1. 第四维(4D)：
第四维是由 Laurent Ribardière 开发的关系数据库管理系统和 IDE。 4D 可以作为服务器运行，以便多个客户端可以管理单个数据库。 4D 创建于 1984 年，并于 1987 年为 Macintosh 稍微推迟了公开发布。它是一个具有集成数据库管理系统的应用程序开发环境。
2.阿里云云数据库PolarDB：
云数据库PolarDB是一个兼容MySQL、PostgreSQL、Oracle的云原生关系型数据库。云数据库架构在单个集群中支持 5000 台物理机。它专为需要快速性能、高并发和自动扩展的业务关键型数据库应用程序而设计。
4D与阿里云PolarDB的区别：
| S.NO. | 4D | Alibaba Cloud ApsaraDB for PolarDB |
|---|---|---|
| 1. | Developed By 4D, Inc in 1984. | Developed By Alibaba in August 2013. |
| 2. | It is an application development environment with an integrated database management system. | It is a cloud-native relational database compatible with MySQL, PostgreSQL, and Oracle. |
| 3. | Server operating systems for 4D are OS X and Windows. | In Alibaba Cloud ApsaraDB for PolarDB, Hosted server operating systems. |
| 4. | It is not available as a cloud service. | It is available as a cloud service. |
| 5. | It does not support In-memory capabilities | It supports In-memory capabilities. |
| 6. | The programming language supported is PHP. | The programming languages supported are Java and Python. |
| 7. | There is no Partitioning method. | There is only one partitioning method – Sharding. |
| 8. | APIs and other access methods supported are ODBC, RESTful HTTP API and SOAP web-services | APIs and other access methods supported are JDBC and ODBC. |
| 9. | It support only one replication methods – Master-master replication. | It also support replication methods. |