Semantic Web Company

Days 3 and 4 of the OntoWiki KickOff Meeting in Leipzig were comprised of semantic technologies and OntoWiki development workshops.

Just like the overall organization of the project meeting was very good, so Sebastian Dietzold, Sebastian Hellmann, Michael Martin and Jörg Unbehauen did a real good job at putting the ideas behind key concepts of the semantic web across in several introductory SemWeb presentations. Their talks about various technologies from the semantic web stack like URIs, RDF and its serialisations, RDFS, SPARQL and some related tools were well suited to bring people who are relatively new to the semantic web up to speed. Links to the presentation slides can be found at the project page in the coming days.

Later Jens Lehmann outlined the new things OWL 2 brings, e. g. profiles, which are subsets of OWL 2 and which provide different degrees of expressivity and reasoning efficiency.

The last day started with Sören Auer’s presentation of their semantic wiki OpenResearch, a site where information on conferences, journals and scientists is pooled. OpenResearch is built with Semantic MediaWiki (SMW), just like our Social Semantic Web wiki.

While SMW is a very useful tool as it lowers the entry barriers for using semantic wikis, Sören also pointed out  that in comparison OntoWiki provides some important features that SMW doesn’t have:

• SMW doesn’t use SPARQL for its queries, but a less powerful custom query language, whereas OntoWiki has full SPARQL support.
• OntoWiki’s UI has many widgets that support the user when entering data or new properties on a page (e. g. there is an autocomplete feature for suggesting properties)
• With SMW changes to the wiki’s semantic structure often entail manual changes to many, many pages. With OntoWiki it is easy to e.g. change poperties at any time.

For the new version of OntoWiki Sören and his team use the Zend framework and develop the Erfurt API to store and access RDF data. The Erfurt API supports SPARQL, versioning, caching and RDF based authentification/access control. It abstracts different stores using the adapter pattern, so it can be used with Virtuoso and any other store which has an interface provided by Zend_Db (MySQL, Oracle, PostgreSQL, etc.) plus they are working on an interface for Redland. Find the slides for Philipp Frischmuth’s Erfurt API presentation here, the API documentation here and Norman Heino’s Zend & OntoWiki Application Framework presentation here.

Julian Jöris demonstrated how Selenium is used for acceptance testing. This is a very promising testing framework for web applications, where one can e.g. record interactions with different browsers and automatically run them as tests. Selenium has a Firefox extension to record macros and is integrated with PHPUnit.

Finally we had a very good discussion about our conX-OntoWiki integration use case and application ideas, so we left Leipzig with a pleasant anticipation of the coming co-operation in the project.

The third session at WOD-PD was dedicated to “Bringing (Legacy) Data on the Web“, and led by Sören Auer (University of Leipzig, Germany) and Orri Erling (OpenLink Software) .

Sören Auer described the difference between the Web 1.0, 2.0 and 3.0 as follows: On the Web 1.0, you had many websites that provided unstructured, mainly textual content. On the Web 2.0, you have a few large websites that are specialised on specific content types. And, finally, on the Web 3.0, there are many websites which contain, and are able to semantically syndicate, arbitrarily structured content.

So why would we need another web? What you cannot do with the current web is finding answers to seemingly complex, yet in reality pretty mundane question such as: Where in Leipzig do I find an apartment that is close to bilingual, German-French child care facilities? Are there any ERP service providers which have offices in Vienna and Berlin? Who are the researchers in South-East Asia currently working on database related topics?

Sören further discussed three of the present means of bringing relation data to the web: Triplify (a web application plugin that exposes data from relational databases in RDF), D2RQ (a declarative language to describe mappings between relational database schemata and OWL/RDFS ontologies, developed at Free University Berlin), and Virtuoso Universal Server (a middleware and database engine hybrid delivering for instance data integration for SQL, RDF, XML, Web Services). With respect to Triplify, Sören – who is Triplify’s founder and main developer at AKSW Uni Leipzig – showed and discussed the configuration for Wordpress 2.1., which can be found here (click here for more configurations, e.g. for Joomla, OpenConf and Drupal). The next aim for Triplify is to become an integral part in enduser web app distibutions.

And important question raised by Sören was: How do next generation search engines know that something has changed on the web of data? He suggested three approaches:

1. Always try to crawl everything (this may sound silly – but that’s actually what is happening on the current web)
2. Ping a central update notification service – e.g. PingTheSemanticWeb.com – which works as a showcase, but will probably not scale if the data web gets really deployed.
3. Each linked data endpoint publishes an update log – e.g. with Triplify, as a special folder inside the Triplify namespace, e.g. http://example.com/Triplify/update

Also discussed by Sören and worth checking out is Reuters’ Semantic proxy – the demo went live in late September.

Orri Erling, as the lead developer of the Virtuoso Team, addressed the issue of mapping relational databases to RDF with OpenLink Virtuoso. In his talk, he addressed the pros and cons of RDF data warehouse:

Pros

• Even query performance across all data
• Possibility of forward-chaining inference
• Some SPARQL features may be better supported, e.g. Unspecified predicates

Cons

• Keeping data up-to-date
• Complex set up, needs dedicated servers: you don’t build them on a whim

What Virtuoso delivers is mapping of SPARQL to SQL against any existing schema (whether stored in Virtuoso or elsewhere); a physical quad-store (quad as in quadruple; not as in quad-bike ; and Federated/local Relational Data Base Management Systems (RDBMS).

A more detailed discussion of the requirements for Relational-to-RDF Mapping is available on Orri’s blog, where he discusses it in the light of his own experience. A power point presentation of a previous talk he gave to the W3C RDB2RDF Incubator Group can be downloaded here: Mapping Relational Databases to RDF with OpenLink Virtuoso (PPT, 115KB). His summary of the group discussions around the same topic, Requirements for Relational to RDF Mapping, can be found here.

Orri also showed the Virtuoso billion triples demo which, according to the corresponding blogpost, “is being worked on at the time of submission and may be shown online by appointment.” The demo was a submission to the Billion Triples Challenge.

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• Linking Open Data Triplification Challenge at I-Semantics 2008
• Virtuoso Universal Server