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Active Modules / Active Objects

• Modules to which computational resources are attached.
• High-level model of client-server interaction.
• An active module is a network-wide server for the predicates it exports.
• Any module or application can be converted into an ``active module'' (active object) by using a special form of save:
  :- save_active_module(Filename, Addr, Report_Addr).
  (Report_Addr is code to report Addr)
• Procedures can be imported from remote ``active modules'' via a simple declaration: E.g.
  :- use_active_module(Name, [P/N, P/N,...]).
• A hook predicate to locate active modules (configurable): module_address(Name, Addr)
• Calls to such imported procedures are executed remotely in a transparent way.
• Example application: client-server. Client imports module which exports the functionality provided by server. Access is transparent from then on.
• Typical examples of active objects: databases, name servers, agendas, WWW form handlers, WWW cgi-bin servers, demons (ftp, telnet, ...), etc.
• Implementation: built as an abstraction on top of ports/sockets (can also be easily built on top of a blackboard).