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+Programming Model
+=================
+
+This document describes the programming model for fission functions.  
+
+See TERMINOLOGY for definitions of terms, such as _function_,
+_instance_, and _trigger_.
+
+
+Idempotency
+===========
+
+Fission assumes that functions are idempotent.  Functions whose instances
+die without a result are restarted, upto a certain restart limit.
+
+
+Time Limits
+===========
+
+By default, there is no time limit on fission functions.  
+
+Idle running instances may be killed at any time (usually after the
+default idle timeout of 10 minutes, but this is configurable).
+
+
+Mapping
+=======
+
+This section specifies the mapping between: (1) HTTP and other
+triggers, and (2) function parameters, return values, and exceptions.
+
+In other words, this section describes how a function should be called
+based on a given trigger, and how the functions behaviour affects the
+result returned from the trigger.
+
+The HTTP Trigger
+----------------
+
+NodeJS
+------
+
+NodeJS functions are called with a context object.
+
+context.request contains the nodeJS Request object.
+
+In addition,
+
+context.queryString contains the parsed querystring
+
+context.body contains the parsed body
+
+context.status sets the HTTP response status code.  If context.status
+is an invalid HTTP status, then the HTTP status is set to 500.
+
+Exceptions result in a HTTP 500 error.
+
+
+
+
+
+XXX Should we have a "context.done()"?  What are the pros and cons?
+
+XXX Who handles serialization and deserialization?  Should we do json
+    automatically based on content-type and accept headers?
+
+
+Python
+------
+
+Same as node, pretty much.
+