24.Unlike instance recovery, media
recovery must be initiated by the user. Media recovery
updates restored datafiles so the information in them
corresponds to the most recent time point before the disk
failure, including the committed data in memory that was
lost because of the failure.
(介质恢复由用户发起.介质恢复数据文件信息到相应的介质失败时最近的时间点,包括那些在内存中以提交的但丢失了的数据)
25.If the database’s redo log operates in NOARCHIVELOG mode, the database can be
completely recovered from instance failure but not from disk failure.
(如果数据库在不归档日志模式下，那么数据库只能恢复例程失效而不能恢复介质的失败)
26.Differences Between Data Warehouse and OLTP Systems(数据仓库与在线联机事务处理)
1)Workload(工作量)
OLTP systems support only predefined operations. Your applications might be
specifically tuned or designed to support only these operations.
(联机系统仅支持预先确定了操作)
2)Data Modifications
A data warehouse is updated on a regular basis by the ETL process (run nightly or
weekly) using bulk data modification techniques. The end users of a data
warehouse do not directly update the data warehouse.
(数据仓库数据的更新通过ETL进程依据有序的、规则的原理基础，最终用户不能直接更新数据仓库的数据)
In OLTP systems, end users routinely issue individual data modification statements
to the database. The OLTP database is always up to date, and reflects the current
state of each business transaction.
(联机系统最终用户经常执行个别的数据更新，它常常更新到最近的日期，它反映的是最近的业务状态)
3)Schema Design
Data warehouses often use denormalized or partially denormalized schemas (such
as a star schema) to optimize query performance.
(数据仓库经常使用非规格化或半规格化的用户方案达到高效的查询性能)
OLTP systems often use fully normalized schemas to optimize
(联机系统常常使用全规格化的用户方案达到)
4)Historical Data
Data warehouses usually store many months or years of data. This is to support
historical analysis.
OLTP systems usually store data from only a few weeks or months.
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