In some cases, it is more practical to use an indirect reference between itemtypes by utilizing a string attribute, which stores code/uid/etc. This approach is especially useful in situations where regular relation between itemtypes are not possible or efficient.
Patching Framework is a Hybris OOTB framework, which is designed to simplify releasing of new code on production (for example automation of impex execution after new code deployment). Hybris provides a set of interfaces and abstract classes, which allows to write “Patches”, where Patch itself is a Java class that is executed during a system initialization or an update.
During migration on newer version of hybris you could find that Backoffice is not working due to failed context initialization with error in creating 'backofficeWarmUpTypeFacadeCaches' bean. Root cause of that issue is broken itemtype definition in composedtypes table.