[Pig Wiki] Update of "PigDeveloperCookbook" by SanthoshSrinivasan

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The following page has been changed by SanthoshSrinivasan:
http://wiki.apache.org/pig/PigDeveloperCookbook

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   * For `User Errors`, throw `ParseException` that contains meaningful message. For batch and interactive processing, catch the exception in Grunt and log the exception message to stderr. The same can be done with the developer in the embedded case. In debug mode, log the exception stack into the client side log.
   * For `Internal Errors`, throw `!RuntimeException` or its derivation. Catch the exception in main, log it, including the stack, to the client side log. Write failure message to stderr pointing to the log file.
-  * For `Frontend Errors`, throw newly created `FrontendException` that is a subclass of RuntimeException. Catch the exception in main, log it, including the stack, to the client side log. Write failure message to stderr pointing to the log file. In the future, we might find it useful to further subdivide this errors in which case we might subclass the `FrontendException` class. 
+  * For `Frontend Errors`, throw `FrontendException` or a subclass of `FrontendException`. Catch the exception in main, log it, including the stack, to the client side log. Write failure message to stderr pointing to the log file. The front-end consists of multiple components - parser, type checker, optimizer, translators, etc. All the errors from these components can be categorized as front-end errors. Components that are part of the front end will throw specific exceptions that capture the context. For example, the parser throws a `ParseException`, the type checker will throw a `TypeCheckerException`, etc. A list of the exceptions thrown in the front-end are as follows.
+ 
+    1. `FrontendException` Generic front-end exception (subclass of `PigException`)
+    1. `JobCreationException` Used for indicating errors during Map Reduce job creation (subclass of `FrontendException`)
+    1. `LogicalToPhysicalTranslatorException` Used for indicating errors during logical plan to physical plan translation (subclass of `VisitorException`)
+    1. `MRCompilerException` Used for indicating errors during map reduce plan compilation from physical plan (subclass of `VisitorException`)
+    1. `OptimizerException` Used for indicating errors during logical plan optimization (subclass of `FrontendException`)
+    1. `PigException` Generic exception in Pig (subclass of `IOException` and the superclass of all exceptions in Pig)
+    1. `PlanException` Used for indicating errors during plan/graph operations (subclass of `FrontendException`)
+    1. `PlanValidationException` Used for indicating errors during plan validation (subclass of `VisitorException`)
+    1. `SchemaMergeException` Used for indicating errors during schema merges (subclass of `FrontendException`)
+    1. `TypeCheckerException` Used for indicating errors due to type checking (subclass of `VisitorException`)
+    1. `VisitorException` Generic exception used for indicating errors when visiting a plan (subclass of `FrontendException`)
+ 
+  
   * For `Backend Errors` there will need to be backend specific way to get the error from the backend to the frontend. Once this is done, log the error into client side log file and throw `ExecuteException`. Catch the exception in main, log it, including the stack, to the client side log. Write failure message to stderr pointing to the log file.
   
  == Pig and Eclipse ==