URLdescriptor strings are of the form:

  casa:// [ user @ ] host [ : port ] [ / [ [   dir  / ]* [ file ] ] [# key [ = value ] [ & key [ = value ] ]* ] ]
                                           --directory--            -------------------data--------------------
                                           --------path----------

where

user is an alphanumeric local identifier for an individual user.
host is an IP address or host name.
port is a numeric value.
path specifies a domain-specific description of an agent type.
directory is the part of of the path. Usually, this represents the type of the agent.
dir is an alphanumeric string.
file is an alphanumeric string that is part of a path. Usually, this represents the name if the instance of the agent.
data specifies various data elements that might be used by the agent.
key is a key string (case sensitive) to retrieve the associated value.
value is an alphanumeric string.

There are two directly supported key/value pairs:

lac=port is the port number of the agent's LAC. Note that the host of the LAC and the agent itself must be identical.
indirect=booean specifies whether messages need to be sent through the agent's LAC (true means send through the LAC, false means send directly). This is usually used when traversing a firewall, where the LAC port is left open, but the other ports may be blocked. If the IP address is local (the subnet is the same), then this setting is ignored.

for example:

agent12@www.cpsc.ucalgary.ca:8000 describes an agent called agent12 that is currently running and listening at port 8000

136.159.2.4/canada/alberta/calgary#lac=9000&indirect=true describes an agent instance ("calgary") of type "canada/alberta" that may or may not be running on an unknown port, but it can be started or its port number obtained from the LAC running on port 9000 and communication to that agent should be indirectly though it's LAC (the first item in the receiver list should be the LAC [who's address is 136.159.2.4:9000]).

URL strings are of two types:

resolved where the current port of the agent is known. In this case, the path is usually ignored by the system.
unresolved where the current port of the agent is not known, but the url may become resolved if the the path and lac ("#lac=") are known. This resolution may be done by sending a resolve request message to the LAC (which must have the same host as the agent), asking it to resolve the URL. If the agent is running, the LAC may simply return a resolved URL. If the agent is not currently running, the LAC may activate and run the agent on some port, then return the a resolved URL.

URLs are supported in the software by the class URLDescriptor.

Copyright: Copyright (c) 2002, Knowledge Science Group, University of Calgary. Permission to use, copy, modify, distribute and sell this software and its documentation for any purpose is hereby granted without fee, provided that the above copyright notice appear in all copies and that both that copyright notice and this permission notice appear in supporting documentation. The Knowledge Science Group makes no representations about the suitability of this software for any purpose. It is provided "as is" without express or implied warranty.