters are supported. For example,0XFF
is the same as0xff
. -
Type suffixes: You can use the type suffixes
f
,F
,d
,D
,l
, andL
. These suffixes are ignored.
-
Scientific: You can use scientific notation with the suffix
- Strings
Strings in FEEL are any sequence of characters delimited by double quotation marks.
Example
"John Doe"
- Boolean values
-
FEEL uses three-valued boolean logic, so a boolean logic expression may have values
true
,false
, ornull
. - Dates
Date literals are not supported in FEEL, but you can use the built-in
date()
function to construct date values. Date strings in FEEL follow the format defined in the XML Schema Part 2: Datatypes document. The format is"YYYY-MM-DD"
whereYYYY
is the year with four digits,MM
is the number of the month with two digits, andDD
is the number of the day.Example:
date( "2017-06-23" )
Date objects have time equal to
"00:00:00"
, which is midnight. The dates are considered to be local, without a timezone.- Time
Time literals are not supported in FEEL, but you can use the built-in
time()
function to construct time values. Time strings in FEEL follow the format defined in the XML Schema Part 2: Datatypes document. The format is"hh:mm:ss[.uuu][(+-)hh:mm]"
wherehh
is the hour of the day (from00
to23
),mm
is the minutes in the hour, andss
is the number of seconds in the minute. Optionally, the string may define the number of milliseconds (uuu
) within the second and contain a positive (+
) or negative (-
) offset from UTC time to define its timezone. Instead of using an offset, you can use the letterz
to represent the UTC time, which is the same as an offset of-00:00
. If no offset is defined, the time is considered to be local.Examples:
time( "04:25:12" ) time( "14:10:00+02:00" ) time( "22:35:40.345-05:00" ) time( "15:00:30z" )
Time values that define an offset or a timezone cannot be compared to local times that do not define an offset or a timezone.
- Date and time
Date and time literals are not supported in FEEL, but you can use the built-in
date and time()
function to construct date and time values. Date and time strings in FEEL follow the format defined in the XML Schema Part 2: Datatypes document. The format is"<date>T<time>"
, where<date>
and<time>
follow the prescribed XML schema formatting, conjoined byT
.Examples:
date and time( "2017-10-22T23:59:00" ) date and time( "2017-06-13T14:10:00+02:00" ) date and time( "2017-02-05T22:35:40.345-05:00" ) date and time( "2017-06-13T15:00:30z" )
Date and time values that define an offset or a timezone cannot be compared to local date and time values that do not define an offset or a timezone.
重要If your implementation of the DMN specification does not support spaces in the XML schema, use the keyword
dateTime
as a synonym ofdate and time
.- Days and time duration
Days and time duration literals are not supported in FEEL, but you can use the built-in
duration()
function to construct days and time duration values. Days and time duration strings in FEEL follow the format defined in the XML Schema Part 2: Datatypes document, but are restricted to only days, hours, minutes and seconds. Months and years are not supported.Examples:
duration( "P1DT23H12M30S" ) duration( "P23D" ) duration( "PT12H" ) duration( "PT35M" )
重要If your implementation of the DMN specification does not support spaces in the XML schema, use the keyword
dayTimeDuration
as a synonym ofdays and time duration
.- Years and months duration
Years and months duration literals are not supported in FEEL, but you can use the built-in
duration()
function to construct days and time duration values. Years and months duration strings in FEEL follow the format defined in the XML Schema Part 2: Datatypes document, but are restricted to only years and months. Days, hours, minutes, or seconds are not supported.Examples:
duration( "P3Y5M" ) duration( "P2Y" ) duration( "P10M" ) duration( "P25M" )
重要If your implementation of the DMN specification does not support spaces in the XML schema, use the keyword
yearMonthDuration
as a synonym ofyears and months duration
.- Functions
FEEL has
function
literals (or anonymous functions) that you can use to create functions. The DMN specification currently does not provide an explicit way of declaring a variable as afunction
, but Red Hat Decision Manager extends the DMN built-in types to support variables of functions.Example:
function(a, b) a + b
In this example, the FEEL expression creates a function that adds the parameters
a
andb
and returns the result.- Contexts
FEEL has
context
literals that you can use to create contexts. Acontext
in FEEL is a list of key and value pairs, similar to maps in languages like Java. The DMN specification currently does not provide an explicit way of declaring a variable as acontext
, but Red Hat Decision Manager extends the DMN built-in types to support variables of contexts.Example:
{ x : 5, y : 3 }
In this example, the expression creates a context with two entries,
x
andy
, representing a coordinate in a chart.In DMN 1.2, another way to create contexts is to create an item definition that contains the list of keys as attributes, and then declare the variable as having that item definition type.
The Red Hat Decision Manager DMN API supports DMN
ItemDefinition
structural types in aDMNContext
represented in two ways:-
User-defined Java type: Must be a valid JavaBeans object defining properties and getters for each of the components in the DMN
ItemDefinition
. If necessary, you can also use the@FEELProperty
annotation for those getters representing a component name which would result in an invalid Java identifier. -
java.util.Map
interface: The map needs to define the appropriate entries, with the keys corresponding to the component name in the DMNItemDefinition
.
-
User-defined Java type: Must be a valid JavaBeans object defining properties and getters for each of the components in the DMN
- Ranges (or intervals)
FEEL has
range
literals that you can use to create ranges or intervals. Arange
in FEEL is a value that defines a lower and an upper bound, where either can be open or closed. The DMN specification currently does not provide an explicit way of declaring a variable as arange
, but Red Hat Decision Manager extends the DMN built-in types to support variables of ranges.The syntax of a range is defined in the following formats:
range := interval_start endpoint '..' endpoint interval_end interval_start := open_start | closed_start open_start := '(' | ']' closed_start := '[' interval_end := open_end | closed_end open_end := ')' | '[' closed_end := ']' endpoint := expression
The expression for the endpoint must return a comparable value, and the lower bound endpoint must be lower than the upper bound endpoint.
For example, the following literal expression defines an interval between
1
and10
, including the boundaries (a closed interval on both endpoints):[ 1 .. 10 ]
The following literal expression defines an interval between 1 hour and 12 hours, including the lower boundary (a closed interval), but excluding the upper boundary (an open interval):
[ duration("PT1H") .. duration("PT12H") )
You can use ranges in decision tables to test for ranges of values, or use ranges in simple literal expressions. For example, the following literal expression returns
true
if the value of a variablex
is between0
and100
:x in [ 1 .. 100 ]
- Lists
FEEL has
list
literals that you can use to create lists of items. Alist
in FEEL is represented by a comma-separated list of values enclosed in square brackets. The DMN specification currently does not provide an explicit way of declaring a variable as alist
, but Red Hat Decision Manager extends the DMN built-in types to support variables of lists.Example:
[ 2, 3, 4, 5 ]
All lists in FEEL contain elements of the same type and are immutable. Elements in a list can be accessed by index, where the first element is
1
. Negative indexes can access elements starting from the end of the list so that-1
is the last element.For example, the following expression returns the second element of a list
x
:x[2]
The following expression returns the second-to-last element of a list
x
:x[-2]
Elements in a list can also be counted by the function
count
, which uses the list of elements as the parameter.For example, the following expression returns
4
:count([ 2, 3, 4, 5 ])