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NAME
     xfn_links - XFN links: an overview of XFN links

DESCRIPTION
     An  XFN link is a special form of reference that contains  a
     composite  name, the  link name, and that may be bound to an
     atomic name in an XFN context. Because the link  name  is  a
     composite name, it may span multiple namespaces.

     Normal resolution of names in context operations always fol-
     lows  XFN  links.   If the first composite name component of
     the link name is the atomic  name  ".",  the  link  name  is
     resolved  relative to the same context in which  the link is
     bound, otherwise, the link name is resolved relative to  the
     XFN  Initial Context of the client. The link name may itself
     cause resolution to pass through other XFN links.
      This gives rise to the possibility  of  a  cycle  of  links
     whose  resolution could not terminate normally.  As a simple
     means to avoid such non-terminating resolutions, implementa-
     tions  may define limits on the number of XFN links that may
     be resolved in any single operation invoked by the caller.

     These are the interfaces:

     #include <xfn/xfn.h>

     FN_ref_t *fn_ref_create_link(const FN_composite_name_t *link_name);

     int fn_ref_is_link(const FN_ref_t *ref);

     FN_composite_name_t *fn_ref_link_name( const FN_ref_t *link_ref);

     FN_ref_t *fn_ctx_lookup_link(FN_ctx_t *ctx, const FN_composite_name_t *name,
         FN_status_t *status);

     unsigned int fn_status_link_code(const FN_status_t *stat);

     const FN_composite_name_t *fn_status_link_remaining_name(
         const FN_status_t *stat);

     const FN_composite_name_t *fn_status_link_resolved_name(
         const FN_status_t *stat);

     const FN_ref_t *fn_status_link_resolved_ref( const FN_status_t *stat);

     int fn_status_set_link_code(FN_status_t *stat,
         unsigned int code);

     int fn_status_set_link_remaining_name(FN_status_t *stat,
         const FN_composite_name_t *name);

     int fn_status_set_link_resolved_name(FN_status_t *stat,
         const FN_composite_name_t *name);

     int fn_status_set_link_resolved_ref(FN_status_t *stat,
         const FN_ref_t *ref);

     Links are bound to names using the normal  fn_ctx_bind() and
     unbound  using  the  normal   fn_ctx_unbind() operation. The
     operation fn_ref_create_link() is provided for  constructing
     a link reference from a composite name. Since normal resolu-
     tion   always   follows   links,   a   separate   operation,
     fn_ctx_lookup_link() is provided to lookup the link itself.

     In the case that an error occurred while  resolving  an  XFN
     link,  the status object set by the operation contains addi-
     tional information about that error and sets the correspond-
     ing  link  status  fields  using  fn_status_set_link_code(),
     fn_status_set_link_remaining_name(),
     fn_status_set_link_resolved_name()                       and
     fn_status_set_link_resolved_ref(). The  link  status  fields
     can     be     retrieved     using    fn_status_link_code(),
     fn_status_link_remaining_name(),
     fn_status_link_resolved_name()                           and
     fn_status_link_resolved_ref().

ERRORS
     The following status codes are  of  special  relevance  when
     performing operations involving XFN links:

     FN_E_LINK_ERROR
           There was an error encountered resolving an  XFN  link
           encountered  during  resolution  of the supplied name.
           Check the link part of the status object to  determine
           cause of the link error.

     FN_E_LINK_LOOP_LIMIT
           A non-terminating loop (cycle) in the  resolution  can
           arise  due to XFN links encountered during the resolu-
           tion of a composite name.   This code indicates either
           the  definite detection of such a cycle, or that reso-
           lution exceeded an implementation-defined limit on the
           number  of  XFN  links  allowed for a single operation
           invoked by the caller.

     FN_E_MALFORMED_LINK
           A malformed link reference was  encountered.  For  the
           fn_ctx_lookup_link()   operation,  the  name  supplied
           resolved to a reference that was not a link.

APPLICATION USAGE
     For the   fn_ctx_bind(),  fn_ctx_unbind(),  fn_ctx_rename(),
     fn_ctx_lookup_link(),     fn_ctx_create_subcontext()     and
     fn_ctx_destroy_subcontext() operations,  resolution  of  the
     given  name  continues to the target context - that named by
     all but the terminal atomic part of the given name; the ter-
     minal  atomic name is not resolved. Consequently, for opera-
     tions that involve unbinding the terminal atomic  part  such
     as fn_ctx_unbind() , if the terminal atomic name is bound to
     a link, the link is not followed  and  the  link  itself  is
     unbound from the terminal atomic name.

     Many naming systems support a native notion of link that may
     be  used  within  the  naming  system  itself.  XFN does not
     determine whether there is  any  relationship  between  such
     native links and XFN links.

SEE ALSO
     FN_composite_name_t(3XFN),                   FN_ref_t(3XFN),
     FN_status_t(3XFN),                        fn_ctx_bind(3XFN),
     fn_ctx_destroy_subcontext(3XFN),        fn_ctx_lookup(3XFN),
     fn_ctx_lookup_link(3XFN),               fn_ctx_rename(3XFN),
     fn_ctx_unbind(3XFN), xfn_status_codes(3XFN), xfn(3XFN)

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