# Keywords

A rule is the most important construct in the grammar of openVALIDATION. It consists of a condition and an action. With a validation rule, the action is always an error message. The easiest way to express such a rule is a

**IF / THEN**construct.Keyword | Description |

`IF` | Selects the beginning of a rule and the next condition |

`THEN` | Marks the beginning of an error message |

`AND` | Selects the start of a new linked AND condition |

`OR` | Selects the start of a new linked OR condition |

Keyword | Description |

`MUST, SHOULD, HAVE, HAS` | An indicator identifies an expression as a rule. The condition in such a MUST expression contains an Implicit Negation! |

`MUST NOT, MUSTN'T, SHOULD NOT, SHOULDN'T, HAS NOT, HASN'T, HAVE NOT, HAVEN'T` | An indicator identifies an expression, as a rule |

Relational operations always has a left and a right operand and the corresponding comparison operator.

Keyword | Description |

`IS, EQUAL, EQUALS` | A relational operator '=' for numeric and string operands |

`ISN'T, IS NOT, NOT EQUAL, NOT EQUALS, NOT` | A relational operator '!=' for numeric and string operands |

`LESS, SMALLER, LOWER, FEWER, SHORTER` | A relational operator '<' for numeric operands |

`GREATER, BIGGER, LARGER, MORE, EXCEED, EXCEEDS, HIGHER` | A relational operator '>' for numeric operands |

`GREATER OR EQUAL, GREATER OR EQUALS, LEAST, AT LEAST` | A relational operator '>=' for numeric operands |

`LESS OR EQUAL, LESS OR EQUALS, MOST` | A relational operator '<=' for numeric operands |

`EXIST, EXISTS, GIVEN` | A relational operator for non-"null" |

`DOESN'T EXIST, DON'T EXIST, NOT EXIST` | A relational operator for null |

Keyword | Description |

`+, PLUS` | A mathematical operation for a simple addition |

`-, MINUS` | A mathematical operation for a simple subtraction |

`*, TIMES` | A mathematical operation for a simple multiplication |

`/, DIVIDED BY` | A mathematical operation for a simple division |

`MOD, MODULO` | A mathematical operation for a simple modulo calculation |

You can write comments in the rulebook. These do not contain any logic.

Keyword | Description |

`COMMENT` | A comment |

Keyword | Description |

`ERRORCODE, WITH ERRORCODE, WITH CODE, WITH ERROR` | Error messages often contain their own error codes for unique identification. |

Last modified 3yr ago