Content negotiation: bad use cases I recently observed

Given the current projects I am working on, I daily see misuse of content-negotiation methodology, particularly the misuse of the Accept and Content-type HTTP header parameters.

As you will see bellow, I came across many misuse of these HTTP header parameters: potentially by their misunderstanding, or simply by forgetting to set them properly when content is negotiated between their web servers and applications requesting pages.

In any way, people should take a greater care about setting the content-negotiation properly between their servers and other applications. In fact, I saw many examples, on many web servers: from the semantic web research groups, to the hobbyists.

The principle

The principle is simple, if a requester sends a HTTP query with the Accept header:

Accept: text/html, application/rdf+xml

The web server should check the priority of the mime types that the requester is requesting and send back the requested document type with the greater priority, along with the Content-type of the document in the HTTP header answer.

The Content-type parameter is quite important, since if a user application request a list of 10 mimes having all the same priority, it should know which of them as been sent by the web server.

Trusting the Content-type parameter

It is hard.

In fact, Ping the Semantic Web do not trust any web server that returns Content-type. This parameter is so misused that it makes it useless. So I had to develop procedures to detect the type and the encoding of files it crawls.

For example, sometime, people will return the mime TEXT/HTML when it facts it’s a RDF/XML or a RDF/N3 file; this is just one example among many others.

The Q parameter

Another situation I came across recently was with the “priority” of each mime in an Accept parameter.

Ping the Semantic Web is sending this Accept parameter to any web server from which it receives a ping:

Accept: text/html, html/xml, application/rdf+xml;q=0.9, text/rdf+n3;q=0.9, application/turtle;q=0.9, application/rdf+n3;q=0.9, */*;q=0.8

The issue I came across is that one of the web servers was sending me a RDF/XML document for that Accept parameter string, even if it was able to send a TEXT/HTML document. In fact, if the server was reading “application/rdf+xml” in the Accept parameter, it was automatically sending a RDF document to it, even if it has a “lesser priority” than theTEST/HTML document.

In fact, this Accept parameter means:

Send me text/html or html/xml is possible.

If not, then send me application/rdf+xml, text/rdf+n3, application/turtle or application/rdf+n3.

If not, then send me anything; I will try to do something with it.

This is really important to consider the Q (or absence of the Q) parameter. Because its presence, or its non-presence, mean much.

Discrimination of software User-agents

Recently I faced a new kind of cyber-discrimination: discrimination based on the User-agent string of a HTTP request. In fact, even if I was sending “Accept: application/rdf+xml”, I was receiving a HTML document. So I contacted the administrator of the web server and he pointed me out to an example available on the W3C’s web site, called Best Practice Recipes for Publishing RDF Vocabularies, which explained why he has done that:

# Rewrite rule to serve HTML content from the namespace URI if requested
RewriteCond %{HTTP_ACCEPT} text/html [OR]
RewriteCond %{HTTP_ACCEPT} application/xhtml\+xml [OR]
RewriteCond %{HTTP_USER_AGENT} ^Mozilla/.*
RewriteRule ^example5/$ example5-content/2005-10-31-docs/index.html [R=303]

# Rewrite rule to serve HTML content from class or prop URIs if requested
RewriteCond %{HTTP_ACCEPT} text/html [OR]
RewriteCond %{HTTP_ACCEPT} application/xhtml\+xml [OR]
RewriteCond %{HTTP_USER_AGENT} ^Mozilla/.*
RewriteRule ^example5/(.+) example5-content/2005-10-31-docs/$1.html [R=303]

So, in the .htaccess file they published in the article, we can see that if the user agent is “Mozilla” it will send a HTML document.

However, it is wrote in the same document:

Note that, however, with RDF as the default response, a ‘hack’ has to be included in the rewrite directives to ensure the URIs remain ‘clickable’ in Internet Explorer 6, due to the peculiar ‘Accept:’ header field values sent by IE6. This ‘hack’ consists of a rewrite condition based on the value of the ‘User-agent:’ header field. Performing content negotiation based on the value of the ‘User-agent:’ header field is not generally considered good practice.

So no it is not a good practice, and people should really take care about this.


People should really take care of the Accept parameter when their server receive a request, and send back the good Content-type depending on the document they send to the requester. Content-negotiation is becoming the main way to find and access RDF data on the Web, and such behaviors should be fixed by web server administrators and developers.

Has Robert Scoble got some incentives to ‘finally’ get what the semantic web is?

Everybody do errors and I have just done one.

Thanks for proving me that I was wrong.

I probably should have wrote a blog post about it instead of writing a comment, that way I would have been sure that you get it (like this blog post that created an instant reaction).

Robert, it seems you didn’t received my email 4 days ago, so I am sorry about that.

Anyway it doesn’t change the essence of this blog post, and my comment. This is not a good start, but a good way, to try to tie the link between the “Web 2.0” (sorry but I don’t like that term 😉 ) and the Semantic Web [academic] community. There are much things going on around that could benefit everyone.

The only thing I would like to say that people would remember is that the Semantic Web is not the result of one or a couple of companies, but the result of a Whole; the result of the interaction between all beings.

Robert, I hope you will continue to dig deeper to find all the things people are working on related with the Semantic Web. Sorry about that, and I hope you a beautiful day!

I am asking the question and I hope I am wrong.

Some days ago Robert Scoble wrote an enflaming post about what Radar Networks are currently developing. This “thing” (I refer to a “thing” because no body know what it really is (some type of semantic web system)) finally helped Robert to understand what the semantic web is.

At that moment I was happy to see that a “Web 2.0” guru understood how Semantic Web technologies could help him; how they could be used to make the World a better place to live in.

Then I told myself: “Fred, help him to see what other people are doing in that direction too. Show him what you are working on; what other people are developing too; what they are writing on the subject; Etc.”

Then I wrote that comment on his blog post:

Hi Robert,

Could I suggest a couple of reading in that direction that could potentially interest you?:


  1. Zitgist Search Query Interface: A new search engine paradigm
  2. The Linked-Open-Data mailing list
  3. Planet RDF

From there, you will be able to dig deeper into the semantic web community, the ideas it plays with, what the Web is becoming, etc.

Hope it can helps some people to eventually understand what is going on with the semweb.

Take care,


This comment has never appeared on its blog post. It seems he rejected it by moderation. I sent him an email 3 days ago and he never replayed to me.

Why Robert rejected this innocent comment? I got my idea that lead to the topic of this blog post: “Has Robert Scoble got sone incensitives to ‘finally” get what the semantic web is?”

Does Robert rejected it because I was referring to Zitgist; and that is a possible competitor to what Radar Networks is working on right now?

I have no idea, but I am always frustrated to see when bloggers doesn’t tell to their readers they got some incentives to write articles about special things.

Otherwise, why my comment got rejected? I have no idea, but I would like to know.

At the end, these people will probably have to learn that the Semantic Web is more about cooperation between people, enterprises, other entities and honesty than a more traditional way to do things and business.

I think that the Semantic Web will change things in a major way, as long as people, societies and the way we live.

Making the bridge between the Web and the Semantic Web


Many people think that the semantic web will never happens, at least in next few years, because there is not enough useful data published in RDF. This is fortunately a misconception. In fact, many things are already accessible in RDF, even if it doesn’t appear at the first sigh.



Danny Ayers recently pointed out a new web service created by Dave Beckett called Triplr: “Stuff in, triples out”.

Triplr is a bridge between well-formed XHTML web page containing GRRDL, RSS and their RDF/XML or Turtle formatting.

Here is an example


Virtuoso’s Sponger

Another bridging service called the Sponger also exists. Its goal is the same as Triplr: taking different sources of data as input, and creating RDF as output.

The Virtuoso Sponger will do everything possible to find RDF triples from a given URL (via content-negotiation and checking for “link” elements in HTML files). If no RDF document is available from a URL, it will tries to convert the data source available at that URL into RDF triples. Converted data sources are: microformats, RDFa, eRDF, HTML meta data tags, HTTP headers, as well as APIs like Google Base, Flickr,, etc.


How does it work?

  1. The first thing the Sponger is doing is trying to dereference a given URL to get RDF data from it. If it finds some, it returns it, otherwise, it continues.
  2. If the URL refers to a HTML file, the Sponger will try to find “link” elements referring to RDF documents. If he finds one or more of them, it will add their triples into a temporary RDF graph in and continue its process.
  3. If the Sponger finds microformat data into the HTML file, it will maps it using related ontologies (depending on the microformat) and will creates RDF triples from that mapping. It will add these triples to the temporary RDF graph and continues.
  4. If the Sponger finds eRDF or RDFa data into the HTML file, he will extracts them from the HTML file and add them into the RDF graph and continues.
  5. If the Sponger find that it is talking with a web service such as Google Base, it will maps the API of the web service with an ontology, creates triples from that mapping and includes the triples into the temporary RDF graph and continues.
  6. If nothing is found and that there is some HTML meta-data, it will maps them with some ontologies, creates triples and add them to the temporary RDF graph.
  7. Finally, if nothing is found, it will returns an empty graph.

The result is simple: from any URL, it is most than likely sure that you will get some RDF data related to that URL. The bridge is now made between the Web and the Semantic Web.


Some examples

There are some examples of data sources converted by the Sponger:



What is fantastic for a developer is that he only has to develop its system according to RDF to make its application communicating with any of these data sources. The Virtuoso Sponger will do all the job of interpreting the information for him.

This is where we really meet the Semantic Web.

With such tools, it is like looking at the semantic web in a lens.

Zitgist Search Query Interface: A new search engine paradigm


People start to talk about Zitgist: What is it? How does it work? When will it be released? Etc. This is the first article of a series to come that will explain the first portion of the service: the search query builder user interface. As you will see bellow, there are many considerations to take into account when dealing with the development of a semantic web search query builder.

The difference between a traditional search engine like Google and a semantic web search engine like Zitgist is that the aggregated, indexed and queried data is different. Google mostly use text files such as HTML, PDF, DOC, Etc., and Zitgist use RDF files from genuine or converted data sources.

This difference has a big impact on how users build queries to answer to their questions. Google users use keywords to try to define what they are searching for. Then the search engine will check in their database to find these keywords into the texts they aggregated and indexed.

The new paradigm introduced by semantic web search engine such as Zitgist is different: users will describe the characteristics of the subjects of their search instead of using keywords.

As you will see, the difference between using keywords and describing characteristics of subjects will have a great impact on the user interface used to build these search queries.


A first query


[Click to enlarge]


The first step is to choose which type of subject a user is searching for. In the first version of Zitgist, we let users choosing among some type of subjects: musical things such as artists, bands, albums, tracks, performances, or people, groups, projects, geographical locations, documents and discussion forums.

Once the user choose what he was searching for he has to describe the characteristics of that subject.


[Click to enlarge]

In that first example, the user tries to find a person. As you can see, there are some characteristics describing a person that can be defined by the user. Depending on the user interface (basic or advanced) more or less characteristic will be available for the description of that subject.

So the user chooses to search for a person that has the name “Chris” and that is interested in the “Semantic Web”.



[Click to enlarge]


The search engine will then return results matching subjects know by Zitgist having these two characteristics.

Using Google, the user would have use the query string “chris semantic web” that has three distinct keywords: (1) “chris” (2) “semantic” and (3) “web”. The problem is that there is no relation between these keywords. Is he searching for someone named Chris that is working in the semantic web domain or that is interested in the semantic web? Is the user searching for something else? There is no way to know. The best Google can do, is putting their algorithmic magic into action to try to find what the user is searching for, and hoping it is really what he wants.

But for Zitgist, if the person [the subject of the search] defined himself as having the name Chris and having an interest in the Semantic Web (defining himself using RDF) than we will know that the results are definitely what the user is searching for.

Note: one of the next article will be dedicated to what will happens once a user get results from Zitgist.


Describing relationship between more than one subjects

The first example was quite simple. However Zitgist’s query builder interface take all its senses once we try to push it a little further.

How a user could easily describe a subject, with its own set of characteristics, that knows another subject, also with its own set of characteristics?



[Click to enlarge]


In this example, we have a user that search for a person knows as “Alice”. But he doesn’t search for any person named “Alice”, no. This user wants to find a person knows as “Alice” that know another person named “Bob”.

As you can see in the image above, it is quite easy to do using Zitgist. The user described the subject he wants to search for: “Alice”. This subject is a person with the name “Alice” that “knows” a person called “Bob”.
As you can see, the user interface changed its color when we introduced a new subject into the query [“Bob”]. That way, users can easily see which subject they are describing.

After that, the user could always add new characteristics to Bob. He could say that Bob is interesting in writing and that he lives near London for example.



In fact, the possibilities are endless.


One more step

What is interesting with the semantic web is that anybody can describe anything. One of these interesting example is when we start to think about Document. In fact, what are documents? What describe a Document? Etc.

A document can be described with an author, a creation data, a publication date, an editor, a publisher, its medium, etc. But its content can also be described such as its topics.



[Click to enlarge]


If someone describes one of the documents he created and that explicited the topic(s) of that document, Zitgist could easily find it that way:



[Click to enlarge]


As you can see a user can search for a “Document” that as a “Person” named “Alice” that “knows” another person named “Bob” as the “Topic” of the “Document”.

So, if someone would start to describe novels that way, we could easily search for books where its protagonist is called Alice and that is living in London. Wouldn’t that be a terrific way to find books you could like to read? The only thing we need at the moment is people starting to describe books that way: hobbyist, authors or publishers.


We always knows the data we are manipulating

What is fantastic with the seman

tic web is that we always know what is the data we are manipulating. As you will see in next articles, this characteristic of the system is the main one when comes the time to talk about users interfaces. However, I will introduce it in this article using the query builder interface.



[Click to enlarge]

In the example above a user tries to find a geographic location near a certain place. However the question for the user here is: how should I describe that location? By a name? Which name? By a latitude and longitude? How to? Etc.

By the fact that we know what is the type of the data the user is looking for we can try to assist it with some widgets.

In the example above we know that the user is searching for a geographical location. Ultimately, a geographical location on Earth is defined by a longitude and latitude. So what we do is showing a map widget to the user. The only thing he will have to do is to click on the map to choose the location. That is it. The user interface widget is intuitive for users, and he doesn’t have to bother about how to describe the location.

Another example:



[Click to enlarge]


Now the user try to find a ” Music Artist” that “composed” “Albums” between “1980” and “1990”.

In such a case, how the user is supposed to describe that fact? Would he writes dates like “1980-01-03”? “1980-03-01″? ” 3 January 1980″? Etc…

Since Zitgist knows what the user is trying to describes, it only popup a small widget that will assists the user in the creation of its search query.

This is by far the greatest strength of the semantic web when come the time to talk about user interfaces. Since the interface knows what is the type of the data being manipulated, it can do a full of things to help users to do what he really want to. And what a user really want to do is certainly not asking questions like: how should I describe this thing, Etc.

And as you will see in next articles, this is just the beginning.


More information about Zitgist

There are a list of blogs post I wrote about Zitgist, explaining what the is project, its goals, its vision, its release, etc.



Zitgist’s goal is not to be a replacement to traditional search engines such as Google. In short and middle term its goal is to be complementary to traditional search engines; to be another tool in Web users’ toolkit.

As you can see by the description of this semantic web search engine query interface, the semantic web and semantic web search engines like Zitgist will be quite useful to make some order, classify and search in all the data that has been created so far and that is yet to be created on the Web.

In the next articles I will continue to roll out what Zitgist is, where we are with the project and how it integrates into the semantic web that is now emerging on the Web.

The only thing you have to do is to sit down and check the show.

No I am wrong, the only thing you have to do is board the train and continue with us by asking question, making comments and suggestions, describing your data using RDF, letting Zitgist integrating it into its database, etc.

Welcome aboard.

Dynamic Data Web Page

What is a dynamic data web page? It is a shape-shifter data source. That is it. It is a source of data that will change its shape depending on the request that has been made on the data source.


Shapes of the data source

The data source will shape the format of its output depending on what you need. If you are a human, you would like to have something that you can read and understand like a HTML web page. However, if you are a web service, you would probably like to get the data in a shape that you could easily understand such as RDF, XML, JSON, etc.

It is as simple as that: a Dynamic Data Web Page is web page that will outputs data in different formats depending on what the requesting users wants.

There are many formats:

  1. HTML – Human readable
  2. RDF/XML
  3. RDF/N3
  4. XML
  5. JSON
  6. Others could be easily implemented if needed.


In Dynamic Data Web Page there is: a Web Page and Data

A DDWP is two things:

  1. A Web Page: as we saw above, it is a way to present/publish the data of the source formatted in some way.
  2. Data: as we will see bellow, it is the source of data.

This said a DDWP is nothing else than a source of data published in some ways.


Dissection of a Dynamic Data Web Page



0. Creation of the data source. The preliminary step for the data source (triple store) is to continually index RDF data sources. If we are talking about a generic service, then it should aggregate RDF data from everywhere: the Web, specialized databases such as Musicbrainz, Wikipedia, etc. If it is a specialized system such as the products catalogue of a company, it should constantly synch its triple store with the catalogue. This constant operation will create a valuable data source.

1. Creation of a SPARQL query. An end user wants information. This end user can be anything: a user, a developer, a web service, etc. This user will build a SPARQL query that will returns the results from the data source.

2. Saving the SPARQL query. The SPARQL query will then be saved on the web server of the service. As soon as the query will be saved on the server.

3. Assigning a URL to the SPARQL query. A URL will be assigned by the web server for that saved SPARQL query. From there, anybody will be able to access to the results of the query by looking at that URL.

4. Accessing the URL

4.a. Sending the HTTP query. In our example, a web service tries to get the results returned by the SPARQL query from the DDWP. To get them, it will send a HTTP query to the web server for that URL.

4.b. Doing content negotiation with remote server. However, the web server wants a XML representation of the results since it is the only format it understands. This request will be done via content negotiation with the web server. It is where the shapes of the DDWP are important: depending on want the user want, results of a SPARQL query will be formatted in one of the possible shapes, depending on what the user wants (content negotiation), and will send them to him.

5. Generating the DDWP according to the content negotiated. The Dynamic Data Web Page will be generated by the web server depending on the content negotiation the two parties agreed on.

6. Sending results to the web service. Finally the results, formatted to meet the user’s needs, will be returned to the user.


What this means?

This means that data only matters. In fact, the only thing one need now is to build a good data source. Once the data source is well built (remember, the data source can be anything here, from a search engine database to the products catalogue of a company, or even the personal web page of a 14 years old geek).

From that data source, everything can be generated for each web page (URL). If the content requested is a HTML page, then the data source can generate XML, run a XSLT skin template with and then send a HTML page: just like any other web page. However, from the same data source, a semantic web crawler could request the RDF/N3 data for the same URL. Then the DDWP would send the RDF/N3 representation of the URL.

So from one data source, you can get its data the way you want.

From that point a URL (or a web page, call it the way you want) become a presentation page web, a web service, etc; All-in-one!


Some examples

Everything is made simpler with examples, so there we are. All the concept of Dynamic Data Web Page is possible thanks to Virtuoso. All the examples above are using this database management system.

Okay, to illustrate the case, we will use this Google Base Jobs page for example:

Step #0

The triple store will get that Google Base Jobs page, convert it into RDF and then will index the triples into the triple store. This will be the data we will try to access.

Step #1

A user created a SPARQL query that will request all that data. The query look-like:

SELECT ?s ?p ?o
FROM < jobs?start-index=30&max-results=30&key= ABQIAAAA7VerLsOcLuBYXR7vZI2NjhTRERdeAiwZ9EeJWta3L_ JZVS0bOBRIFbhTrQjhHE52fqjZvfabYYyn6A>
?s ?p ?o .

Step #2

The user will save the SPARQL query on the web server in the directory “/DAV/home/demo/Public/Queries/DataWeb/” with the file name “google_base_jobs_dataspace.isparql”

Step #3

The web service will assign a URL to that file: Queries/DataWeb/google_base_jobs_dataspace.isparql

Now the user wants to see the results of the query he just built, he can see them only by putting this URL into its web browser. Then a HTML web page will be generated and displayed so that he can easily consult it.

This is a generic html page. But what about generating XML instead of HTML and then applying a XSLT skin template to generate the HTML for the user? Yeah, you just got another way to create traditional dynamic web pages.

Step #4.a / #4.b / #5 / #6

Now what we want is showing what happen when a web service request results not in HTML but in something else like RDF/XML.

To show you how it happens, we will use the OAT RDF Browser. This is a web service that will get RDF data from somewhere on the Web and that will display it to users via a web interface.

This web service do exactly the steps 4, 5 and 6: it send a HTTP query for a URL. It will do some content negotiation with the remote web server to get RDF data, it will download the RDF data sent by the web server, consume it and display it to the user via the interface.

The result for our example is there. As you can see, from the same URL, the DDWP will send RDF/XML data instead of HTML. Then the web service will consume it, and display the same information in a different way. How different? Well, click on the Yahoo! Map Tab and you will see. You see? The same information displayed on a map that shows where the jobs are in the United-States.



Dynamic Data Web Page is not a theory. It is a reality; it is something that already exists in Virtuoso and that can be used by anyone who cares about simplifying the exchange of data between its system and other systems. It is all about Web communication. Instead of talking about language (real world) we are talking about formats (web world).