Common Data Model is a standard of schemas, you are free to use it (the repository with the schema is at the following address https://github.com/microsoft/CDM) but if you don't use an implementation (like the Power Platform or another software that supports the CDM) you need to create your own.
Let's say you have your SQL engine (MySQL for example) and there you create the exact schema defined for the account, is compatible with CDM? yes
hope it helps
