E-R diagram Drawing Tools
by Cao Qing
E-R model is a powerful tool for database design, and E-R diagram is a powerful for E-R modeling. Then how can we draw E-R diagrams efficiently and effectively? When preparing our group lecture for E-R model, we used several drawing software and finally we choose yED, a simple and free drawing tool. Today we want to talk about yED and other commonly used software to draw E-R diagrams. Hope it will be of some help to you.
1.1. How to install yED
yED is a free software developed by yWorks company and everyone can download it from its official website: http://www.yworks.com/en/products_yed_download.html.
The installation is just a few minutes’ work.
1.2. Draw E-R diagram by yED
The working environment for yED is clean and easy to use, as shown in the following figures.
After start yED, just choose “New Document” on the welcome screen or “File>New” and you can start drawing.
yED provides you with many kinds of graphs. In this blog, only E-R diagram will be talked about in details. Let’s start to draw an E-R diagram now!
(1) Open the palette for E-R diagram
Choose “Entity Relationship” in the Palette to open the list of E-R diagram components, as shown in Fig. 1.
Fig 1. Open the list of E-R diagram components
(2) Add components to the drawing area
There are two ways to add shape components (rectangles, ellipses, diamonds and so on).
First, we can double click the component to choose it as the default, then click the point where you want to put the component in the drawing area.
The second way is to drag the component you want and release your mouse to put it on the drawing area.
After you have put several entity sets on the drawing area, you can connect them together using lines including the notations indicating the mapping cardinality. Just double click the lines under the shapes to set it as default. Click one of the shape, say Entity_1, keeping the left button on and move to the destination shape, Relationship_A, and then release the mouse and the line is completed. To complete a binary relationship, another line is required and we choose a linetype with a (zero-or-many) notation, as shown in Fig. 2.
Fig 2. Add components to the drawing area.
In yED, you can select one shape and one linetype as defaults at a certain time.
To make the diagram more beautiful, you may want to change colors of the shapes and lines and the style and size of fonts inside the shapes. This is easy to do in the Properties View, as shown in Fig 3.
Fig3. Make the appearances more appealing!
yED contains almost all the components of E-R diagram, including the double ellipse for multivalued attribute, the dashed ellipse for derived attribute, the double diamond for weak relationship and so on. Extended features of E-R diagram are not directly contains in yED, and if you want to draw an EER (extended entity-relationship) diagram, you may use the shapes (such as a triangle for specialization) of other classifications.
yED is very outstanding in drawing E-R diagram but it has nothing to do with the data and database: it just draws a model for you, but the database doesn’t exist. Now let’s introduce other drawing tools that can draw the model and establish the database at the same time.
2. Other Software
Free software for drawing E-R diagram and establish database at the same time includes MySQL Workbench (and its predecessor DB Designer), Rise Editor and so on. The former has been introduced in one of Cao Qing’s blogs. Following is a snapshot of Rise Editor.
Fig.4. Snapshot of RISE Editor
The usage is similar to that of yED: just drag a component and put it where you like.
The shapes are much fewer in RISE Editor than in yED, but RISE editor can establish the interactions among all the components. So yED concerns more about model display and RISE Editor concerns more about data and database.
Besides, there are also many other powerful tools you can use to do E-R modeling, but you may need to pay some money for them. The tools include Sybass Power Designer, IBM Rational Rose, MS Visio and so on.
Which tool to choose depends on the particular needs: if you just want to draw E-R diagrams, then yED is a good choice for its various components and easy use. However, if you want to establish the database along with E-R diagram drawing, then you may need to use other tools according to which database developer you are using. For example, if you are using MySQL, then MySQL Workbench may be a good choice, because you can easily convert your diagrams into tables in the database of MySQL.
We ourselves are fresh users to these tools and we hope we can discuss more about E-R diagram drawing tools with you guys~