Updated docs.

docs/developers/model.md

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+# Object Model
+
+This document describes the different objects we store and the relationships between them.
+
+## Applications
+
+At the root of everything are applications. In `fn`, an application is essentially a grouping of functions
+with path mappings (routes) to each function. For instance, consider the following URLs for the app called `myapp`:
+
+```
+http://myapp.com/hello
+http://myapp.com/users
+```
+
+This is an app with 2 routes:
+
+1. A mapping of the path `/hello` to a function called `hello`
+1. A mapping of the path `/users` to a function called `users`
+
+## Routes
+
+An app consists of 1 or more routes. A route stores the mapping between URL paths and functions (ie: container iamges).
+
+## Calls
+
+A call represents an invocation of a function. Every request for a URL as defined in the routes, a call is created.
+The `call_id` for each request will show up in all logs and the status of the call, as well as the logs, can be retrieved using the `call_id`.
+
+## Logs
+
+Logs are stored for each `call` that is made and can be retrieved with the `call_id`.