Defines service registry contracts application are likely to want to utilize for configuring Hibernate behavior. Service registries are designed to be hierarchical. This works in 2 fashions. First registries can "hide" or "override" services from parent registries. It also allows granular building of registries as services become available. org.hibernate.boot.registry.BootstrapServiceRegistry is the base service registry, intended to be built via org.hibernate.boot.registry.BootstrapServiceRegistryBuilder if you need customization. For non-customized org.hibernate.boot.registry.BootstrapServiceRegistry usage, the org.hibernate.boot.registry.BootstrapServiceRegistryBuilder and org.hibernate.boot.registry.BootstrapServiceRegistry can be bypassed altogether. Usually the next level in a standard registry set up is the org.hibernate.boot.registry.StandardServiceRegistry, intended to be built by the org.hibernate.boot.registry.StandardServiceRegistryBuilder if you need customization. The builder optionally takes the org.hibernate.boot.registry.BootstrapServiceRegistry to use as a base; if none is provided a default one is generated assuming sensible defaults in Java SE and EE environments, particularly in respect to Class loading.