cygri’s notes on web data

TopBraid Composer, the commercial Eclipse-based ontology editor developed by Holger Knublauch and colleagues at TopQuadrant, supports D2RQ in its latest release.

Holger says:

A common request from our customers is the ability to reuse existing (legacy) databases in the context of an RDF/OWL project. The mapping of relational databases into RDF is non-trivial and since I am not at all an expert on databases, I turned to the Web to find help. From some other entry on Planet RDF, I dimly remembered that Chris Bizer has been working on this, and linked from his pages I discovered D2RQ.

TopBraid and D2RQ are both Jena-based, so integrating them was not hard.

Now we can browse D2RQ-mapped database content in a nice GUI, and use a professional ontology editor to customize D2RQ mapping files. Pretty cool!

Maintaining my FOAF file involves a lot of work: I have to write RDF/XML by hand, calculate SHA1 hashes, and enter a lot of information that is already stored in a different place: my address book.

That’s why I have created an AppleScript that does all the work for me at the press of a single button. It will even upload the FOAF file to my website using FTP. FOAF on the Mac has never been easier!

The script hasn’t been tested in any other environment, but if you want to try it, here are the instructions. If you do, please comment below and tell us how it works for you.

Requirements

• Mac OS X, tested on 10.4 only
• The script uses Cyberduck, a nice and free FTP client – just download and drop in the /Applications folder

Download and installation

• Download the Export Address Book to FOAF script and put it somewhere convenient, e.g. into the /Applications folder
• Double click the script to run it – by default, it will create a file called foaf.rdf on your desktop (be patient, it’s slow)

Configuration

• To enable FTP upload, or to customize the location where the foaf.rdf file is created on your hard disk, open the script in Script Editor (found in /Applications/AppleScript), and change the configuration at the top of the file
• A good configuration would be to upload the file as foaf.rdf to the directory of your home page
• Save the file

Preparing your card

• If you don’t have a card for yourself in your address book, then create a new one and choose Make This My Card from the Card menu
• Provide as much information about yourself as you like

Preparing your public contacts

Optionally, your FOAF file can contain references to some of the people you know – the public part of your social network. To set this up in Address Book:

• Create a new Group called “Public Contacts” (upper case P and C)
• Drag some cards to this group
• It’s good etiquette to only add people who already have some kind of presence on the Web
• Only their name, home pages, and an encrypted form of their email address will be published by the script; phone numbers, birthdays, notes etc remain private

Weaving the Semantic Web

FOAF files are a part of the Semantic Web, a worldwide decentralized web of data. Optionally, you can add some additional information to your card and the cards of your public contacts, to weave your FOAF file into the Semantic Web.

All of these additional pieces of knowledge go into a card’s URL fields which you can add using Card » Add Field » URL. The green plus adds multiple URLs. There are a number of different URL types, click the label on the left to choose one. Some types may have to be added using the Custom … option. These are the supported types:

home page: The person’s personal home page, if they have one.

weblog: The person’s web log, if they have one. It doesn’t really matter if you choose home page or weblog.

work: The home page of the person’s employer, department, or group.

img: An image of the person on the Web. This works only for your own card.

URI: If the person has chosen a URI to identify herself, then add it with this label. You can also use this for yourself. My URI, for example, is http://richard.cyganiak.de/foaf.rdf#cygri.

RDF: For those of your public contacts who already have a FOAF profile, you can add the profile’s URL using this label. Please do this if you can spare a bit of time. For yourself, you can use this label to add other RDF files that contains additional information about you.

Make sure that all URLs include the leading http:// bit.

As I said above, feedback is very welcome.

This snippet calculates the SHA-1 digest of a string:

set s to "mailto:richard@cyganiak.de"
do shell script "echo -n " & quoted form of s & "|openssl sha1"
set digest to result

This is useful for calculating foaf:mbox_sha1sum values, for example.

Dan Connolly complained on rdfweb-dev about FOAF’s redundant inverse properties (depicts/depiction, page/topic), and pointed to this TimBL post, which mentions a nice pattern for designing RDF vocabularies that should be adopted more widely.

Avoid inverse properties. There’s no need to clutter your namespace with redundant inverse properties. Have either ex:parent or ex:child in your vocabulary, but not both. It doesn’t really matter which; just pick one and stick with it. That way, there are less ways to express the same thing, and that’s good for interoperability.

Of course, if you find out that someone else has independently invented an inverse of your property, then linking to it using owl:inverseOf is a good idea.

Display back links just like forward links. I’m doing this the wrong way in D2R Server‘s RDF browser. Here’s a screenshot showing an RDF representation of this blog’s Semantic Web category (click to enlarge):

The category has three “forward” properties: It has a type of skos:Concept, a prefLabel of “Semantic Web”, and a page about it at http://dowhatimean.net/category/semantic-web/.

It also has a bunch of “backward” properties: It is the subject of a number of blog posts. These point “the other way”, that is, from some other resource to the category. The category is the object of the RDF statement, not the subject.

I’m displaying the two types of properties in two different columns. A better way would be to use a single column, and use rdfs:labels instead of QNames for the properties: has type instead of rdf:type, and is subject of instead of skos:subject. Someone browsing the Semantic Web doesn’t care about the distinction between forward and backward properties, they just need to know that the resource is linked to some other resource. And therefore both should be visually represented the same way.

Provide inverse labels in vocabularies. But where do I get this “is subject of” label from? Vocabulary authors usually attach rdfs:labels to their properties, and they work beautifully in the forward case, but there is no rdfs:backwardsLabel that could be used in the backwards case.

Here’s Tim’s solution: Introduce an anonymous inverse property and attach the label to it.

skos:subject rdfs:label "has subject" .
skos:subject owl:inverseOf [ rdfs:label "is subject of" ] .

I think it’s a beautiful solution, and building the Semantic Web would become easier if it was widely adopted by vocabulary publishers.