Providing efficient access to XML documents is crucial, as XML has become the most important technique to exchange data in WWW. DOM is a popular object-oriented user interface to manipulate XML documents. Several concurrency control protocols have been proposed for DOM by analyzing the read/write behaviors of DOM operations. However, none of them exploit the semantics of DOM operations for enhancing concurrency. Semantics were introduced in object databases to develop concurrency control protocols. And this research is motivated by the success of this approach on object databases. In this paper, we analyze the commutativity relationship between DOM operations and propose a new semantic-based protocol for DOM, namely the SCD protocol. SCD not only allows non-serializable schedules to be executed, but also preserves the correctness of the resulting schedules. Our simulation results show that SCD outperforms other DOM-based protocols in its higher throughput and shorter response time. There are two major contributions in this paper. First, the semantics of DOM operations are analyzed formally. Second, based on the semantic analysis, a new way to design DOM-based concurrency control protocol is presented.