问题的关键是一些应用要求这种访问是完全事务化的，并且数据完整性在不同数据源间也能得到保证。
The key is that some applications require that this access be fully transactional _- that data integrity be maintained across the data sources.
像SSIS这样的ETL工具就可以实现这些功能，如，在不同的系统间进行数据的移动、数据的再格式化、完整性校验、关键值查询、衍生跟踪等，SSIS也证明了它是一个有能力和有着多方面用途的ETL工具。
ETL tools like SSIS can perform these functions such as moving data between systems, reformatting data, integrity checking, key lookups, tracking lineage, and more.
数据集内的每个属性都应该是规格化的，因此，每个值均除以该属性在数据集内的最高值与最低值间的差值。
Every attribute in the data set should be normalized, whereby each value is divided by the difference between the high value and the low value in the data set for that attribute.
应用推荐