Machine Learning (Theory)

10/22/2006

Exemplar programming

Tags: Language,Machine Learning jl@ 8:59 pm

There are many different abstractions for problem definition and solution. Here are a few examples:

  1. Functional programming: a set of functions are defined. The composed execution of these functions yields the solution.
  2. Linear programming: a set of constraints and a linear objective function are defined. An LP solver finds the constrained optimum.
  3. Quadratic programming: Like linear programming, but the language is a little more flexible (and the solution slower).
  4. Convex programming: like quadratic programming, but the language is more flexible (and the solutions even slower).
  5. Dynamic programming: a recursive definition of the problem is defined and then solved efficiently via caching tricks.
  6. SAT programming: A problem is specified as a satisfiability involving a conjunction of a disjunction of boolean variables. A general engine attempts to find a good satisfying assignment. For example Kautz’s blackbox planner.

These abstractions have different tradeoffs between ease of use, generality, and the effectiveness of existing solutions.

Machine learning can be thought of as exemplar programming. Exemplar programming is creating examples of a (input,output) pairs which are used by an algorithm to predict a function from input to output. Basic questions about this abstraction are:

  1. How easy to use is it? An honest answer here is “not very”. There are several subtle issues related to overfitting, independence, and representativeness of the samples which take significant effort to describe to an unfamiliar person. Making this abstraction easier to use via careful language design is an area where effort may pay off.
  2. How effectve are the exemplar programming solvers (aka learning algorithms)? There is huge variance with respect to the problem under consideration. For some problems, some learning algorithm is very effective while for others you might as well have not tried.
  3. How general is exemplar programming? Very general. A great many problems can be phrased as “given this, I want that”.
  4. How effective has examplar programming been? Increasingly effective.

Exemplar programming is a viewpoint of machine learning which (mostly) ignores statistics, prior information, and the possibility of overfitting. That’s a great deal to ignore, but there are gains as well.

  1. Exemplar programming creates a split between problem solution and problem formation. This is important because the problem solver can heavily optimized (for speed, scalibility, effectiveness on common problems, etc…) making the process of apply machine learning simply a matter of specifying the exemplars.
  2. The formation/solution split helps us focus on problem formation independent of solution. The big gains in machine learning in the last decade seem to be discovering how to apply to new areas. A significant step in any application to a new area is discovering the right way to formulate the problem.

Exemplar programming seems to be a useful viewpoint for machine learning in “big data” problems with many examples where significant prior information is lacking. When either of these conditions are not met, other viewpoints/approaches to machine learning may be more succesful.

3 Comments to “Exemplar programming”
  1. Bianca says:

    When I try to explain machine learning to people outside the field I usually start with an “exemplar programming” argument: “imagine you want to write a program for some task, but it is too hard to code it manually AND you have examples of (input,output) pairs, such as in spam detection or character recognition. In this case, you can apply machine learning to ‘learn’ a program for the task”. At least as a motivation mechanism, I find this viewpoint effective, since any programmer can relate to it.

  2. Drew Bagnell says:

    I think exmplar programming does capture a lot of people’s natural idea about machine learning. But I think it needs a bit of modification to capture, for instance, reinforcement learning. John?

  3. SoloGen says:

    To Drew: When I want to describe reinforcement learning to an outsider (being an engineer, a social scientist, and etc.), I describe it as a hypothetical robot that wants to learn something by getting reward/punishment in a way similar a human do.

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