In this document, I present the main notions of NoSQL databases and compare four selected products (Riak, MongoDB, Cassandra, Neo4J) according to their capabilities with respect to consistency, availability, and partition tolerance, as well as performance. I also propose a few criteria for selecting the right tool for the right situation.

翻译：在这份文件中,我介绍了NOSQL数据库的主要概念,并根据四个选定产品(Riak、MongoDB、Cassandra、Neo4J)在一致性、可用性、分隔容忍度和性能方面的能力,对四个产品(Riak、MongoDB、Cassandra、Neo4J)进行了比较,我还提出了选择正确情况的适当工具的几个标准。