（1）This catalog is another Oracle database with special RMAN catalog tables that store metadata about backups, much the same way that the data dictionary stores data about objects in the database.
这里说得catalog tables是指什么啊？
catalog 具体是指什么啊？ 是从表空间中划分存放backup相关信息的存储空间么？因为在创建的时候需要指出使用的是哪个表空间：
create catalog tablespace data;
（2）The RMAN utility enables you to use a target database without utilizing the recovery catalog database. The target database is the database targeted by RMAN for backup or recovery actions. Because most of the recovery catalog information is stored in the target database’s control file, RMAN supports the ability to use just the control file to perform backup and recovery operations.
如果不使用catalog的话，rman是直接使用control file去存放backup相关信息的么？那如果我创建了catalog是不是默认为使用它？这些信息具体是指什么呢？
