Why a custom attribute created on parent CMDB table, creates the attribute on all its Child tables?

[Suggy]

When a custom field created on parent CMDB table, it creates the same custom field on all child tables.

Ex: I create a field 'u_test' on cmdb_ci_server, it then created this field explicitly on all its child tables (like on windows, linux, solaris tables etc) . You can see several entries in dictionary.

This is not the case with Task table. ie if I create a field on Task table, its stays there, but I can can reuse that field in its child tables.

Any reason behind this?

[Suggy]

@SteveMacWWT  My question is understood by @Slava Savitsky  and I got the answer that I am looking for..

[Slava Savitsky · Accepted solution]

In short, there are three kinds of table extension models in ServiceNow:

• Table per class
• Table per hierarchy
• Table per partition

Task and Configuration Item table hierarchies use different extension models. Hence the differences you see on the dictionary level. For more information about table extension models, refer to this article from the product documentation.

[Suggy]

Thank you @Slava Savitsky