NWDI & ISA 5.0

I was told that in order to develop/modify the standard ISA 5.0 application, NWDI is mandatory. When modifying ISA 4.0, our team used a combination of NWDS and TextPad.

Can some one confirm or rebuke this? Also, if it is not mandatory, but it would make my life a lot easier, I'd like to know that too.

I'm not exactly sure what the NWDI provides a developer. Is it similar to Microsoft Visual Studio in some respects?

Any information is greatly appreciated.

Thanks,

Bryan