I recently came across a post by Michael Hoogkamer about his Termboard RDF/OWL graph visualization tool. It was perfect timing, because over the past few days I’ve been exploring various RDF/OWL knowledge-graph applications and databases. I’ve been experimenting with the W3C standards since 2013, and it honestly surprised me that even after a decade, or two decades since the implementation of W3C semantic web technology stack, there is still no straightforward way to visualize an ontology’s data model: the relationships between classes, the object properties linking those classes, and the data properties defined on each class.
Let me say this clearly: for database professionals, being able to see the data model and explain it easily to others in the company is essential. You need to visualize both the graph data model (the TBox) and the network of instances (the ABox) in parallel, not merged into a single graph, to properly understand how the model is applied in a specific scenario. This is similar to relational databases, where you examine the schema (tables and relationships) separately from the actual data stored in those tables.
Kudos to Michael Hoogkamer for recognizing this gap in RDF/OWL visualization tools and addressing it with Termboard. I guess he invested significant effort in researching alternatives before creating Termboard. I want to acknowledge that Termboard is a very good tool: it’s easy to use, offers many options for visually editing your graph, provides multiple layout configurations, lets you select what to display, and supports importing and exporting various ontology formats. However, I ran into issues when trying to import a Turtle ontology, here is my example: https://github.com/athanhat/foo/blob/main/addressbook.ttl
Even after converting it to RDF/XML format using the rapper CLI tool, I still couldn’t load it (https://github.com/athanhat/foo/blob/main/addressbook.owl).
Parsing Error - File does not contain recognizable OWL constructs.
So, I uploaded the same example to demonstrate it with another tool WebVOWL, store the file locally and then from Ontology menu at the bottom select ontology file to upload: https://service.tib.eu/webvowl/#file=addressbook.owl
From the tools I have tested so far, WebVOWL remains the best solution for reading an ontology and producing a clean, ERD-like visualization of the RDF/OWL model. It’s free to use, it has a permissive license, and its source code is available on GitHub all of which make it highly accessible. While Termboard offers many configuration and visualization options, the most important first step in creating an ontology is simply being able to inspect the schema. With the help of AI, parsers, validators, and programming tools, an experienced developer can easily author an ontology file that adheres to the RDF/OWL specifications; therefore, all the visual editing “bells and whistles” become far less important for power users who primarily need a clear, accurate view of the model itself.
I’m genuinely interested to learn what other open-source tools my colleagues and professional network contacts in the field have used to visualize ontologies in the way I’ve described (See the image below for an example of the kind of visualization I’m referring to.).
