The advent of Linked Data is spurring the deployment of applications that use the RDF data model at the information tier. In addition to querying RDF data, there is also the requirement for online updates with suitable concurrency control. Client sessions in Web applications are organized as transactions involving requests that read and write shared data. Executing concurrently, these sessions may invalidate each other's data. This paper presents a locking model, which is a variant of multigranularity locking protocol (MGL), to address isolation between transactions that manipulate RDF data. Four "hierarchically'' related granules are defined, as well as new read/write operations and their corresponding lock modes, specifically created for the RDF data model. These new operations allow greater concurrency than the classical read/write operations in relational databases. We assessed the performance of the proposed locking model through model simulation. (C) 2016 Elsevier B.V. All rights reserved.