Extended UML class diagram constructs for Visual SPARQL queries in ViziQuer/web

Visual notations based on customized entity relationship and basic UML class diagram paradigm of classes, associations and attributes are successfully used in data modeling and data querying alike, both in relational database and in semantic/conceptual model setting. We propose a number of constructs for extending the basic diagrammatic framework in the setting of visual specification of SPARQL select queries for enabling visual specification of hierarchic data instance and aggregated queries. Our proposal includes: (i) a visual notation for subqueries, (ii) separate lists of aggregated and grouping attributes in aggregated queries, (iii) query control nodes (unit and union) not corresponding to data instances, and (iv) integration with textual SPARQL fragments. We report on an initial user study validating the understandability of the subquery notion by users without specific IT training, as well as announce implementation of the proposed notation constructs in a web-based diagrammatic (multi-modal) query tool.