#lang scribble/manual
@require[racket/include]
@include{prelude.inc}

@title{Concepts}

Marketplace integrates ideas from both distributed systems and
virtualized operating system designs to obtain an architecture of
nested @emph{virtual machines}. Each nested layer is equipped with its
own publish/subscribe network that also propagates @emph{presence}
information about the (dis)appearance of services.

The result suggests a @emph{marketplace} metaphor, where communicating
programs exist in a noisy, crowded, even chaotic context, rather than
in a quiet place systematically going through their inboxes.

@section{What is a process, what are event handlers?}

@deftech[#:key "process"]{Processes} are ...

@deftech{Process State} is ...

@deftech{Events} ...

@deftech{Actions} ...

@section{What is a VM?}

@deftech[#:key "vm"]{Virtual Machines (VMs)} are ...

@section{Endpoints: Subscription and Advertisement}

The Marketplace operating system's inter-process communication
facility is structured around @deftech[#:key
"pub/sub"]{publish/subscribe (pub/sub)} messaging.@note{For a survey
of pub/sub messaging, see
@hyperlink["http://www.cs.ru.nl/~pieter/oss/manyfaces.pdf"]{"The Many
Faces of Publish/Subscribe"}, ACM Computing Surveys, Vol. 35, No. 2,
June 2003, pp. 114–131. There's also plenty out there on the Internet;
a good starting point is to google for
@hyperlink["https://www.google.com/search?q=pub/sub message-oriented middleware"]{pub/sub message-oriented middleware}.}

@deftech{Endpoints} are ...

A @deftech{role} describes the role some process is playing in a
conversation. Concretely, roles are represented by @racket[Role]
structures. A role can be used by the currently-running process to
describe some role it wishes to play, or can be carried in some
@racket[EndpointEvent] to describe the role some @emph{peer} process
is playing in a conversation.

Roles have three parts:

@itemlist[

  @item{An @deftech{orientation} (type @racket[Orientation]) describes
  whether this role is concerned primarily with @emph{producing} or
  @emph{consuming} messages.}

  @item{A @deftech{topic} is a @deftech{pattern} over messages. Topics
  perform double duty: they both scope conversations and filter
  incoming messages. More on topics below.}

  @item{An @deftech{interest-type} (type @racket[InterestType])
  determines whether the endpoint playing the given role is genuinely
  a participant in matching conversations or is simply observing the
  real participants. More on interest-types below.}

]

@deftech{Messages} are ...

@subsection{Topics}

As mentioned above, topics ...

@subsection{Interest Types}

...

@section{Presence}
@section{Nesting, relaying, and levels of discourse}