1.第四维度(4D)：
第四维是关系数据库管理系统和由LaurentRibardière开发的IDE。 4D可以作为服务器运行，以便多个客户端可以管理一个数据库。 4D创建于1984年，并于1987年在Macintosh上稍有延迟地公开发布。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.适用于PolarDB的阿里云ApsaraDB：
ApsaraDB for PolarDB是与MySQL，PostgreSQL和Oracle兼容的云原生关系数据库。 ApsaraDB体系结构在单个群集中支持5000台物理机。它是为需要快速性能，高并发性和自动伸缩的关键业务数据库应用程序而设计的。
PolarDB的4D与阿里云ApsaraDB之间的区别：
| 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. |