Process implementation is the application logic to handle requests. For example, the ThriftCLIService.ExecuteStatement() method implements the logic to compile and execute a Hive query.
Dependencies of HS2
The metastore can be configured as embedded (in the same process as HS2) or as a remote server (which is a Thrift-based service as well). HS2 talks to the metastore for the metadata required for query compilation.
HS2 clients: HiveServer2 Clients
User interface: Web UI for HiveServer2
Metrics: Hive Metrics
Cloudera blog on HS2: http://blog.cloudera.com/blog/2013/07/how-hiveserver2-brings-security-and-concurrency-to-apache-hive/