A name space is hierarchically structured.
A full file name (also called a "full path name" )
has the form
/e1/e2/.../en, as in Unix.
There are a number of Plan 9 services available, each of which provides a tree of files. A name space is built by binding services (or subtrees of services) to names in the name-space-so-far. Typically, a user's home file server is bound to the root of the name space, and other services are bound to conventionally named subdirectories.
Plan 9 has "union directories" : directories made of several directories all bound to the same name. The directories making up a union directory are ordered in a list. When the bindings are made (see bind (1)), flags specify whether a newly bound member goes at the head or the tail of the list or completely replaces the list. To look up a name in a union directory, each member directory is searched in list order until the name is found. A bind flag specifies whether file creation is allowed in a member directory: a file created in the union directory goes in the first member directory in list order that allows creation, if any.
The glue that holds Plan 9 together is a network protocol called 9P , described in section 5 of the manual. All Plan 9 servers read and respond to 9P requests to navigate through a file tree and to perform operations such as reading and writing files within the tree.