Posts tagged Semantic Web
Hybrid Ontology + Relational Store with SQL Server
May 25th
There are many references in the literature to exposing existing SQL data sources as RDF. This is certainly one way to integrate existing databases with semantic reasoning tools but it clearly requires a lot more storage and processing than simply keeping the data in SQL and querying over it directly. So recently I began some experiments to create a hybrid store by merging an ontology triple (quad) store with an existing database. By linking each row in other SQL tables to an Entity in the triple store I can take advantage of their existing columns, indexes, relationships etc. whilst also being able to reason over them. The first part of this is now working, Entities can be derived types stored in separate SQL tables linked only by an Id, and I am now moving on to getting the metadata in place that will provide all of the implied relationships that can be derived from an existing row-structured database into the ontology store – not as duplicated information but as a service that the reasoner will use to get statements about the SQL content. Clearly this will require changes in both the reasoner and the store but I think the net effect will be a much more efficient reasoner able to reason over large volumes of structured information quickly without having to first turn everything into a statement triple.
An ontology triple (quad) store for RDF/OWL using Entity Framework 4
May 12th
This weeks side-project was the creation of an ontology store using Entity Framework 4. An ontology store stores axioms consisting of Subject, Predicate, Object which are usually serialized as RDF, OWL, N3, … Whereas there’s lots of details about these serialization formats, the actual mechanics of how to store and manipulate them was somewhat harder to come by. Nevertheless, after much experimentation I came up with an Entity Model that can store Quads (Subject, Predicate, Object and Meta) or Quins (Subject, Predicate, Object, Meta, Graph). The addition of Meta allows one Axiom to reference another. The addition of Graph allows the store to be segmented making it easy to import some N3 or RDF into a graph, then flush that graph if it is no longer needed or if a newer version becomes available.
The store is currently hooked up to an Euler reasoner that can reason against it, lazily fetching just the necessary records from the SQL database that backs the Entity Model.
Here’s the EDMX showing how I modeled the Ontology Store:
Applying the Semantic Web to Home Automation
Apr 26th
Recently I’ve been considering how the Semantic Web will impact home automation.
Technologies like the Web Ontology Language (OWL) and RDF allow for the construction of complex ontologies that define what things are, and how they relate. Using these ontologies automated reasoning can be applied to generate new facts or to prove or disprove assertions.
This sounds like the ideal companion to the Natural Language Processing (NLP) Engine that I have already created for the my home automation system. With reasoning powers added to the natural language engine and the ability to augment the knowledge base by adding new assertions the whole system will be much more powerful. One day it might even be possible to create the entire home definition using a natural language text file and to query the system using rich natural language queries.
So, the first step is to find an existing ontology store and reasoning engine. A quick web search reveals that most are built in Java. There were a couple of links I came across later for .NET: http://razor.occams.info/code/semweb/ and http://www.intellidimension.com/products/semantics-server/. There’s also an interesting Q&A site at http://semanticoverflow.com which has lots of useful information on it.
But rather than starting with some existing library I really wanted to understand more deeply how an ontology store works and how a reasoning engine functions, so over the course of a couple of evenings I created my own. I now have a triple store and a simple reasoning engine. Here’s an actual conversation so you can see what it’s capable of so far and can perhaps get a glimpse at how powerful this concept could be:-
house is a class
contains is a property
contain is a property
contains is the same as contain
contain is the same as contains
contains is transitive
contain is transitive
first floor is a class
room is a class
kitchen is a room
first floor contains kitchen
house contains first floor
does house contain kitchenHouse: Yes, house contain kitchen because [house contains first floor] -> [first floor contains kitchen]
As you can see my semantic store can already represent classes, relationships between classes, new relationships (‘contains’), relationships between relationships (‘same as’). For such a small amount of code it’s quite surprising what this system can now handle in terms of knowledge representation and simple reasoning.
Next time I get some spare time I’ll hook it up to the actual home model so you can start to query that in much more powerful ways than before.
Stay tuned!
A great video explaining the Semantic Web
May 11th
Posted by Ian in Commentary
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Web 3.0 from Kate Ray on Vimeo.