Towards an Extensible Web-Based Open-Source Graphical Ontology Editing Framework

Abstract

We describe work in progress towards an 1) extensible, 2) web-based, and 3) open-source ontology editor. The domain logic is the same as in our classical desktop-based graphical ontology editor OWLGrEd. Thus, we are bringing the same set of features to the web environment. Moreover, it becomes possible to implement additional web-based features, such as collaborative editing and integration with third-party applications.

Keywords

• OWLGrEd ontology framework

-

web graphical ontology editor extensible

Introduction

In OWLGrEd, most OWL constructs have a one-to-one mapping to UML constructs (e.g., OWL classes map to UML classes, while OWL properties map to UML associations and attributes). OWLGrEd has a compact syntax, where unnecessary anonymous classes are not visualized. The main strength of OWLGrEd is the ability to tune graphical presentations to meet various speci c needs. For instance, domain-speci c pro les can be used to modify graphical elements depending on their annotations (e.g., to specify a diamond shape at one end of the connector for UML-like compositions or to alter shapes of particular classes) [ 2 ]. The visual appearance of elements (such as their shapes and colors as well as the layout and structure) can be changed either manually, or programmatically via prede ned or user-de ned extensions [ 4 ].

Our goal is to retain the same set of features as in the web-based OWLGrEd. 3

Moving OWLGrEd to the Web

To simplify the transition to the web and to minimize the maintenance costs of existing OWLGrEd features, we retained the code implementing the domain logic in the classical desktop OWLGrEd. However, we still had to perform the next two steps.

First, we had to move to the web browser the two main UI components, the graph diagram editor and the dialog engine (see Figure 1).4 Both components are essential for a typical scenario: the user starts with an empty diagram or imports an existing ontology, then adjusts the diagram incrementally (by adding, moving, and deleting diagram elements and by specifying their properties in dialog windows), and nally exports the ontology in some serialization format. 4 We use the ajoo library for editing graph-like diagrams [ 13 ]. We use the DoJo Toolkit for visualizing dialog windows, https://dojotoolkit.org/.

The graph diagram editor relies on an advanced layout algorithm to obtain the initial layout (e.g., to arrange the whole diagram hierarchically, symmetrically, or universally) as well as to adjust the existing layout incrementally while the user edits the diagram [ 5 ]. The dialog engine, in its turn, uses a variation of the same algorithm to visualize GUI dialogs on-the- y (some of them can be generated by OWLGrEd extensions at runtime) [ 7 ].

Second, we had to deal with network-related issues such as user management, connection management, data synchronization, and client-server code interoperation. For that, we rely on webAppOS5, our open-source cloud-based infrastructure for developing and running web applications [ 8 ]. The infrastructure was specially designed for migrating existing standalone applications by providing a single-PC illusion for them. OWLGrEd is a guinea pig within the webAppOS project. All client-side and server-side code interoperation is factored out by webAppOS. Besides, webAppOS provides a means to upload, download, and open OWLGrEd projects in a way similar to Windows Explorer or macOS Finder. Existing ontologies (.owl les) can be imported into the web-based OWLGrEd and exported back in the desired serialization format by means of the web-based \Browse for le" and \Save as" dialogs, which provide the same user experience as in the classical desktop-based OWLGrEd. 4

Bringing Additional Features

In webAppOS, data can be synchronized not only between the server and the client but also with other authorized clients (e.g., debuggers or third-party applications). Thus, the full OWLGrEd project currently being edited (including all ontology diagrams) can be manipulated from the outside via a web socket using a documented protocol. One of such third-party applications can be a collaborative bot for synchronizing diagrams between multiple editors.

Similar features have already been o ered by WebProtege, which uses a proprietary webhooks-based service Slack6 for that [ 6 ]. Our goal is not to compete, but complement WebProtege with the ability to edit ontologies graphically. We are considering the idea of using WebProtege as domain storage for ontologies being edited graphically in the web-based OWLGrEd. 5

The Demo

The web-based OWLGrEd is expected to be fully open-source, with the ability to launch it on a private server or as a cross-platform standalone desktop application, with no technical and licensing obstacles of the classical OWLGrEd.

The demo re ecting the current work in progress can be found at http: //webappos.org/owlgred. We show how to 1) import and adjust an existing ontology; 2) create an ontology from scratch and export it to an .owl le; 3) 5 http://webappos.org 6 https://slack.com manipulate the diagram programmatically from the outside; 4) upload and open an OWLGrEd project from the webAppOS desktop.

Acknowledgments. The work has been supported by European Regional Development Fund within the project #1.1.1.2/16/I/001, application #1.1.1.2/VIAA/1/16/214 \Model-Based Web Application Infrastructure with Cloud Technology Support".

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