blog.quilitz.de

Node.js is an evented javascript I/O framework using Googles V8 JavaScript engine. In the NodeJS wiki there is a good article on how to use Eclipse as Node Applications Debugger. When I tried it, node stoped with segmentation fault as soon as the debugger connected to the process. The fix is easy: set GCC_VERSION=44 before running make during node installation. Viola, it works perfectly.

SVN externals is a really nice feature I used a lot. Switching to git I was really missing it. Of course there is git-submodule but it’s not the same. Now, with version 1.7 git supports so called sparse checkouts which allow you to only include specific sub directories of a repository in your project. You still need to clone the whole repository, but afterwards you can tell git to only show the specified sub directories.

Here is how it works:

1. clone the other repository (in my case, for a Rails app, I did it in vendor/plugins/)

   git clone <repository_url> <directory>

2. cd to <directory>

   cd <directory>

3. enable sparsecheckout

   git config core.sparsecheckout true

4. add directories you want to have in your checkout to .git/info/sparse-checkout, e.g.

   echo app/models/ > .git/info/sparse-checkout
   echo lib/ >> .git/info/sparse-checkout

5. run read-tree

   git read-tree -m -u HEAD

ls now shows

app lib

Forgot a directory you wanted to include? Just repeat step 4 and 5.

There have been several request about DARQ during the past months, so I thought it’s time to post a short project status. DARQ (original website) is a query engine for federated SPARQL queries I worked on in the past. It provides transparent query access to multiple, distributed SPARQL endpoints as if querying a single RDF graph. In other words: It automatically splits an incoming query, sends  sub-queries to the relevant endpoints and merges the results into one resultset. The available endpoints need to be registered in the system using Service Descriptions. This works quiet  well if the vocabularies do not overlap very much, i.e. if two or services store the same properties for resources it can be very slow. However, if there is little overlap query answering can be done in a  reasonable time. Some results of the work were published at ESWC 2008 (paper), the source code is available at sourceforce.

DARQ started as a proof of concept system at HP Labs in 2006, it is in very early stage and I would not recommend to use it in any production environment. I worked on DARQ until early 2008, after that DARQ was continued by a diploma student who added query caching and a basic query translation mechanism, that allows to specify mappings between vocabularies, i.e. “Authors are a subclass of Persons” or “price in EUR can be converted to USD using exchange rare X”. Mappings are defined using SWRL. However, schema mapping support is even more a prototype than DARQ is and has not been tested extensively. He finished his work in Sept. 08, his changes can be found in the svn trunk. The version used for the benchmarks shown in the ESWC 2008 paper is tagged with ‘benchmarks2′ – all documentation writtten by me is for that version. It will likely not work with any of the recent Jena/ARQ releases, though i never tested it. There are currently no plans to continue the development.

If you have any questions related to DARQ feel free to post a comment or email me.

Update: The version in the svn trunk requires a mapping file. This file contains the mapping rules used for query translation. It  must use SWRLs Concrete Syntax representation.

Wow. I finally have a blog. Being involved in a product targeting bloggers (affinityclick.com) I thought it is time to start my own blog (again). Had one ages ago but never wrote that much. It then disappeared during a server crash…. This is a next try.