As part of this exercise, you will also learn about the EntityManager API for storing and retrieving data, rather than the simple map APIs.

作为本练习的一部分，您还将学习使用EntityManager API存储和检索数据，而不是使用简单的map API。

youdao

Directory operations include storing new data in a directory, searching for and retrieving stored data, deleting unwanted data, updating obsolete data, and similar operations.

目录操作包括把新数据保存到目录，搜索和检索保存的数据，删除不需要的数据，更新过时数据，以及类似的操作。

youdao

Such a'radio' receiver would require far fewer and less complex structures than awarehouse capable of storing and retrieving a lifetime of data.

与一个存储及追忆一生数据的仓库来说，这个“收音机”只要求很少以及复杂度很低的组成结构。

youdao

Retrieving and storing data from a hard-disk drive takes one million times longer than accessing it from server memory, a difference that can severely degrade application performance.

FORBES: Bridging The Data Deluge Gap

The challenge is storing, retrieving and prioritizing unprecedented volumes of data.

FORBES: To Manage Big Data, You Need Smarter Storage