Hi @一江吴 

Basically, this Community doesn't answer questions regarding licensing, as this topic is too "hot" and often like rocket science. 

Therefore, always try to align with your sales rep, first. 

But I try to answer without guarantee being right: If you only have an App Engine license you also have a number of end users who are allowed to use your instance (as per your contract). And you are allowed to build custom applications and create custom tables (within the limitations). And in your case you also should create custom roles for your custom applications which then are assigned to the end users. And these roles are not allowed to include licensable roles from other modules like "itil". Instead, you completely have to rely on individual custom ACLs for your custom tables.

Maik