2 intensive weeks for Data Modeling course at the end of my 3rd semester. So so tired now 
Just search for an easy tool to draw model for homework 2 and found some as below:
1. yEd: free, java application (need to install Java VM first). It supports only few diagrams, but support user-defined shapes & diagrams
Link: http://www.yworks.com/en/products_yed_about.html
2. Dia: the same as yEd, but it is open-source and support quite a lot kinds of diagram.
Link: http://dia-installer.de/index_en.html
Aditional Features:
- DiaShape: support to download addition shapes for Dia.
- Dia2Code: generates code from an UML Dia Diagram. Currently supported languages are: Ada, C, C++, C#, IDL, Java, PHP, PHP5, Python, Ruby, shapefiles and SQL
3. Umbrello: (has not tested because it runs on Linux)
Link: http://uml.sourceforge.net/index.php
4. TreeForm: an easy drawing tool for trees, flowchart,…It’s a java application (need to install Java VM first)
Link: http://sourceforge.net/projects/treeform/
5. Topcased: is a meta-tool to develop your own graphical editor and model transformation. It’s open-source and need to be used with Eclipse.
Link: http://www.topcased.org/index.php/
I’m currently using Dia. It’s free, portable, and support many kinds of diagrams that I need.
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