Technical Ramblings

Read Masahide’s notes on XSLT+Image Regions. Used some tools to convert my flickr photos to RDF.

Converted an XSLT Stylesheet to a different result format. Loaded ~400 RDF files into a Model, totalling 33,000 statements. Added an option to my Sparql Interface. Changed the default query. Made the extra option add the stylesheet.

Ran a query. Tweaked until it worked. Typed it all up here, to share with all of you.

Hooray for masahide, flickr, and all kinds of other wonderful things.

Dave released a new Raptor and new Rasqal today. I’ve built both, and rebuilt my Python bindings so I no longer get segfaults (Almost thought it was a bug, then Dave reminded me of previous “bugs” which were my fault).

As a result, all of my tools on both zeus and athena are now running the latest and greatest in the way of SPARQL, meaning the new query syntax (and I believe, new XML output syntax). I still need to update the examples on my PHP pages, but julie’s code is all up to date.

While I was at it, I took the oppourtunity to do some cleanups that I’ve been wanting to do for a while: You can see the revisions on the rdfpython trunk in trac’s timeline, but here’s a summary:

* Did some rewriting on mortenf’s smusher. I now get owl:sameAs triples in the store, so I have a reversible process to some extent for smushing, as well as making the smusher look for the shortest URI rather than just grabbing the first node it sees as “canonical”. Of course, I did this after a lot of URIs got tossed in my last smushing run… ah well, live and learn.
* Moved more code to use the “parse_anything” function that I wrote, which uses heuristics and logic to try and guess what kind of content we’re dealing with. It depends a lot on Content Types, but is also something I can edit and reload without restarting the bot, which is a major boon for me. This means that if something is broken, I can fix it, and make it more robust, without any kind of guilty concious about flooding channels with joins/parts/quits.
* GRDDL support (with newest raptor) in parse_anything. Since ^add is really now parse_anything, this means that if you add a page with a GRDDL description Redland supports, you’ll get the triples out of it.
* Heuristics of queries, guessing which is which. (Really ‘dumb’ right now: it just looks for ” {“, and considers it Sparql if it has it.)

What does this mean to you, dear user?

Well, quite simply, it means that you will probably support more formats (RSS, SVG, HTML+GRDDL, Atom, Turtle, ntriples) with less work (it’s all done through ^add). You can run queries in either the old format (RDQL) or new format (Sparql), or store either one.

I’d say that’s a benefit.

Thanks to Dave for getting new Redland stuff out the door.

Apparently the anxious type, Greg Williams has thrown together an RDF Query implementation in Perl, with support for the new SPARQL draft as of yesterday.

The library also offers ORDER BY support, something that I’m sure Greg is happy to have for his MT-Redland. Ordering things by date for me is something that I’ve sidestepped, but I’m not looking forward to when I actually have to deal with it.

The code uses Parse::RecDescent to generate a query based only on the SPARQL grammar. Greg mentions that it is slow: most of the time is actually in generating the Query from the Grammar.

If only I was still a Perl hacker… sadly, I’m not, so I suppose I’ll just have to start working on my C in order to help get Redland working with the new draft. (Dave estimates that it will take him about 1.5 months to catch up to the most recent WD of SPARQL.) I’d really love to just be able to use the tools I’ve already written in Python, rather than switching to Perl, or even another backend than Redland. It has worked so well for me so far.

Still, this is the first SPARQL implementation using the new Draft that I’m aware of, even if it is mostly just a hack job, so I think that it’s pretty cool, and my props are out to Greg for his work on it!

A new version of the SPARQL Working Draft released today. Congratulations to the specification editors, Eric and Andy.

Major change in syntax from the previous version: Rather than using the tuple type query syntax (?a ?b ?c) (?a ?d ?e), the query format has changed to be more turtle-like: (?a ?b ?c; ?d ?e .) This is nice, because it lets you merge data entry and data query: I can add a turtle statement <#crschmidt> a foaf:Person; foaf:nick “crschmidt”. and then query for all other people like that: (?p a foaf:Person; foaf:nick ?n.).

Another thing that was mentioned to me the other day is that the new query format doesn’t allow the optional commas between variables you select. So, SELECT ?p, ?n will now be SELECT ?p ?n. Not a big deal, but something that’ll bite me in the butt quite a bit as I get used to the switch.

I currently track Redland/Rasqal releases for querying, so I’m going to be following along with dajobe as he works to get his Rasqal engine to switch to the new format. I know he’s already working on it, and I’m looking forward to being able to show off the new syntax in some of the tools I use, from the sparql interface to julie to the IRC version of the bot. I may even try my hand at one of the later tarballs and see how little C I actually know, and try and figure out if I can help in any way.

All in all, a major new release, so if you’re using SPARQL, pay attention!

Today, I was working with the XTech Stuff, and decided I wanted to offer some fun Redland-based queries against it. Since the entire website is in PHP, I decided to stick with that theme, and write some PHP code.

I had the PHP bindings installed from a couple days ago, for… something I don’t exactly remember. I had some grand goal in mind… oh, right, I was going to provide my logo information in RDF, and parse it out using PHP.

Something I realized today is that there is no decent Redland Wrapper class like there is for Python and Perl. SWIG provides interfaces, but that basically just gets you to the level of the C API, which is something that is a bit low level for me.

To resolve this, I’ve written a PHP Wrapper class, which I hope to maintain and improve upon. It is stored in a subversion repository: you can check it out using:

svn co http://crschmidt.net/svn/redland/

Please feel free to use the trac project to help with the project.

Status: Beta Quality. Has only been tested using included test.php script. Does not do proper memory checks in any/most cases.
License: This wrapper is released under the same license as Redland itself.
Homepage: phpwrapper.

Earlier, I posted about extracting SVG metadata with Redland. However, one of the problems with this is that there isn’t a whole lot of SVG out there, nor is there a whole lot of SVG with metadata out there.

One solution to this is the OpenClipArt Library – thousands of Public Domain SVG images with embedded metadata, totalling a heck of a lot of RDF information that could provide an interesting example of how RDF information can be used in real world scenarios.

However, the metadata provided by this library was, when I looked at it, broken RDF. I sent an email to the clipart list explaining the problems with their metadata, and received friendly and helpful replies letting me know that the data was generated with the SVG-Metadata perl library.

This weekend, I downloaded that code and began working on it, submitting a patch to the maintainer (who is also one of the founders of the Inkscape project, and works on OpenClipart), which was integrated today, improving their license support (now supporting all Creative Commons licenses) and their RDF output (such that it validates).

A new version has been released, uploaded to CPAN, and will soon be propogating its way to the CPAN archives. New SVGs uploaded to openclipart will contain metadata which is valid RDF, and Bryce is looking into regenerating the data on older SVGs as well.

More RDF. Better metadata. That’s something that I think I can live with.

One of my eventual goals is to have julie replace all the features of wh4 (libby’s query bot) and foafbot (edd’s community IRC bot). One thing that edd’s bot did that julie doesn’t is to verify data based on signed documents, and to use this information as a “provenance” for the data: not just “where was it said”, but actually verifying “who said it”.

Dealing with GPG is not nearly as easy as I really think it should be. Take Redland as an example: You can interact with the library at all kinds of levels, from the base swig wrapper to the hand-written RDF.py module wrapped around it, and you can do just about anything the base library does from within Python.

GPG, on the other hand, is very hard to work with from a library level. There is a Python module for working with GPG, but it equates to simply using the command line tool in the end. You can’t tell it “Check this document”: you basically just have tools to create a pipe to GPG, and pass the options in the same way you would on the command line. Add to that that it’s Yet Another Dependancy which is somewhat of a pain to resolve in Python, and you can see why it’s slightly annoying for people who might want to use GPG.

Wondering what edd had done for FOAFbot back when it was running, I decided to grab his code and play with it. Turns out he just opened a pipe to gpg using the commands module in Python. This seemed simple enough to me, so I ripped out some of his code and turned it into a little script.

With that, I announce the release of rdfgpg, a tool for verifying the signature described by an RDF document. It uses the Redland Python bindings, and the usage is:

python rdfgpg.py http://example.org/urlof.rdf

Optionally, you can add a second argument, to set the debug argument, which will show more information about what’s going on in the background, which may help if something that you expect to work isn’t. Additionally, you can easily import the module and use the function rdfgpg.verify_url(url), which returns a list of email addresses on the signing key.

The code is released under a GPL 2.0 license, and is stolen in large part from the FOAFbot code released by Ed Dumbill. Feature requests via comments or email.

Hopefully with this, I’ll start to actually use it in my tools, to verify provenance when possible, and to start convincing people to sign their files. I hate to think what would happen to the semantic web if people suddenly started creating lots of false documents… but hopefully it’s not quite that popular yet.

How to Parse SVG Metadata, the Redland + Python way:

import urllib
import xml.dom.minidom as minidom
import RDF

m = RDF.Model()
p = RDF.Parser()
u=urllib.urlopen(“Location Of SVG File”)
svg = u.read()
doc = minidom.parseString(svg)
p.parse_string_into_model(m, doc.getElementsByTagName(“rdf:RDF”)[0].toxml(), “Location of SVG File”)
print m

In other words: Bring in the RDF and minidom modules, Create an RDF model and parser, download the SVG file to a string, parse the string into a minidom compatible variable, then look for RDF in the SVG file, parsing it into the model, and serializing the model.

Problems: What if someone uses something that’s not rdf: as the prefix?
Solutions: mattmcc offers that minidom supports getElementsByTagNameNS, so the parse line would become:
p.parse_string_into_model(m, doc.getElementsByTagNameNS( “http://www.w3.org/1999/02/22-rdf-syntax-ns#”, “RDF”)[0].toxml(), “Location of SVG File” )
resolving the Namespace issue.

Of course, since this is Redland, this is taken care of for you. Rather than doing it in this way, which is specific to SVG, we can scan for RDF in any XML doc. Simply:

import RDF
m=RDF.Model(); p=RDF.Parser()
p.set_feature(“http://feature.librdf.org/raptor-scanForRDF”, “1”)
p.parse_into_model(m, “URL Of SVG File”)

There are a number of other features you can use with a Parser. They are available via rapper -f help, but here’s a list: assumeIsRDF, allowNonNsAttributes, allowOtherParsetypes, allowBagID, allowRDFtypeRDFlist, normalizeLanguage, nonNFCfatal, warnOtherParseTypes, checkRdfID.

Naturally, Redland already does what I want it to do. Another pat on the back for Dave (and thanks to him for pointing it out).

So, a while ago, I was bored and wanted to add something to my todo list. So I created a URI for a todo namespace, and used it a couple times via the ^addturtle function built into the julie IRC bot.

As usual with my todo methods, I totally forgot about it. Recently, I brought julie into a new IRC channel (#svg) and she met raxor, who immediately started going through her commandlist:

13:15:07 < julie> Current commands: allRelated, olb, like-pubs, maintainer, webpage, drankbeerwith, like-same-music-as, alldayevents, depiction, based_near, icbm, keywords, country-population, kissed, todo, authorlinks, like-musicalwork, like-books, title, rsslinktitles, country-background, languages, nick, neighborhoods, commentContains, pub-address, schemaweb, desc, homepage, workplace, available, country-lowestPoint, knows, quote, school, sha, ljinterests, xfn_met, members, country-highestPoint, rangeOf, term, made, name, places, agentknows, dob, like-musicians, domainOf, modified, picOfA, newdepiction, rsstitles, weblog, contact, javaPlatform, biodob, mbox, dranklagerwith, namefromany, rsslinks.

Wondering what todo was, he tried it, and got a todo item I had added long ago. I replied, “Oops. Never did that.” and went to work on investigating how I could make the todo feature more useful.

In the process, I added a command to julie to add a todo item given a string:

^todoItem document built ins

Will add for me a todo item of the following turtle:
[a todo:Item; todo:owner [a foaf:Person; foaf:nick “crschmidt”]; dc:date “currenttime”; todo:text “text given”].

It will then query the model for all existing todo items for me, and return that.

Of course, this has problems: one of them being I have no way to mark a todo item as “done” once it is, and other similar things, so I will have to work a bit more on the interface to the todo list, but it’s interesting, and I thought maybe other people might want to know about it.

I do need to start documenting the built ins like this: listeningTo is another example. They don’t have a ^commandinfo result, so I’ll have to improve julie’s built in help.

julie may also see some codepiction/path searching in the near future: Greg Williams (aka kasei) gave me some Perl code that he uses to find shortest paths in a Redland store, so I’ll hopefully be able to use that and build it into julie. Also need to get code back into subversion: I screwed up my working directory so that it’s not managed in subversion, so I haven’t checked in in weeks. (This was the same problem I had last time, when someone sent me a complete refactoring of julie – only he had done it against SVN, which wasn’t up to date.)

This isn’t as polished as my usual posts: I think sometimes I overthink what I’m writing a bit, so you may see a bit more “Hey, this is my cool semantic web trick of the day” posts in the future.

What I posted about yesterday was obviously too ridiculously difficult to actually be a real solution to the problem. So, I set about making something that works at least a little bit better.

It’s possible to generate “TRM”s for songs you have. These TRMs are basically accoustic identifiers for the track: they let you identify the song based on the way it sounds. This is how Musicbrainz does its identification. Yesterday, I installed a bunch of musicbrainz stuff in an effort to get this working, and did end up finding something that will generate TRM files. My current song, Chumbawumba’s Tubthumping, has a TRM of 776643d0-9b47-4eb9-8d29-608fa9ccedcd.

So, I can generate TRMs: but that doesn’t get me very far. Now, I need to figure out the actual track associated. Since I’m doing this mostly non-interactively, I’m just going to use the most popular track with that TRM. (This doesn’t always work: for me so far this evening, it’s given me a ~80% accuracy rate). So, I fetch the RDF version of the TRM file: this can be retrieved from http://musicbrainz.org/trmid/776643d0-9b47-4eb9-8d29-608fa9ccedcd for the song I mentioned earlier.

The first song in the “tracklist” RDF bag is the one that is the best match, so I’ll grab that Track. I can then add that URI, and fetch the creator ID from that file. All these files can be tossed into the general RDF model I keep lying around, along with the turtle that I mentioned in the earlier entry: [a foaf:Person; foaf:nick “crschmidt”; menow:hasStatus [a menow:Status; dc:date “timestamp”; menow:listeningTo <trackuri>]].

Then, I can issue a query against the model: since I know the time, I only return the most recent result:

select ?t, ?n, ?d where (?p foaf:nick “crschmidt”) (?p menow:hasStatus ?s) (?s dc:date ?d) (?s menow:listeningTo ?o) (?o dc:title ?t) (?o dc:creator ?a) (?a dc:title ?n) AND ?d =~ /timestamp/

The end result? A couple hundred extra triples loaded into the global model, and I can see:

23:23:56 <crschmidt> ^listeningTo 776643d0-9b47-4eb9-8d29-608fa9ccedcd
23:24:02 <julie> 2005-03-30T04:24:01Z Tubthumping Chumbawamba

Some of the tracks I’ve been listening to tonight can be shown via:^q select ?t, ?n, ?d where (?p foaf:nick “crschmidt”) (?p menow:hasStatus ?s) (?s dc:date ?d) (?s menow:listeningTo ?o) (?o dc:title ?t) (?o dc:creator ?a) (?a dc:title ?n) AND ?d =~ /2005-03-30/. Feel free to stop by #julie on irc.freenode.net and try it!
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