In recent years, data spaces have emerged as a framework for secure data collaboration. Data spaces are distributed data collaboration infrastructure systems that enable data collaboration among stakeholders. One of the requirements for data space systems is the technical enforcement of governance policies for the shared data. The objective of this study is to propose a new policy definition language, DSPOL, as a stepping stone toward realizing the enforcement of data governance for the practical use of data spaces. DSPOL can describe the constraints that must be followed in data space systems when accessing and using data, and when distributing deliverables. It has verification and validation functions to ensure that the policy description is as the writer intended and that there are no inconsistencies in the policy. We defined the state transitions of data usage in data user environments, developed a model of the execution infrastructure in data space systems, and formulated the contents of the describable policies. We implemented DSPOL and its verification and validation functions. Examples of policy descriptions based on supposed scenarios were shown, and examples of verification and validation were presented.