Which is the base table of the configuration management database hierarchy?

The `cmdb_ci` table is the base table for all Configuration Items, but it itself extends from the more fundamental `cmdb` table, meaning it is not the absolute base of the entire hierarchy.

The `cmdb` table is the most abstract, top-level base table in ServiceNow's CMDB hierarchy. All other CMDB classes and Configuration Items (CIs), including `cmdb_ci`, ultimately extend from this fundamental table.

The `cmdb_rel_ci` table stores relationships between Configuration Items, which is an important part of the CMDB, but it is not the base table for the CI hierarchy itself.

`ucmdb` is not a standard ServiceNow table name for the CMDB hierarchy's base; it might refer to a different CMDB product or a custom table.