Design:

1. phase 1 : the design goal here is to limit class-loading and access to environmental resources which might not yet be available (datasources, jndi,etc)
   1. build BootstrapServiceRegistry - this step is sort of optional and only really needed if user wants to:
      • override how class-loading works
      • supply explicit "provided" Integrator instances
      • override how "strategy selection" works (although can also be done via Java ServiceLoader resolution).
   2. build MetadataSources - this collects the sources of mapping information (HBM files, annotated classes, etc).
2. phase 2 : at this stage we assume the limits imposed on phase 1 are no longer applicable
   1. build StandardServiceRegistry
   2. build Metadata
   3. use StandardServiceRegistry and Metadata to build SessionFactory

The problem with this is that, from a user PoV, this sure seems like a lot of steps (is that just me?):

// phase 1
BootstrapServiceRegistry bootRegistry = new BootstrapServiceRegistryBuilder()...build();
MetadataSources metadataSources = new MetadataSources( bootRegistry )...;

// phase 2
StandardServiceRegistry standardRegistry = new StandardServiceRegistryBuilder( bootRegistry )...build();
Metadata metadata = metadataSources.getMetadataBuilder()...buildMetadata( standardRegistry );
SessionFactory sessionFactory = metadata.getSessionFactoryBuilder()...build();