, MkII is a website I’ve made last February to ease a very common task in the life of RDF developers and SPARQL users: looking up namespace URIs. A short summary of what the site can do for you is available here.

The site was developed during a few weekends, and I haven’t touched the code since I first deployed it. Today I’m publishing the first serious update to the site. This post describes what’s new.

Reverse lookup. One of the most requested features is reverse lookup. You can now enter a URI of an RDF term into the query box on the start page, and the site will respond with the best prefix for contracting that URI into a QName. This functionality is also available as an API.

Negative votes. The site has received a moderate amount of spam, mostly from pranksters who think it would be funny to propose their own homepage as a better expansion for the foaf prefix. I’ve mostly cleaned this up manually, but I think it would be better to equip the user community with tools to handle this.

The site has always had a voting mechanism, which I intended as a tiebreaker in cases where people have submitted different URIs for the same prefix, for example in the case of the dc prefix. Starting today, you can submit both positive and negative votes. If a URI receives a certain amount of negative votes, it will be no longer shown.

New export formats. One of my favourite features is the ability to directly get output in various machine-readible syntaxes by composing an appropriate URI, such as, which produces a declaration of the FOAF prefix in N3 format. I find this handy for copy-pasting into a text editor, but also for automating things.

A few formats have been added: vann produces an RDF/XML version of the namespace mapping in the VANN vocabulary (example). xmlns produces raw XML prefix declarations (example). go redirects to the namespace URI, so you can type into your browser bar as a shortcut for opening the FOAF specification. I’ve also added a table of all supported formats.

A side effect of the introduction of VANN support is that there is now a single VANN representation of all mappings known to the site.

Tweaks and fixes. Regular users will note a number of further small changes and bugfixes throughout the site. One notable fix is to the way namespace lookups are calculated for the list of popular prefixes. Ironically, most of the lookups actually are from web crawlers that followed the links in the list itself, making the list self-perpetuating. Also, the list featured the non-existing robots prefix, because many crawlers are looking for These issues should now be fixed.

Internal changes. The site is developed in PHP, and started out as a quick weekend hack, so the initial code was a horrible mess that was hardly maintainable. I spent quite some time cleaning this up and refactoring the code into a much nicer structure that should be able to grow along with some of the additional features I’ve planned for the future. The codebase now totals some 1600 lines of PHP, CSS and Javascript.

Hidden goodies: RDFa markup and feed of latest additions. Finally, I want to highlight some features that have existed all along, but are easily missed: First, many pages contain RDFa markup, so if you want to re-use any data in your own site or application, you most likely can. Second, there is an RSS feed of the latest additions to the prefix database, and it is a neat way of learning about new vocabularies and ontologies that show up around the Web.

Bugs, comments, suggestions? Any feedback is appreciated. I did a lot of refactoring without a test harness, so it’s quite likely that a few new bugs have crept in. If you notice anything, please let me know. Also, if there is anything that you would like to see in Mk III, please share!

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