Language Model

The Siddhi Language consists of following constructs.

1. Event Definitions
2. Queries
   
   1. Filters
   2. Windows
   3. Joins
   4. Patterns
   5. Sequences
3. Calls to external functions (not supported in 1.0)

Following provides an abstract BNF based definition for Siddhi language.

<query> ::= <define-stream> | <execution-query>

<define-stream> ::= define stream <stream-name> <attribute-name> <type> {<attribute-name> <type>}

<execution-query>::= <input> <output> [<projection>]

<input> ::= from <streams>

<output> ::= ((insert [<output-type>] into <stream-name>) | (return [<output-type>]))

<streams> ::= <stream>[#<window>] 

   |   <stream>#<window> [unidirectional] <join> [unidirectional] <stream>#<window> on <condition> within <time>

   |   [every] <stream> -> <stream> ... <stream> within <time>

   |  <stream>, <stream>, <stream> within <time>

<stream> ::= <stream-name> <condition-list>

<projection> ::= (<external-call> <attributelist>) | <attributelist> [group by <attribute-name> ][having <condition>]

<external-call> ::= call <name> ( <param-list> )

<condition-list> ::= {‘[’<condition>’]’}

<attributelist>::=(<attribute-name> [as <reference-name>]) | ( <function>(<param-list>) as <reference-name>)

<output-type> ::= expired-events | current-events | all-events

<param-list> ::= {<expression>}

<condition> ::= ( <condition> (and|or) <condition> ) | (not <condition>) | ( <expression> (==|!=|>=|<=|>|<|contains|instanceof) <expression> )

<expression> ::= ( <expression> (+ | - | / | * | %) <expression> ) | <attribute-name> | <int> | <long> | <double> | <float> | <string> | <time>

<time> ::= [<int>( years | year )]  [<int>( months | month )] [<int>( weeks | week )] [<int>( days | day )] [<int>( hours | hour )] [<int>( minutes | min | minute )] [<int>( seconds | second | sec )]

  [<int>( milliseconds | millisecond )]