Documentation: Exception handling added

Author: hANSIc99

DOKU.md

@@ -19,7 +19,7 @@
 
 The execution of elements is logged in a file that changes daily.
 The log files are archived under `~/Pythonic/log (Linux)` or `%HOMEPATH%\Pythonic\log` (Windows).
-Pythonic's web service provides an overview of available log files at **http://<address-info>:7000/log**.
+Pythonic's web service provides an overview of available log files at **http://\<address-info>:7000/log**. Single log files can be accessed witch the following scheme: **http://\<address-info>:7000/\<year>_\<month>_\<day>.txt**.
 
 - INFO
  - Ordinary debug trace messages
@@ -30,14 +30,18 @@ Pythonic's web service provides an overview of available log files at **http://<
  - Can be switched on or off by the user (checkbox in element configuration)
  - A log entry of this type is created when the element returns data of type PythonicError
  - Implementation in own code is optional
-- Critical (Unhandled exception):
- - Is signalized in the GUI an (,,Exception occured, open log for details)
- - Log entry (type ERROR) is made
+- ERROR (Unhandled exception):
+ - Caused by an unhandles exception
+ - Is signalized in the GUI ("Exception occured, open log for details")
  - Is always active (implementation not optional)
 
 ### Exception handling
 
-
+1. Elements should throw an exception when configuration data is missing or cannot be processed.
+2. Elements should try to handle all possible exceptions internally and only throw critical exceptions.
+3. The result of a operation (if successfull or not (see #2)) should always be forwarded to subsequent elements in order to react to a possible failed call. If the result of a failed call could be processed by an subsequent element, it should be wrapped in the `PythonicError` type.
+4. In case of a failed call, a meaningful message or the exception text should returned (`PythonicError` as data parameter in returned `Record` type)
+5. Don't to use `logging.error` or `logging.warning` as it has no effect if used in combination with multiprocessing.
 
 ## Elements