> ## Documentation Index
> Fetch the complete documentation index at: https://docs.aseeflow.org/llms.txt
> Use this file to discover all available pages before exploring further.

# FEEL Language Elements

<Info>
  **Heads Up!**

  This page provides information on the legacy FEEL Engine, that was used before the
  current [Scala-based FEEL Engine](/user-guide/dmn-engine/feel)
  was integrated into ASEE Flow.
</Info>

The ASEE Flow DMN engine supports FEEL for [input entries]. The FEEL term for
expression in input entries are simple unary tests. These simple unary tests
test an input value against an expression and return either `true` if the test
is satisfied or `false` otherwise. The expression can contain different
elements which are described in this sections.

## Comparison

FEEL simple unary tests support the following comparison operators. Please
note that the equals operator is empty and *not* `=`. Also, a non equal operator such as `!=`
does *not* exist. To express this, [negation] has to be used.

<table class="table table-striped">
  <tr> <th>Name</th> <th>Operator</th> <th>Example</th> <th>Description</th> </tr>
  <tr> <td>Equal</td> <td><code /></td> <td><code>"Steak"</code></td> <td>Test that the input value is equal to the given value.</td> </tr>
  <tr> <td>Less</td> <td><code>\<</code></td> <td><code>\< 10</code></td> <td>Test that the input value is less than the given value.</td> </tr>
  <tr> <td>Less or Equal</td> <td><code>\<=</code></td> <td><code>\<= 10</code></td> <td>Test that the input value is less than or equal to the given value.</td> </tr>
  <tr> <td>Greater</td> <td><code>></code></td> <td><code>> 10</code></td> <td>Test that the input value is greater than the given value.</td> </tr>
  <tr> <td>Greater or Equal</td> <td><code>>=</code></td> <td><code>>= 10</code></td> <td>Test that the input value is greater than or equal to the given value.</td> </tr>
</table>

## Range

Some [FEEL data types], such as numeric types and date types, can be tested against
a range of values. These ranges consist of a start value and an end value. The
range specifies if the start and end value is included in the range.

<table class="table table-striped">
  <tr> <th>Start</th> <th>End</th> <th>Example</th> <th>Description</th> </tr>
  <tr> <td>include</td> <td>include</td> <td><code>\[1..10]</code></td> <td> Test that the input value is greater than or equal to the start value and less than or equal to the end value. </td> </tr>
  <tr> <td>exclude</td> <td>include</td> <td><code>]1..10]</code> or <code>(1..10]</code></td> <td> Test that the input value is greater than the start value and less than or equal to the end value. </td> </tr>
  <tr> <td>include</td> <td>exclude</td> <td><code>\[1..10\[</code> or <code>\[1..10)</code></td> <td> Test that the input value is greater than or equal to the start value and less than the end value. </td> </tr>
  <tr> <td>exclude</td> <td>exclude</td> <td><code>]1..10\[</code> or <code>(1..10)</code></td> <td> Test that the input value is greater than the start value and less than the end value. </td> </tr>
</table>

## Disjunction

A FEEL simple unary test can be specified as conjunction of expressions. These
expressions have to either have [comparisons] or [ranges]. The test is `true` if
at least one of conjunct expressions is `true`.

Examples:

* `3,5,7`: Test if the input is either 3, 5 or 7
* `<2,>10`: Test if the input is either less than 2 or greater than 10
* `10,[20..30]`: Test if the input is either 10 or between 20 and 30
* `"Spareribs","Steak","Stew"`: Test if the input is either the String
  Spareribs, Steak or Stew
* `date and time("2015-11-30T12:00:00"),date and time("2015-12-01T12:00:00")`:
  Test if the input is either the date November 30th, 2015 at 12:00:00 o'clock or
  December 1st, 2015 at 12:00:00 o'clock
* `>customer.age,>21`: Test if the input is either greater than the `age`
  property of the variable `customer` or greater than 21

## Negation

A FEEL simple unary test can be negated with the `not` function. This means if
the containing expression returns `true`, the test will return `false`. Please
*note* that only one negation as first operator is allowed but it can contain
a [disjunction].

Examples:

* `not("Steak")`: Test if the input is not the String Steak
* `not(>10)`: Test if the input is not greater than 10, which means it is less
  than or equal to 10
* `not(3,5,7)`: Test if the input is neither 3, 5 nor 7
* `not([20..30])`: Test if the input is not between 20 and 30

## Qualified Names

FEEL simple unary tests can access variables and object properties by
qualified names.

Examples:

* `x`: Test if the input is equal to the variable `x`
* `>= x`: Test if the input is greater than or equal to the variable `x`
* `< customer.age`: Test if the input is less than the `age` property of the
  variable `customer`

## Date Functions

FEEL simple unary tests provide functions to create [date types]. The ASEE Flow
DMN engine supports the following date functions:

* `date and time("...")`: Creates a date and time value from a String with the
  format `yyyy-MM-dd'T'HH:mm:ss`

Examples:

* `date and time("2015-11-30T12:00:00")`: Test if the input is the date
  November 30th, 2015 at 12:00:00 o'clock
* `[date and time("2015-11-30T12:00:00")..date and
  time("2015-12-01T12:00:00")]`: Test if the input is between the date
  November 30th, 2015 at 12:00:00 o'clock and December 1st, 2015 at 12:00:00
  o'clock

[comparisons]: #comparison

[ranges]: #range

[disjunction]: #disjunction

[negation]: #negation

[FEEL data types]: /reference/dmn/feel/legacy/data-types

[date types]: /reference/dmn/feel/legacy/data-types#date

[input entries]: /reference/dmn/decision-table/rule#input-entry-condition