Thank's for your reply.

I have a another question. does java could be a script and then pass data into rex ?

Arbitrary script means that it can be a shell script (on Windows this would be a batch file), a Python script or a script in any other language (e.g. PHP).

If you are referring to this general description of REX on the Raspberry Pi then it means that you can e.g. read some sensor value using e.g. a Python script and then pass the value to the control algorithm. Or you can have some control algorithm in REX and pass its output to a script which will execute the necessary actions.

To be more specific, you can e.g. have a Python script which will read text messages from a GSM modem, parse them and pass the numeric values into the control algorithm. This allows you to define e.g. the desired temperature in your house via a text message.

Could you tell me what is "Arbitrary script executable on the Raspberry Pi" ?