The file loads but the tree is empty
The file probably does not contain the OTV and OWL vocabularies. Check the counter: if it reads 0 concepts, nothing was recognised. Re-export from Tedi including the OTV vocabulary.
Web application
OTV Ontology Viewer
Load an ontoterminology and read its conceptual hierarchy as a tree: expand and collapse branches, switch between the concept hierarchy alone and the hierarchy with its instances, and export a standalone copy you can share.
Overview
OTV is the simplest tool in the suite, and deliberately so. It does one thing: it takes an ontoterminology and shows you its structure as a navigable tree. There is no editing, no querying and no configuration — upload a file and read it.
That makes it the right tool for a specific moment: you have an
.rdf file exported from Tedi and you want to
see the shape of the concept hierarchy before deciding what to do with it. The
RDF Graph Viewer would draw the same file as a
network; OTV draws it as a hierarchy, which is usually what you want for an
ontoterminology because the hierarchy is the point.
The counter under the file picker reports how many concepts and objects were found, so you can confirm the file parsed as expected before reading anything into the tree.
Requirements
| Browser | Any current Chrome, Firefox, Edge or Safari |
|---|---|
| Installation | None |
| Input | An OTV/RDF file containing the OTV and OWL vocabularies |
Loading a file
Use Upload a OTV/RDF file to choose a file. Until one is selected the viewer reads No file selected and the counter shows 0 concepts, 0 objects.
The file must contain OTV and OWL: this is not a general-purpose RDF viewer. It reads the OTV vocabulary specifically, which is what an ontoterminology exported from Tedi carries. An arbitrary RDF file will not display.
All our published datasets are built this way, so any of them can be downloaded from Zenodo and opened here directly.
The two views
| isA | The concept hierarchy alone: every concept and its generic parent, and nothing else |
|---|---|
| isA + instanceOf | The same hierarchy with the individuals attached to the concepts they instantiate |
The distinction matters more than it looks. isA gives you the abstract
structure — the classification a terminologist built. Adding
instanceOf shows how densely each concept is populated, which is a
different question and usually a much larger tree.
Navigating the tree
| Zoom + / Zoom − | Scale the tree in and out |
|---|---|
| Expand all | Open every branch at once |
| Collapse all | Close every branch back to the roots |
| Rotate | Change the tree's orientation |
| Space + / Space − | Increase or reduce the spacing between nodes |
| Reset | Return to the default view |
On a large ontoterminology, Collapse all then opening one branch at a time is usually more readable than expanding everything. Space and Rotate exist mainly to make a tree fit a screen or a page .
Standalone export
Generate standalone version produces a self-contained copy of the current view that works without the viewer.
This is the feature worth knowing about. It means a concept hierarchy can be sent to a colleague, attached to a paper, or published alongside a dataset, and it will still be explorable by someone who has never heard of OTV and has nothing installed.
Troubleshooting
The tree is unreadable after Expand all
Collapse all, then open one branch at a time. Reduce the spacing with Space −, or switch from isA + instanceOf back to isA to drop the individuals.
Individuals are missing
The isA view shows concepts only. Switch to isA + instanceOf.
Licence & credits
Written by Prof. Christophe Roche, TALOS ERA Chair Holder, University of Crete, within the Horizon Europe project grant agreement 101087269.
Licence
Released under the PolyForm Noncommercial 1.0.0. You may use, modify and share it for any purpose that is not primarily intended for commercial advantage or monetary compensation: research, teaching and personal use all qualify. Copies and modified versions must carry the licence and the notices that came with them. The software is provided as is, without warranty.
PolyForm Noncommercial is a source-available licence rather than an open source one: the noncommercial restriction is not permitted under the Open Source Definition.
Citation
Roche, C. (2025). OTV Ontology Viewer (1.0).
TALOS AI4SSH Laboratory, University of Crete.
https://tools.talos-lab.eu/OTV_Ontology_Viewer/.