SPARQL Federated Query Debugging Tool

Gaining insight into a complex problem often requires combining data from multiple datasets. For this reason, SPARQL query support within a federated environment is an important feature. However, several pitfalls have been encountered in practice, significantly complicating the use of SPARQL queries in such setups. These challenges include uninformative error responses, performance bottlenecks and unintended semantic changes introduced by SPARQL endpoints. To address these pitfalls, this paper introduces a newly implemented SPARQL query debugger, which is available as a web application at https://sparql-debugger.elixir-czech.cz . It has been developed for the purpose of monitoring, in real time, the execution of SPARQL queries that incorporate the service pattern. This monitoring is crucial for error detection and performance optimization. Detailed service execution data (such as SPARQL requests and responses, durations, etc.) can help identify the specific instance of a service responsible for a problem, even if it is deeply nested within the service execution tree. The tool is based on the principle of redirecting all requests to a debugging proxy server, so it can be used with all SPARQL-compliant endpoints without the need for their modification. The debugging tool presented in the paper enables the identification and resolution of issues that are otherwise difficult to address and has proven its effectiveness in practice.