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Telelogic System Architect (steve huntington)
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Topic Title: Incorrect "Allow Null" column settings
Topic Summary: Incorrect "Allow Null" column settings in UDT
Created On: 29-Aug-2008 17:27
Status: Read Only
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 29-Aug-2008 17:27
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Arif Hussain

Posts: 53
Joined: 22-Dec-2005

In the Physical Data Model, my users have defined UDTs (User Data type definitions) to specify (column) types.

Each UDT can apply to lots of columns, some of which can be null and others which will cannot be null.

The "Allow Null" choice is set in the UDT definition and enforced for all associated columns.
My users say that this is totally wrong and that the "Allow Null" should be on the column only and not on the UDT.

Anyone in the same situation?
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 9-Sep-2008 13:44
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Peter Crabb-Wyke

Posts: 73
Joined: 3-May-2007

I hadn't even noticed that these now existed.

Looking at the documentation a UDT appears to be a mapping of a domain onto a specific database. The value would be to enable a non standard mapping from logical to physical where there were contstraints imposed by legacy or third party applications.

Its a very trivial looking addition but, if I was back in data modelling, it could totally change my approach to how we used domains with data elements.

There are many arguements over the advisability of using nulls at all but as the domain definition does not consider nullity it seems inappropriate to suddenly manage it in a UDT.

<edit>
Thinking about this a bit more I think that the designer may have intended a different approach to domains to the one that is often used. Rather than generically identifying things like dates, monetary amounts etc I would think that something more granular was assumed. For example separate "Sell Price" and "Purchase Price" domains. At that level I suspect that the issue would largely go away but I imagine that your client is treating these as classic domain formats.
</edit>
<edit>
Just tested it. The whole thing looks very messy. If your target database has a non standard definition for a domain you can change it after the PDM gen but if you predefine the variant then it will reset to the original domain value. I assume that creating an updated PDM will reset any non-standard UDTs which rather defeats the object of the defintion type in my view.
<edit>

Edited: 9-Sep-2008 at 14:25 by Peter Crabb-Wyke
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