# UDT - Parameter Inheritance

**URL:** <https://forum.inductiveautomation.com/t/udt-parameter-inheritance/29609>\
**Category:** Ignition\
**Tags:** ignition80\
**Created:** [November 1, 2019, 8:04pm UTC](https://forum.inductiveautomation.com/t/udt-parameter-inheritance/29609 "2019-11-01T20:04:07Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![robwarren](https://avatars.discourse-cdn.com/v4/letter/r/7cd45c/32.png) [@robwarren](https://forum.inductiveautomation.com/u/robwarren)\
**Post date:** [November 1, 2019, 8:04pm UTC](https://forum.inductiveautomation.com/t/udt-parameter-inheritance/29609/1 "2019-11-01T20:04:07Z")

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Hello,  
This is a pretty basic question, but I’m worried that I’m going to do a poor job of explaining it.

For all of my tags, I have “Base UDT’s”.  
I have several complex UDT’s that use these Base UDT’s.

I have a couple of questions regarding how the parameters are inherited from the UDT’s in the tags:

First - If I use the Base UDT’s in my complex UDT, Like this:

Base UDT  
-Param1 ‘Base Historian’ = MYHISTORIAN

Complex UDT  
MY\_BASE\_UDT\_Tag

![image](https://us1.discourse-cdn.com/inductiveautomation/original/2X/3/32af98e4c60876eb4f685cf1a345b0cf86c91bb1.png)

now I create a tag:  
MY\_COMPLEX\_UDT\_Tag

The Param1 ‘Base Historian’ value will be “MYHISTORIAN”, correct?

 ![image](https://us1.discourse-cdn.com/inductiveautomation/original/2X/4/4c949eb40f3c9be41d12cf5ad79c97a0882a14bd.png)  
In answer to my own question, yes.

Second Question:  
If I then go into the Complex UDT/MY\_BASE\_UDT\_Tag and override Param1 ‘Base Historian’ to be a value of “DIFFERENTHISTORIAN”,  
Then I create a tag:  
DIFFHIST\_COMPLEX\_UDT\_Tag, the Param1 ‘Base Historian’ value will be “DIFFERENTHISTORIAN”.

![image](https://us1.discourse-cdn.com/inductiveautomation/original/2X/2/20c96e75da06cad86f1880a36d661dd47e709a3b.png)  
(Check.)

Finally, I go back into my Complex UDT/MY\_BASE\_UDT\_Tag and delete the value in Param1 ‘Base Historian’ in an attempt to “un-override” the parameter, should the parameter of my DIFFHIST\_COMPLEX\_UDT\_Tag/MY\_BASE\_UDT\_Tag Param1 ‘Base Historian’ now equal “MYHISTORIAN”?

![image](https://us1.discourse-cdn.com/inductiveautomation/original/2X/b/bacada078c6a1eea7d60fe8112b2fef703f15604.png)

Upon testing, the answer is no. I don’t understand why this is. Any suggestions?

When I create a new BASE\_UDT\_INSTANCE, the parameter updates when I change it on the UDT Data Type. I would expect these changes to also affect any complex UDT’s using that base UDT.

![image](https://us1.discourse-cdn.com/inductiveautomation/original/2X/e/e7b5a6deef0d471725e2909091f68d2884aa9597.png)

A quick test tells me that if you don’t ever override it in the complex UDT, then the base changes will “trickle down”.  
 ![image](https://us1.discourse-cdn.com/inductiveautomation/original/2X/c/c81756b80d3eefd07469b21770942cc7cd4cdb60.png)

 ![image](https://us1.discourse-cdn.com/inductiveautomation/original/2X/c/c960560ece12c1fad9990bce10d74e8454df5d79.png)

Can I “un-override” the parameter in the complex UDT?

This post evolved quite a bit as I was writing it and doing the testing / capturing screen shots.

Thanks,  
-Rob W.