Defines a subtype of {@link Oid} specific to a root adapter.
The root adapter/pojo can be recreated with no further information; the {@link #getObjectSpecId()} can be used to fetch the corresponding{@link ObjectSpecification} using {@link SpecificationLoaderSpi#lookupBySpecId(String)}.
As such, is directly akin to the DSP's oid that is of the form CUS|1234567A, where the overall form is a simple string and also identifies the type of the object.
In addition, can be directly encoded/decoded into strings. The {@link #enString(OidMarshaller)} interfaceis defined in the interface; implementations must also provide a static deString(String) factory method.