The permission propagation constraint improves the access control grain. It makes the grain reach element or attribute level.
权限传递约束提高了访问控制的粒度，使得访问控制的粒度能够达到元素或属性级。
Authorization constraint is an important part in role-based access control models.
授权约束是基于角色的访问控制模型中一个非常重要的部分。
RBAC is rather difficult to assign permissions to roles reasonably and is unable to express constraint in complicated workflow access control.
RBAC在工作流访问控制的应用中很难合理地为角色配置权限，而且无法表达复杂的工作流访问控制约束。
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