For one of my university modules this term, we have been tasked to design and develop a substantial piece of software in groups. One part of the system I have been assigned is the database. UML is taught as part of the module content, and we are encouraged to include diagrams in the design document, so I decided to make an Entity-relationship model of the database I made.
I briefly considered using a GUI UML editor to produce this diagram, but quickly decided this would be a painfully slow and laborious task. Instead, I searched for a tool that could generate UML diagrams from plain text.
Why Text?
I am a programmer, so I’m highly experienced working in plain text, having spent countless hours in Emacs and Vim manipulating code in various ways. As such, I find it more comfortable to work with a (well-designed) textual “language” than with a GUI. Here are a few concrete advantages:
- Copy and Paste: If I want to create multiple similar parts of the diagram, I can simply copy-paste the relevant code.
- Find and Replace: Easy renaming etc.
- Version Control (with Git): While some GUI apps probably save in a “plain text” format like XML, the fact that I wrote the text would mean a clear correspondence between the changes made in a commit and the diffs on the file.
- Separation of Content and Form: This is the big one that the LATEX
buffs like to wheel out. Since the main text is an abstract
description of what the
documentdiagram content should be, the layout and appearance are determined at compile-time. This means I can change the colour or font of all objects of the same type, completely reorient the diagram and change the shape of lines connecting entities all with just a few lines of code.
PlantUML vs Similar Tools
Many more general graphics description languages exist; here are just a few:
- Pic: a general diagram drawing tool that integrates with (g|t)roff;
- Tikz: A LATEX package;
- Graphviz: Specialised for (vertex and edge) graphs. Used by PlantUML as a backend;
- METAPOST, and the relevant MetaUML package for it, which primarily targets PostScript.
The problem with these tools is that they inherently aren’t specialised. For my A-Level programming project write-up, I used METAPOST with MetaUML to draw a class hierarchy with a piddly 9 classes, which despite seemingly being specialised to UML required manual positioning of the class boxes (At least it supported relative positions!) and as such was a massive pain to use. I used Tikz for drawing flow charts in the same document, and despite effectively building a specialised flow chart drawing library on top of it, had to manually override the spacing of objects in many instances.
On the other hand, within about 40 minutes, I went from installing PlantUML to creating the diagram for all 13 tables in the database, spread out beautifully and automatically, and with not so much as a relation arrow overlapping.
I’m not going to put the image here for plagiarism concerns; contact me in a year’s time if you want to see it, since the coursework changes every year. You can search online for examples of the results you can get with PlantUML. It gets my highest recommendation!