Implicit NNSPs

When a context does not want to use part of its namespace for junctions, it uses implicit NNSPs for federating subordinate naming systems. An implicit NNSP is named using the XFN component separator. For example, the name wiz.com/ names the implicit NNSP of wiz.com. Each context can have one implicit NNSP.

Composite name resolution involving implicit NNSPs proceeds as follows, depending on whether the context supports strong or weak separation.

A context that supports strong separation and resolves composite names using an implicit NNSP consumes the first component of the composite name supplied to it. Any remaining components are resolved in the context pointed to by the implicit NNSP of the first component.

A context that supports weak separation and implicit NNSPs in its implementation needs to distinguish the use of the XFN component separator character as an XFN component separator or an atomic separator. This means that such a context needs to know when to exit the current (native) naming system and follow the NNSP. This can be achieved using a static, syntactic policy or a dynamic, resolution-based policy.

With the syntactic policy, a context syntactically discovers where the boundary between its naming system and the subordinate naming system lies. This can impose certain restrictions on the syntax of subordinate naming systems. Subordinate naming systems must not permit, as valid top-level names, that are syntactically indistinguishable from names allowed in the superior naming system. For example, assume the superior naming system has a name syntax whose distinguishing feature is that each atomic part must have an equal sign (=). The superior naming system might impose as a policy that subordinate naming systems must not have top-level names with an equal sign in them. Resolution in the superior naming system continues until all leading components of the supplied composite name fitting the syntactic rule are consumed. Any remaining components are resolved in the context of the NNSP of the last component fitting the syntactic rule.

If a context is not able to syntactically differentiate between atomic components and composite name components, or does not want to impose any syntactic restrictions, it might be able to determine the naming system boundary at runtime, during resolution. The policy is to continue resolution in the current naming system until resolution fails, at which point the implicit NNSP associated with the last context at which resolution succeeded is used to continue the resolution. A conflict arises if the same atomic name is bound both in the last context and the context pointed to by the last context's implicit NNSP. In this case, the binding in the last context takes precedence. This way of supporting weak separation requires the context to have the capability of returning remaining unresolved parts of a given name.