Source: Semantic Web world for you

A few days ago, I posted about SemanticXO and how you will see how to install a TripleStore on your XO. Here are the steps to follow to compile&install RedStore on the XO, put some triples in it and issue some queries. The following has been tested with an XO-1 running the software 10.1.3 and a MacBookPro running ArchLinux x64 (it’s not so easy to compile directly on the XO, that’s why you will need a secondary machine). All the scripts are available here.

Installation of RedStore

RedStore depends on some external libraries that are not yet packaged for Fedora11, which is used as a base for the operating system of the XO. The script build_restore.sh will download and compile all the necessary stuff. You may however need to install external dependencies on your system, such as libxml. That script only takes care of the things redstore directly depends on, namely raptor2, rasqal and redland (all available here). Here is the full list of commands to issue:

mkdir /tmp/xo
cd /tmp/xo
wget --no-check-certificate https://github.com/cgueret/SemanticXO/raw/master/build_redstore.sh
sh build_restore.sh

Once done, you will get four files to copy on the XO and if you don’t, you can also download this pre-compiled package. These files shall be put all together somewhere, for instance “/opt/redstore”. Note that all the data redstore needs will be put into that same directory. In plus of these 4 files, you’ll need a wrapper script and an init scripts. Both are available on the source code repository. So, here what to do on the XO, as root (replacing “cgueret@192.168.1.105″ by the login/IP accurate for you) :

mkdir /opt/redstore
scp cgueret@192.168.1.105:/tmp/xo/libraptor2.so.0 .
scp cgueret@192.168.1.105:/tmp/xo/librasqal.so.2 .
scp cgueret@192.168.1.105:/tmp/xo/librdf.so.0 .
scp cgueret@192.168.1.105:/tmp/xo/restored .
wget --no-check-certificate https://github.com/cgueret/SemanticXO/raw/master/wrapper.sh
chmod +x wrapper.sh
cd /etc/init.d
wget --no-check-certificate https://github.com/cgueret/SemanticXO/raw/master/redstoredaemon
chmod +x redstoredaemon
chkconfig --add redstoredaemon

Then you can reboot your XO and enjoy the triplestore through its http frontend, available on the port 8080

Loading some triples

Now that the triple store is running, it’s time to add some triples. The SP2Bench benchmark comes with a tool (sp2b_gen) to generate any number of triples. To begin with, you can generate 50000 triples. That should be about of the maximum amount of triples an XO will have to deal with later on when the activities will store data in it. Here is what to do, with “192.168.1.104″ being the IP of the XO:

sp2b_gen -t 50000
rapper -i guess -o rdfxml sp2b.n3 > sp2b.rdf
curl -T sp2b.rdf 'http://192.168.1.104:8080/data/http://example.com/data'

It takes about 43 minutes to upload these 50k triples which gives an average of 53 milliseconds per triple or 19 triples per second. That’s not fast but should be enough to have an API allowing to store a bunch triples with an acceptable response time. The data takes 4Mo of disk space on the XO for an initial RDF file of about 9.8Mo.

Issue some queries

The SP2Bench benchmark comes with a generator for the triples and a set of 17 SPARQL queries expressed over this data. The queries are of changing complexity in order to benchmark different triple stores. Unfortunately, 9 of them where to complex for RedStore on the XO, with these 50k triples. These queries where not solved, even after being executed over a full night! The 8 remaining queries are solved without much problems, as long as you have enough time to wait for the answer:

The queries have been executed using the “sparql-query” command line client that way:

cat q2.sparql | sparql-query http://192.168.1.104:8080/sparql -t -p -n

The long delay can sounds as a bad news but it must be noted that this was with 50k triples and with queries designed to be tricky in order to test triple store capabilities. Considering a normal usage with fewer triples and more standard queries, we can expect things to go better.

Source: Semantic Web world for you

The three XOs received for the project

The project One Laptop Per Child (OLPC) has provided millions of kids world wide with a low-cost connected laptop helping them to enhance their knowledge and develop learning skills. Learning a foreign language, getting an introduction to reading/writting or preserving/revive an endangered/extinct language are among the possible usages of these XOs. Such activities could take a significant benefit from a storage layer optimised for multi-lingual and loosely structured data.

One of the building block of the Semantic Web, the “Triple Store”, is such a data storage service.  A triple store is like a database engine optimised to store and provide access to triples, atomic statements binding together a subject a predicate and an object. For instance, <Amsterdam,isLocatedIn,Netherlands>. And these two triples would define two different names for two different languages: <Amsterdam,isLocatedIn,”Netherlands”@nl>,  <Amsterdam,isLocatedIn,”Pays-Bas”@fr>.

SemanticXO is a new project from the contributor program aimed at adding a triple store and a front-end API on the XOs’ operating system. This triple store will extend the functionalities of Sugar with the possibility for all activities to store loosely structured/multilingual data and easily connect information across activities. In plus, the SPARQL protocol will allow for an easy access to the data stored on any device.

A first goal is to setup RedStore on the XOs allocated to this project. RedStore is a lightweight triple store that should be able to run on low hardware and still provide nice performances. Stay tuned for the result!

Source: Semantic Web world for you

This is the first post on this blog, aimed at giving and pointing to information about the Semantic Web. The Semantic Web (or Web 3.0) is a new technology and research topic aimed at putting more semantic into the Web as we know it. The changes are happening, in a not so visible but very concrete way for you, user of the Web. On this blog you will learn more about it and how you can benefit from it, whoever you are.