免费的数据库建模工具

OpenSystemArchitect（推荐产品）
官方网址是：http://www.codebydesign.com/
这是一个开源做得比较彻底的一个产品，推荐大家使用。
最喜欢的一点说法是操作习惯有点类似于PowerDesigner，界面比PD丑一点，但是，还挺好用的！
它支持windows、Linux
以下是官方的介绍：

程序代码

Open System Architect (OSA) is an application used for modelling a system. OSA currently supports data modelling (physical and logical) with UML in the works. The unique thing about OSA is that it is an Open Source product licensed under the General Public License (GPL). The free factor makes OSA particularly interesting for students but OSA is powerful enough to compare favourably with products costing thousands of dollars.

OSA is sponsored by CodeByDesign (the originally developer of OSA) and by Source Forge (they host the community collaboration environment for OSA).

以下是官方的demo，看完这些截图之后，我相信你马上会下载一个用用！ 为什么，确实是厚道！
Logical Model


Physical Model


SQL Editor