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django-stockandflow 0.0.4

Django stock and flow tracking for business intelligence metrics

==================
django-stockandflow
==================

Django stock and flow tracking for business intelligence

Installation
============

1. Install from PyPI with ``pip``::

    pip install django-stockandflow

.. _in-development version: https://github.com/jesseh/django-stockandflow.git

2. Add ``stockandflow`` to ``INSTALLED_APPS`` setting.

3. Create a cron job to call ``./manage.py run_periodic_schedule`` at an
   interval that is at least as frequent as your most frequent period that you
   register with the periodic scheduler. Hourly, or perhaps every 10 minutes,
   is likely to be sufficient.

4. Start creating stocks and flows.

Dependencies
------------

- ``Django >= 1.2`` (not yet tested with 1.3)

.. _Django: http://www.djangoproject.com/

Introduction
============

Django Stock and Flow is a business intelligence tool. The goal is to transform
the raw data in a Django application into views that answer business questions.
Just as the Django Admin interface makes it easy to manage data in your
project, Django Stock and Flow makes it easy to define, track and present
business metrics for your project.

The theory behind Django Stock and Flow is based on `system dynamics`_. There
is more information on the concept of stocks and flows on wikipedia_.

In addition to tracking metrics, Django Stock and Flow has hooks for running
automation code when flow events occur and when the stocks are counted. These
hooks are useful, for example, to create decaying stocks. The system can
automatically transition an object through a set of states, like 'hot', 'warm'
and 'cold' over time.

**This app is very much in development.** The api is likely to change in ways
that are not backwards compatible.

.. _`system dynamics`: http://en.wikipedia.org/wiki/System_dynamics
.. _wikipedia: http://en.wikipedia.org/wiki/Stock_and_flow

Key Concepts
============

Stock
-----
An accumulation defined by a queryset.

In the abstract a stock is a collection that is counted at a specific time
interval, generating a StockRecord). The state of an object defines it's
membership in a given stock. As a result, the words state and stock are roughly
interchangeable.

In the specific a stock is a subset of records for a given model that meet the
conditions defined in the queryset.

For example a User may have an "active" stock and an "inactive" stock defined
by whether or not each user.is_active == True.

There is no model associated with a stock.

Facets is a list of either facet objects or tuples of the form (facet,
field_prefix). The field prefix maps the object of the stock to the object that
is filtered in the facet. For example, if there is a User with a Profile and a
facet on the Profile object like "yada"="true" then a User stock would use the
field_prefix "profile" so that the field lookup in the facet becomes
"profile__yada"=True.


Flow
----
A named relationship between stocks representing the transition of an object
from a source stock to a sink stock. A flow enables the transitions to measured
over an interval of time to track the rate of occurence.

A flow may have any number of source or sinks stocks. None is a valid source or
sink that represents an external, or untracked stock. Any other class, such as
an int or a string can be used a stock stand-in for creating flow events
between states that do not have an associated Stock instance.

Continuing the example in the Stock docstring, when a new user is created the
flow from None to the stock "active". A flow to track this tranisition could be
called "activating".  The activating flow would also have "inactive" as a
source to handle the case where a previously inactive user becomes active
again.

The optional event_callables list is called whenever an flow event is created
for this flow. It receives the flowed_obj, source and sink. An example use
would be to send an email each time an activating flow occurs.


Facet
-----
A facet is used to split a stock or flow into sub-queries. For example, one
could track users, and then add a facet based on is_active to track how many
are active vs. inactive.

 - The name is used to refer to the facet.
 - The field lookup is the same as the left side of a kwarg in a filter
   function.
 - Values can either be a list or a ValuesQuerySet with flat=True. If it is a
   ValuesQuerySet then it will be re-evaluated at every use.


Flow Event
----------
An abstract base class for the timestamped event of an object moving from one
stock to another.

Each type of object that flows needs to have an subclass of the FlowEvent model
to capture events on objects of that class. This approach avoids using a
generic foreign key and the limitations that come with it.

Flow events combine to create a  flow variable that is measured over an
interval of time. Therefore a flow would be measured per unit of time (say a
year).

Subclasses must have a "subject" foreign key field.


Stock Record and Stock Facet Record
------------
A record of the count of a given stock and its facets at a point in time. There
is one model to capture the stock records for all the stocks.


Flow Record and Flow Facet Record
------------
*To be implemnted*

A record of the time-framed count of flow events for a given flow and its
facets. There is one model to capture the flow event records for all the flows.


Model Tracker
-------------
A common use case is to generate flow events when data in a given model
changes. This class does the heavy lifting to make that happen.

It generates flow events by monitoring for changes to the fields_to_track
list, runs the old and new field values through the states_to_stocks_func
function to figure out the source and sink stocks. Then it tries to checks
if any of the flows will make an event for that transition.

The states_to_stocks_func receives two tuples of field values in the order that
they are declared in fields_to_track. The first tuple lists the previous value of the
fields and the second tuple lists the current value of the fields. The function must
return a pair of tuples of stocks (they can be a 1-tuple). This allows a single model's
state be composed of any number of sub-states/stocks. The resulting previous
and current state tuples are then compared element by element.

Thanks to carljm for the monitor in django-model-utils on which the
change tracking is based.


Periodic Scheduler
------------------
Periodically call a set of registered callable functions.

This can be used, for example, to periodically count a stock and generate stock
records. It could also be used to periodically decay objects from one stock to
another.

The periodic scheduler requires that a cron job call the management command
``run_periodic_schedule`` at regular intervals. The system sorts out which
registered function to run at each invocation.


Process
-------

A view helper class to group stocks for use in a view. Any set of stocks, flows
and associated facets can be added to a Process. Passing the Process object to
a template is an easy way to provide all of the data required for a given set
of metrics.

*The Process class is only a skeleton implementation. In the future it should
include helpers and possibly templates to rapdily report on stocks and flows.*


Stock and Flow Admin
--------------------
This leverages Django's fantastic built-in admin to offer great functionality
for both stocks and flows. Via this interface the stocks and flows can be
viewed and actions applied.

The StockAndFlowAdminSite registers a proxy model for each stock and flow to
get around the fact that the admin site does not like a given model to be
registered more than once.

This stock and flow admin is meant to be registered as a seperate admin site so
that it does not clutter up the normal admin with dynamically created stock and
flow entries.


Usage
=====
See the ``example`` folder. This code is meant to be an example. **It will not
execute.**


For Help
========
Django Stock and Flow is very much in development and the documentation could
use some work.  If you want help implementing this please contact me at
jesseh@i-iterate.com.

CHANGES
=======

tip (unreleased)
----------------

0.0.1 (2011.06.30)
------------------
- Initial release

0.0.2-4 (2011.12.3)
------------------
- Fixed pip install process.
TODO
====

- Create FlowRecords.
- Enhance views to generate generic stock and flow reports for a process.
- Test with Django 1.3.
 
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