The schema diagram is not exhaustive, however it maps the main entities. Foreign key constraints are NOT allowed because the sync process cannot guarantee the order in which entities arrive.
The database is contained in lib-database and is built using Door and Room. If you are familiar with Room database on Android, it should be straightforward. Door essentially extends Room to work on JVM and Javascript using Kotlin Multiplatform.
All entities and DAOs can be found in UmAppDatabase.kt.