What are real SPARQL queries like?

Abstract

We present statistics on real world SPARQL queries that may be of interest for building SPARQL query processing engines and benchmarks. In particular, we analyze the syntactical structure of queries in a log of about 3 million queries, harvested from the DBPedia SPARQL endpoint. Although a sizable portion of the log is shown to consist of so-called conjunctive SPARQL queries, non-conjunctive queries that use SPARQL's union or optional operators are more than substantial. It is known, however, that query evaluation quickly becomes hard for queries including the non-conjunctive operators union or optional. We therefore drill deeper into the syntactical structure of the queries that are not conjunctive and show that in 50% of the cases, these queries satisfy certain structural restrictions that imply tractable evaluation in theory. We hope that the identification of these restrictions can aid in the future development of practical heuristics for processing non-conjunctive SPARQL queries.

Complexity and Expressive Power of Weakly Well-Designed SPARQL

“…We challenge this belief by answering differently the question on the prevalent structure of real-life queries beyond the well-designed fragment. This question is not just of theoretical interest: as previous studies [34] show (and our analysis confirms), about half of queries with OPT asked over DBpedia are not well-designed. Next we discuss two sources of non-well-designedness in patterns as revealed by the example queries (2) and (3) in the introduction-one based on OPT and another one on FILTER.…”

“…In particular, we now know much about evaluation [1,3,4,6,8,20,22,23,25,28,34,38], optimisation [8,9,12,13,24,27,35], federation [10,11], expressive power [2,20,21,25,36,39], and provenance tracking [15,16] for queries from various fragments and extensions of SPARQL. These studies have had a great impact in the community, in fact influencing the evolution of SPARQL as a standard.…”

“…To answer this question, a comprehensive analysis of real-life queries is required. We are aware of two works that analyse the distribution of operators in SPARQL queries asked over DBpedia [7,34]. Both studies show that OPT is used in a non-negligible amount of practical queries.…”

“…Both studies show that OPT is used in a non-negligible amount of practical queries. However, only Picalausa and Vansummeren [34] go further and analyse how many of these queries are well-designed; and the result is quite interesting-welldesigned queries make up only about half of all queries with OPT. In other words, well-designed queries are common, but by far not exclusive.…”

LSQ: The Linked SPARQL Queries Dataset

“…The data can be used by researchers to conduct analyses of features used in real-world SPARQL queries [3,10,11]. UC3 Caching Works on caching [14,8] could benefit from a dataset of real-world queries by, e.g., analysing real-world sequences of queries.…”