Chapter 2: Visual notation and graphical user interface for rule creation

Manually creating knowledge graph generation rules requires a substantial amount of human effort. Therefore, the use of rules by users remains complicated. To this end, a significant number of tools with a graphical user interface (GUI) were implemented to facilitate rules creation and updating, such as Map-On, the fluidOps Editor, and RMLx. However, the design of these tools and their GUIs are not thoroughly investigated yet:

• no visual specification is available, while this increases the visualization's adoption by other tools; none of the tools tackle
• the scalability issues that accompany the use of graphs for visualizations;
• the visualization of heterogeneous data sources, besides showing the raw data; and
• the integration of transformations of the data sources in the visualizations of the rules.

This chapter presents our following contributions to rule creation:

• the initial version of the RMLEditor (see Section 2.1): our software tool to create and update rules using graph-based visualizations;
• MapVOWL: our visual notation for knowledge graph generation rules (see Section 2.2); and
• the updated version of the RMLEditor (see Section 2.2).

We address Research Question 1 "How can we design visualizations that improve the cognitive effectiveness of visual representations of knowledge graph generation rules?" and Research Question 2 "How can we visualize the components of a knowledge graph generation process to improve its cognitive effectiveness?" and validate Hypothesis 1 "MapVOWL improves the cognitive effectiveness of the generation rule visual representation to generate knowledge graphs compared to using RML directly," and Hypothesis 2 "The cognitive effectiveness provided by the RMLEditor's GUI improves the user's performance during the knowledge graph generation process compared to RMLx."

As this is a cumulative dissertation, both Sections 2.1 and 2.2 correspond with a publication. Section 2.1 corresponds with "RMLEditor: A Graph-Based Mapping Editor for Linked Data Mappings". Section 2.2 corresponds with "Specification and Implementation of Mapping Rule Visualization and Editing: MapVOWL and the RMLEditor".