ShapeLogic for general declarative programming

ShapeLogic 0.9 is going to be the first release where users define rule sets read from either databases or flat files. I have decided to broaden the scope of the project.

First I hoped that I would be able to make minor adjustment to ShapeLogic's letter match example so that it would read the rules from an external source and gradually expand. But since backward compatibility is not a problem yet, I came to the conclusion that it was better to try to construct a solid foundation for declarative programming. While it will be primarily geared toward computer vision problem solving, the system will have other, broader, applications as well.

Do we need another system for declarative programming?

SQL rules supreme in the field of simple data, but once you go outside this field there are many different directions that you can take.

The declarative logic programming system that I had highest expectations for was CYC. It is a large, hand coded knowledge base trying to capture common sense, using many different inference techniques. Strangely, it never got a big following even after they released part of the engine as open source.

I hope to find a sweet spot where a simple system will be able to do some real work and be simple to learn. My work is geared toward a domain where there are a limited number of objects with somewhat constant features.

A few of the changes in ShapeLogic 0.9

Lazy data streams

Implement lazy data streams like Scala or Scheme.

Decouple annotation

Make the annotation of shapes more loosely coupled to classes in ShapeLogic. I was not super happy with the first solution that I came up with of how to annotate point, lines and polygon.
If ShapeLogic should be used for more general problem this is completely unacceptable.

Better interpreter

I order to save user defined rule in a database or a flat file, I need to be able to compile or interpret this code. This code in the rules should mainly be fairly straightforward.

The top contenders are:

• Java 6 Scripting interface, that should give access to different scripting languages for the JDK


• Java 6 Compiler interface, the problem is that Java is pretty verbose


• Groovy intepreter


• Do the parsing in ShapeLogic and write a little interpreter


• Stick with JEXL for now, and make the move in a later release

-Sami Badawi

Declarative and Object Oriented programming

One of the main objectives for ShapeLogic is to make a good hybrid of Declarative programming and Object Oriented programming. This is not specific to computer vision, but is a general problem. This is a daunting task, and many people have tried and the state of the art still leaves a lot to be desired.

I have started to work on the first release of ShapeLogic with an external rule based engine, I have not worked through all the problems yet. I think that this is a case of evolutionary programming where you have to try out and approach, not knowing if it will lead to anything useful. Hopefully I will have ShapeLogic 0.9 ready pretty soon.

I think that the key is to keep it simple and keep the syntax easy to work with. Let me just give my 2 cents on a few project that combined Declarative programming and Object Oriented programming.

Approaches that impressed me

Prova is a Java Prolog hybrid. I was very impressed by the simplicity and how well it managed to integrate queries with normal database access. Unfortunately I do not think that Prolog is applicable to the approach to computer vision, that I am pursuing in ShapeLogic now.

List Comprehension in Python and Haskell. It is somewhat limited, but it is very convenient to work with.

Microsoft LINQ, I think that it is great that you can use the same simple syntax to query databases, XML and collections.

Hibernate and ORM tools: While I do not think that the dust has settled yet as to how feasible they are for production system with large databases. I think they are very promising. This was the reason that I included Hibernate in ShapeLogic, despite it not being used much yet.

Promising approaches that I found hard to work with

Drools: An open source RETE engine for the Java JVM. It comes with a lot of cool features, but I thought that the example program setting a rule up to calculate Fibonacci numbers was too complicated.

OWL: Works with XML / RDF. It is a standard. It comes with good open source tools, but it just seems too heavy weight for my purpose.

-Sami Badawi