現在介紹幾個相對比較好用的工具：
第一個：ERDesigner NG
官方網址是：http://mogwai.sourceforge.net/?Welcome:ERDesigner_NG
屬於sourceforge的一個開源產品，目前版本為1.4
以下是官方所描述的：
程序代碼
The Mogwai ERDesigner is a entity relation modeling tool such as ERWin and co. The only difference is that it is Open Source and does not cost anything. It was designed to make database modeling as easy as it can be and to support the developer in the whole development process, from database design to schema and code generation. This tool was also designed to support a flexible plug in architecture, to extend the system simply by installing a new plug in. This way, everybody can implement new features and tools to make ERDesigner fit the requirements.
官方網址是：http://mogwai.sourceforge.net/?Welcome:ERDesigner_NG
屬於sourceforge的一個開源產品，目前版本為1.4
以下是官方所描述的：
程序代碼
The Mogwai ERDesigner is a entity relation modeling tool such as ERWin and co. The only difference is that it is Open Source and does not cost anything. It was designed to make database modeling as easy as it can be and to support the developer in the whole development process, from database design to schema and code generation. This tool was also designed to support a flexible plug in architecture, to extend the system simply by installing a new plug in. This way, everybody can implement new features and tools to make ERDesigner fit the requirements.
ERDesigner NG
* is based on Java and can be run on Windows and Unix systems
* has a powerfull WYSIWYG for physical database design
* handles tables, relations, indexes and comments
* supports subject areas
* supports MySQL, oracle, Microsoft SQLServer and Postgres
* creates the SQL DDL statements for schema creation
* has an integrated schema version control system
* can generate schema migration scripts for every change
* stores the database definition as XML files for further processing
* can export the database schema as GIF, BMP, JPEG or SVG files
* has an integrated reverse engineering module for existing schemas
* it is based on GPL license
* support is available by authors and newsgroups
從上述的描述我們可以看得出，軟件支持多種主流的數據庫，比如mysql、oracle、MSSQLSERVER等。
功能方面支持反向工程、數據庫比較、通過建模自動產生ddl、將模型圖導成圖片等等。
軟件的截圖如下：
第二個：ModelRight3
官方網址為：http://www.modelright.com/Default.aspx
以下是官方的介紹：
程序代碼
Need to design, visualize or document your database?
ModelRight 3 can reverse engineer your existing database to give you a graphical view of it, generate all the SQL statements to create the database, or synchronize your database model with the database to keep your design up to date.
Do you need to control the most detailed aspects of your database?
ModelRight 3 has more complete and in-depth support for your database's (Oracle, SQL Server, MySQL or any via ODBC) most advanced features.
別以為真的支持這么多數據庫，這個是專業版的才知識這么多，如果你叫錢多多，那你就去買專業版吧！
這個產品是比ERDesigner NG專業的一個，理由非常簡單，它本身就是一個商業的工具，不過，也有免費版本，只是免費版權在數據庫的支持上少了好多！今天我們介紹的就是這個免費版本，只支持mysql，比較痛苦！產商其實不太厚道！
下個圖片截圖吧！
再來個官方的圖片（專業版的）
看了專業版的千萬不要眼紅，使用是要付出代價的！如果我們每個人都是錢多多，多好啊！
第三，OpenSystemArchitect（推薦產品）
官方網址是：http://www.codebydesign.com/
這是一個開源做得比較徹底的一個產品，推薦大家使用。
最喜歡的一點說法是操作習慣有點類似於PowerDesigner，界面比PD丑一點，但是，還挺好用的！
它支持windows、Linux
以下是官方的介紹：
程序代碼
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，看完這些截圖之后，我相信你馬上會下載一個用用！ 為什么，確實是厚道！
Logical Model
Physical Model
SQL Editor
第四個：Mysql WorkBench
官方網址：http://dev.mysql.com/workbench/
Mysql官方出的設計工具，for mysql
如果你是使用mysql，也可以考慮一下它！