The syntax allows for the inclusion of a user name and even a password for those systems which do not use the anonymous FTP convention. The default, however, if no user or password is supplied, will be to use that convention, viz. that the user name is "anonymous" and the password the user's internet-style mail address.
The FTP protocol allows for a sequence of CWD commands (change working directory prior to a RETR which actually accesses a file. The arguments of any CD commands are successive segment parts of the URL, and the filename argument to the RETR command is the final segment of the URL path.
There is no common hierarchical model to the FTP protocol, so if a directory change command has been given, it is impossible in general to deduce what sequence should be given to navigate to another directory for a second retrieval, if the paths are different. The only reliable algorithm is to disconnect and reestablish the control connection. However, if no directory changes have been made, but direct retrieval has been done, then the control
(This note previously read: "The adoption of a unix-style syntax involves the conversion into non-unix local forms by either the client or server. Some non-unix servers do this, but clients wishing to access sites which do not have unix-style naming will need certain algorithms to enable other file systems to be identified and treated. Client software may also have to be flexible in terms of the sequence of FTP commands used with different varieties of server. In view of a tendency for file systems to look increasingly similar, it was felt that the URL convention should not be weighed down by extra mechanisms for identifying these cases." )