RDFWeb and Friend of a Friend (FOAF): FOAF Checker utility for PGP-signed FOAF profiles

June 24, 2003

FOAF Checker utility for PGP-signed FOAF profiles

Ken MacLeod has announced a new tool, 'FOAF Check', which reads a FOAF file, checks its PGP signature and extracts portions of the RDF, eg. for inclusion in weblog comments (via. Movable Type cookies etc.).

This approach provides a way to avoid re-entering the same data over and again across multiple sites - you just point them at your FOAF document and let them read what you've already said about yourself. Ken's writeup points to previous work on FOAF/PGP-based decentralised profiles.

This is really cool, basically. Looking at the detail it does suggest we need to do a little more work on the FOAF vocabulary for clarifying which of several people mentioned in any given FOAF file is the topic of that file. There are currently several ways we could indicate this; one needs to be picked and documented more clearly in the FOAF spec. It also isn't immediately clear (to me!) how we get from knowing that a FOAF file validates against some PGP key to knowing that the PGP identity is the one that our application wants it to be. But it's a step in the right direction...

Also the combination of foafbot and tools like foaf-check provide good reason for people to actually start using PGP (or GNU Privacy Guard (GPG), the Free GNU version), That can only be a good thing.

One other topic this throws up: is it reasonable to expect people to remember and quote their FOAF URLs? Or should we ask for their homepage, and look for a LINK REL in their homepage markup pointing to their FOAF data? Posted by danbri at June 24, 2003 06:37 PM | TrackBack

Comments

See also Ken's notes in the FOAF wiki, http://rdfweb.org/topic/FoafIdentityAssurance for more details on how this might be used for a challenge/response style of authentication.

Nearby, FOAF's wiki homepage (recently tidied up somewhat), http://rdfweb.org/topic/FoafProject

Posted by: Dan Brickley on June 24, 2003 09:11 PM

"Looking at the detail it does suggest we need to do a little more work on the FOAF vocabulary for clarifying which of several people mentioned in any given FOAF file is the topic of that file."

I think this is very important, especially for anyone who wants to write a very simple tool and have it work OK with FOAF files which might provide circular references between the people described (as I've certainly experienced with FOAF files in the wild).

It would make sense (to me at least) to enforce the use of an rdf:Description element as documented on http://www.semanticplanet.com/library/DescribingRdfDocuments but there are probably other ways, and possibly better ones too.

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We can see an example of this in our code we've written so far. In each function's block, we declare variables that hold our data. When each function ends, the variables within are disposed of, and the space they were using is given back to the computer to use. The variables live in the blocks of conditionals and loops we write, but they don't cascade into functions we call, because those aren't sub-blocks, but different sections of code entirely. Every variable we've written has a well-defined lifetime of one function.

Posted by: Botolph on January 20, 2004 08:00 AM

Being able to understand that basic idea opens up a vast amount of power that can be used and abused, and we're going to look at a few of the better ways to deal with it in this article.

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Inside each stack frame is a slew of useful information. It tells the computer what code is currently executing, where to go next, where to go in the case a return statement is found, and a whole lot of other things that are incredible useful to the computer, but not very useful to you most of the time. One of the things that is useful to you is the part of the frame that keeps track of all the variables you're using. So the first place for a variable to live is on the Stack. This is a very nice place to live, in that all the creation and destruction of space is handled for you as Stack Frames are created and destroyed. You seldom have to worry about making space for the variables on the stack. The only problem is that the variables here only live as long as the stack frame does, which is to say the length of the function those variables are declared in. This is often a fine situation, but when you need to store information for longer than a single function, you are instantly out of luck.

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Note the new asterisks whenever we reference favoriteNumber, except for that new line right before the return.

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The Stack is just what it sounds like: a tower of things that starts at the bottom and builds upward as it goes. In our case, the things in the stack are called "Stack Frames" or just "frames". We start with one stack frame at the very bottom, and we build up from there.

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Note the new asterisks whenever we reference favoriteNumber, except for that new line right before the return.

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This is another function provided for dealing with the heap. After you've created some space in the Heap, it's yours until you let go of it. When your program is done using it, you have to explicitly tell the computer that you don't need it anymore or the computer will save it for your future use (or until your program quits, when it knows you won't be needing the memory anymore). The call to simply tells the computer that you had this space, but you're done and the memory can be freed for use by something else later on.

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