HP OpenVMS Guide to System Security: OpenVMS Version 8.4 > Chapter 5 Descriptions of Object Classes
Processes that access shared resources can coordinate access using the services of the lock manager. These services allow processes to associate a name with a resource, such as a file or a data structure, to arbitrate access to that resource, and to exchange limited information through a lock value block. The namespaces that catalog resources on which locks can be taken are called resource domains.
A process must become a member of a resource domain to take and release locks and to read and write value blocks associated with resources in that resource domain. A process implicitly joins the system and group domains, but it explicitly joins other domains through a call to the $SET_RESOURCE_DOMAIN system service. Access to all locks and value blocks within a domain is controlled by access to the domain itself.
A resource domain is identified to $SET_RESOURCE_DOMAIN by a longword binary value. However, the name of the resource domain object is a string containing the resource number interpreted in octal surrounded by brackets  or angle brackets <>. Alternatively, the name of the resource domain object can be expressed as an identifier enclosed in brackets or angle brackets. The identifier must translate to a UIC value; the group field of the UIC is used as the resource domain number.