# Providing a Custom Permission Authority

Both read and write operations on the model are executed through an accessibility layer called the model accessor, implemented by `org.eclipse.sirius.ecore.extender.business.api.accessor.ModelAccessor`. Each session has an an associated `ModelAccessor` which can be obtained with `Session.getModelAccessor()`.

The model accessor itself delegates the permission checking to an `IPermissionAuthority` , which is responsible for checking which operations are permitted on a given model element. The permission authority is also used to lock model elements (both representation and semantic elements), query their lock status and be notified (through `IAuthorityListener`) when a lock is taken or released.

You can provide a custom permission authority by implementing the interface `org.eclipse.sirius.ecore.extender.business.api.permission.IPermissionAuthority` and registering your custom implementation with the `org.eclipse.sirius.ecore.extender.PermissionProvider` extension point.