# How Many and What Types of SPARQL Queries can be Answered through Zero-Knowledge Link Traversal?

## TL;DR

This paper analyzes which SPARQL queries can be answered via zero-knowledge link traversal, proposes methods to identify and transform such queries, and evaluates their efficiency and limitations in real-world scenarios.

## Contribution

It introduces a method to determine if SPARQL queries are answerable through link traversal without endpoints and provides algorithms to transform and evaluate these queries.

## Key findings

- A significant portion of real queries can be answered via link traversal.
- Transforming answerable queries improves query efficiency.
- Limitations exist for complex query patterns in zero-knowledge link traversal.

## Abstract

The current de-facto way to query the Web of Data is through the SPARQL protocol, where a client sends queries to a server through a SPARQL endpoint. Contrary to an HTTP server, providing and maintaining a robust and reliable endpoint requires a significant effort that not all publishers are willing or able to make. An alternative query evaluation method is through link traversal, where a query is answered by dereferencing online web resources (URIs) at real time. While several approaches for such a lookup-based query evaluation method have been proposed, there exists no analysis of the types (patterns) of queries that can be directly answered on the live Web, without accessing local or remote endpoints and without a-priori knowledge of available data sources. In this paper, we first provide a method for checking if a SPARQL query (to be evaluated on a SPARQL endpoint) can be answered through zero-knowledge link traversal (without accessing the endpoint), and analyse a large corpus of real SPARQL query logs for finding the frequency and distribution of answerable and non-answerable query patterns. Subsequently, we provide an algorithm for transforming answerable queries to SPARQL-LD queries that bypass the endpoints. We report experimental results about the efficiency of the transformed queries and discuss the benefits and the limitations of this query evaluation method.