Check out the first post of the Problems of Linked Data series. The subject of the post is the identity of Linked Data:

In mid-2009 Paul Miller asked the question Does Linked Data need RDF?. He stated that the idea that Linked Data can only be Linked Data if expressed in RDF is a dogmatism that makes him „deeply uncomfortable“. A big debate questioning (once basic) assumptions of Linked Data began, and there is still no consensus today.

The problem arose because of the imprecise definition of the Linked Data rules that can be interpreted in different ways. The document that defines Linked Data and its rules is a personal note by Tim Berners-Lee and hasn’t been formally approved by the W3C. Even the term “Linked Data” itself is controversial and contributes to the confusion in the sense that the exact concept of “Linked Data” is conflated with the general idea of linking (any) data. Anyway, the third rule for publishing Linked Data has led to the most confusion and debate:

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Stay tuned, more to come soon!


Check out the new blog post Problems of the RDF syntax:

An RDF syntax (notation) is a concrete syntax for writing (serializing) RDF triples. There are many different notations, some of which are based on existing formats (XML, (X)HTML, JSON), while others use special formats (Turtle).

The problems of the RDF model, discussed in the previous posts, are inherited by RDF notations. Various special cases require special support in a syntax, which makes it more complex. However, RDF notations contain a number of their own problems, which can be divided into two categories:

  • various problems in RDF notations
  • the lack of a single dominant notation
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Check out the new blog post The Ultimate Problem of RDF and the Semantic Web on

In the previous posts I’ve covered two important problems of the RDF model, related to blank nodes and literals. Here, I’m going to focus on what I think is the key problem of RDF – the problem of the node of an RDF graph.

In the RDF: Concepts and Abstract Syntax, a node is defined as follows:

“The set of nodes of an RDF graph is the set of subjects and objects of triples in the graph.”

It then states that a node can be a URI reference, a literal or a blank node. However, the concept of a node itself is not clearly defined. What is it that is common to all different types of nodes? What requirements does a node need to meet in order to be a node?

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Check out the new blog post on my new (personal) blog. It’s the first post of the series on the results of my recent research, regarding the realisation of the Web of data/the Semantic Web. The first part is about the problems of the RDF model and the subject of this post are blank nodes:

Nodes without a name represent a special kind of nodes called blank nodes (bNode). These nodes simply indicate the existence of a thing, without using, or saying anything about, the name of that thing. Therefore, they are referred to as existential variables of an RDF graph.

Due to the absence of a name (URI), manipulating data containing blank nodes is much harder – they make otherwise trivial operations far more complex. They complicate the lives of data consumers, especially if data changes in the future. Blank nodes add a lot of complexity to the standards built upon them, and the implementations consuming them. They are poorly understood and difficult for beginners.

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