  An increasing number of organisations in almost all fields have started
adopting semantic web technologies for publishing their data as open, linked
and interoperable (RDF) datasets, queryable through the SPARQL language and
protocol. Link traversal has emerged as a SPARQL query processing method that
exploits the Linked Data principles and the dynamic nature of the Web to
dynamically discover data relevant for answering a query by resolving online
resources (URIs) during query evaluation. However, the execution time of link
traversal queries can become prohibitively high for certain query types due to
the high number of resources that need to be accessed during query execution.
In this paper we propose and evaluate baseline methods for estimating the
evaluation cost of link traversal queries. Such methods can be very useful for
deciding on-the-fly the query execution strategy to follow for a given query,
thereby reducing the load of a SPARQL endpoint and increasing the overall
reliability of the query service. To evaluate the performance of the proposed
methods, we have created (and make publicly available) a ground truth dataset
consisting of 2,425 queries.
