previously
单词辨析：
指从现在起往前推算一段时间，通常和一般过去时的动词连用。
He left a moment ago.
他刚走。
There was a pond here three years ago.
3年前，这里有一个池塘。
指过去某时间之前的时间或泛指以前，通常与动词的现在完成时连用，有时也可与动词的过去完成时或一般过去时连用，也可用于具体的一段时间；在间接引语中用 before 而不用 ago。
Have you heard about it before?
你过去听说过这件事吗？
I have never met him before.
我以前从未见过他。
He said that he had met the man somewhere before.
他说他以前在什么地方见过这个人。
He was in Italy the week before.
他前一个星期在意大利。
泛指以前，有时常用于对比。
Formerly, Ted often lingered around a park, with nothing to do.
从前，特德时常在公园里闲逛，无所事事。
He was formerly a worker, but now he is a manager of a shop.
他曾经是个工人，可现在他是一家商店的经理。
与 before 用法相同，但更加正式。
I haven't met him previously.
我以前没有见过他。
She previously worked as a teacher.
她过去当过教师。
Six months previously he had quitted his job.
6个月前他辞职了。
相关例句：
Previously, we said that all of the data in the system is stored in a tree.
前面我们说系统中的所有数据都存储在一个树中。
Guyana's railways were previously owned by private companies
圭亚那的铁路以前是归私有企业所有的。
Previously she had very little time to work in her own garden.
以前，她没什么时间打理自己的花园。
Previously this was an informational file that you could query.
以前，数据库历史文件是一种信息文件，您可以对其进行查询。
She had rented the flat from the council some fourteen months previously.
大约14个月以前，她从地方政府那里租下了这套公寓。
This means that we have to set all the previously mentioned properties.
这意味着我们必须设置所有以前提到过的属性。