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I'm currently designing a Java application where a Rule engine could be useful. Where is a good place I can learn about how to use them, how they work, how to implement them, see samples, etc.?
The Drools documentation includes a lot of useful, general purpose information. Especially chapter 2, which covers rule engine basics, knowledge representation, etc. It also includes a nice recommended reading list for coming up to speed on rule engines and expert systems.
For most rule engines, a basic understanding of the rete algorithm usually comes in handy for writing efficient rules. I have personally found the Doorenbos paper referenced in the Wikipedia article to be the clearest technical explanation.
Also, here is a list of open source rule engines in Java.
You might want to read "Should I use a Rules Engine?" from Martin Fowler's blog.
I have worked on a project where we built our own (very simple) rules engine, with the intention to move to a general rule engine when things got too complicated. Never reached that point though, the system has been running happily with the simple homegrown engine for several years now.
I found this site pretty helpful. Are you looking at building your own, or using a 3rd party library?
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I want to know, if there are recommended libraries for decision trees.
For me best laguages atm are Java (easiest) and PHP (long term-usefulness).
I need them for a thesis at university and want to use the code later on as a webservice. The problem itself is not important and could be solved in various ways. But as a condition/constraint I have to use decision trees.
And I searched for quiet a while, but nothing really smashing turned up. So I decided to ask you.
As I said, Java would be easiest for me. And so would be Java-like languages (C++,...). PHP would be most useful as I want to use pieces of that code later on a server. Also frontend programming would be much easier ;-)
Other hosting-supported languages would be ok, too, but I'm not yet familiar with them.
The functionality doesn't need to be very complex as the problem isn't that based on decision trees. It would be nice if I could load the structure (kind of nodes, costs, units) via i.e. XML and than load a configuration-set with dedicated numbers for each node/transistion.
But I'm wondering, if it's maybe easier to implement that stuff myself.
I would be very pleased, if you can recommend something. (And for future investigators other languages wouldn't bother ;-) )
You should look into the Weka API: https://weka.wikispaces.com/Use+WEKA+in+your+Java+code
They have an abundance of decision tree algorithms: ID3, CART, ...
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I'm looking for recommendations for a simple open source implementation of a Distributed Hash Table in Java to play around with. No fancy features, just for learning purposes, no production functionality needed. It should be simple to set up (e.g. 1 physical machine with n-JVMs) and well documented preferably with some examples, tutorials or starting guides.
Research yields these candidates: FreePastry and OpenChord but I'm not fully convinced they meet my criteria simplicity-wise.
Have you got any experience with these or other implementations? Recommendations?
Thanks & adios
There is TomP2P on Github.
Maybe JDHT will fit the bill. I haven't checked it out myself, but it's written at a university, sometimes that means it's simple and used for teaching. :-)
I have been working on an implementation of Kademlia lately. It's very simple to setup and use and it's well documented. There are several tests written that demonstrate the different functionality as well as a starting guide in the Readme.md file itself.
You can use openkad
I started with free pastry..I've had a great experience with it. It was very simple to set up and run a ring of nodes. I've been mainly using PAST (File storage) and its been quite easy to get running. I'd suggest having a look at the PAST tutorial here. https://trac.freepastry.org/wiki/tut_past
The code is over simplified in my opinion but you say that is all you need so I guess thats ok.
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I'm comfing from the .net world, and want a book that goes over the 'right' way of coding.
Things like dependancy injection, loosely coupling of objects, how to layout your web application properly, unit-testing etc.
Google code reviewer's guide, a 38 page pdf which covers writing testable code, loose coupling and dependency injection. The presentations are also highly recommended.
Dependency Injection covers the theory of why you would use dependency injection, in addition to the technical details.
Three books that are language-agnostic, but are considered 'classics':
Desing Patterns (by GoF)
Code complete (by Steve McConnell)
Patterns of Enterprise Application Architecture (by Martin Fowler)
Important: don't read them like belles-lettres - read parts of them while practicing.
While it does not cover some of the things you mention, for me the book to learn Java the right way is definitely Effective Java, Second Edition.
(source: sun.com)
Bruce Eckel's Thinking in Java is a very good introduction into Java for people who already know another language, the PDF version is free for download.
Read a few books if you want, anything "agile", "spring", "TDD" will do, but to be real quick, get a job where they let you work together with a seasoned developer who does pair programming with you... and you will learn more quickly than you can even think about it...
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I saw this post :
https://stackoverflow.com/questions/441198/has-anyone-learned-how-to-program-in-21-days/441224#441224
and I'm not familiar with java APIs, which books do you think will really help me get familiar with those APIs?
Java in a Nutshell, David Flanagan
Java has lots of APIs! Which ones are you interested in becoming familiar with?
What's nice, though, is that Javadocs tend to make APIs easy to learn, by providing method signatures and short descriptions.
Many APIs also have more in-depth tutorials online that you can read. In many cases this can be easier / more accessible / cheaper than buying books.
I would start off with Java Collections, as they are used in most Java applications: http://java.sun.com/docs/books/tutorial/collections/index.html
Note that this is one of Sun's "Trail" tutorials, which are very helpful. Check out the others as well, for those libraries that you are interested in learning. Here is the main index: http://java.sun.com/docs/books/tutorial/index.html
Effective Java by Josh Bloch
You should really start at http://java.sun.com/docs/books/tutorial/index.html
These tutorials are well written, and will get you up to speed quickly. For all the details, go to the documentation at http://java.sun.com/javase/6/docs/api/
If you insist on a book, Thinking in Java by Eckel is not bad, though Eckel can be a bit longwinded and obtuse.
Java Cookbook contains examples to many API's
Then javadoc can be used to adapt to own requirements.
Java 7- complete reference This books not out yet but it might help a lot along with the java docs and all the additional material the others have mentioned.
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I have been looking for an existing open-source syntax-checker for the Object Constraint Language (OCL). I intend to extend the syntax-checker with additional functionality not present in the OCL standard to be more applicable to my usage with entity-relationship diagrams. However, most of the projects I have found are based on the Eclipse Meta-Object Facility (MOF), while I seek only the ability to verify the grammar of an OCL expression (completely independent of any associated class diagrams, etc.). I have begun looking into the source of the Dresden OCL Toolkit (dresden-ocl.sourceforge.net), even though the newest toolkit is also intended for use with the Eclipse MOF. Unfortunately, all downloads are blocked at the company I work for, and it takes 1-2 days minimum to get permission for any download, so I want to know if anyone might be able to point me in the right direction to find what I am looking for.
Thank you very much in advance.
Best regards,
Shona
I've been using Dresden OCL for quite a long time and I think it is a really good starting point for what you want (of course, it is not perfect, last time I checked it still had some problems with recognizing some set operators or navigation expression from association classes).
You can also take a look at the Eclipse OCL plug/in http://www.eclipse.org/modeling/mdt/downloads/?project=ocl
part of the model-development tools initiative
Pointers to other tools supporting OCL (not necessarily open-source) here: http://modeling-languages.com/content/list-ocl-tools
Also, you might by interested in having a look at other tools supporting OCL syntax checking, like Octopus, created(?) by Jos Warmer and Anneke Kleppe, who are authors of the OCL specs.