Tag Archives: rdf

Web Art/Science Camp — how web killed the hypertext star and other stories

Posted on by

Had a great day on Saturday at the at the Web Art/Science Camp (twitter: #webartsci , lanyrd: web-art-science-camp). It was the first event that I went to primarily with my Talis hat on and first Web Science event, so very pleased that Clare Hooper told me about it during the DESIRE Summer School.

The event started on Friday night with a lovely meal in the restaurant at the British Museum. The museum was partially closed in the evening, but in the open galleries Rosetta Stone, Elgin Marbles and a couple of enormous totem poles all very impressive. … and I notice the BM’s website when it describes the Parthenon Sculptures does not waste the opportunity to tell us why they should not be returned to Greece!

Treasury of Atreus

I was fascinated too by images of the “Treasury of Atreus” (which is actually a Greek tomb and also known as the Tomb of Agamemnon. The tomb has a corbelled arch (triangular stepped stones, as visible in the photo) in order to relieve load on the lintel. However, whilst the corbelled arch was an important technological innovation, the aesthetics of the time meant they covered up the triangular opening with thin slabs of fascia stone and made it look as though lintel was actually supporting the wall above — rather like modern concrete buildings with decorative classical columns.

how web killed the hypertext star

On Saturday, the camp proper started with Paul de Bra from TU/e giving a sort of retrospective on pre-web hypertext research and whether there is any need for hypertext research anymore. The talk brought out several of the issues that have worried me also for some time; so many of the lessons of the early hypertext lost in the web1.

For me one of the most significant issues is external linkage. HTML embeds links in the document using <a> anchor tags, so that only the links that the author has thought of can be present (and only one link per anchor). In contrast, mature pre-web hypertext systems, such as Microcosm2, specified links eternally to the document, so that third parties could add annotation and links. I had a few great chats about this with one of the Southampton Web Science DTC students; in particular, about whether Google or Wikipedia effectively provide all the external links one needs.

Paul’s brief history of hypertext started, predictably, with Vannevar Bush‘s  “As We May Think” and Memex; however he pointed out that Bush’s vision was based on associative connections (like the human mind) and trails (a form of narrative), not pairwise hypertext links. The latter reminded me of Nick Hammond’s bus tour metaphor for guided educational hypertext in the 1980s — occasionally since I have seen things a little like this, and indeed narrative was an issue that arose in different guises throughout the day.

While Bush’s trails are at least related to the links of later hypertext and the web, the idea of associative connections seem to have been virtually forgotten.  More recently in the web however, IR (information retrieval) based approaches for page suggestions like Alexa and content-based social networking have elements of associative linking as does the use of spreading activation in web contexts3

It was of course Nelson who coined the term hypertext, but Paul reminded us that Ted Nelson’s vision of hypertext in Xanadu is far richer than the current web.  As well as external linkage (and indeed more complex forms in his ZigZag structures, a form of faceted navigation.), Xanadu’s linking was often in the form of transclusions pieces of one document appearing, quoted, in another. Nelson was particularly keen on having only one copy of anything, hence the transclusion is not so much a copy as a reference to a portion. The idea of having exactly one copy seems a bit of computing obsession, and in non-technical writing it is common to have quotations that are in some way edited (elision, emphasis), but the core thing to me seems to be the fact that the target of a link as well as the source need not be the whole document, but some fragment.

Paul de Bra's keynote at Web Art/Science Camp (photo Clare Hooper)

Over a period 30 years hypertext developed and started to mature … until in the early 1990s came the web and so much of hypertext died with its birth … I guess a bit like the way Java all but stiltified programming languages. Paul had a lovely list of bad things about the web compared with (1990s) state of the art hypertext:

Key properties/limitations in the basic Web:

  1. uni-directional links between single nodes
  2. links are not objects (have no properties of their own)
  3. links are hardwired to their source anchor
  4. only pre-authored link destinations are possible
  5. monolithic browser
  6. static content, limited dynamic content through CGI
  7. links can break
  8. no transclusion of text, only of images

Note that 1, 3 and 4 are all connected with the way that HTML embeds links in pages rather than adopting some form of external linkage. However, 2 is also interesting; the fact that links are not ‘first class objects’. This has been preserved in the semantic web where an RDF triple is not itself easily referenced (except by complex ‘reification’) and so it is hard to add information about relationships such as provenance.

Of course, this same simplicity (or even that it was simplistic) that reduced the expressivity of HTML compared with earlier hypertext is also the reasons for its success compared with earlier more heavy weight and usually centralised solutions.

However, Paul went on to describe how many of the features that were lost have re-emerged in plugins, server enhancements (this made me think of systems such as zLinks, which start to add an element of external linkage). I wasn’t totally convinced as these features are still largely in research prototypes and not entered the mainstream, but it made a good end to the story!

demos and documentation

There was a demo session as well as some short demos as part of talks. Lots’s of interesting ideas. One that particularly caught my eye (although not incredibly webby) was Ana Nelson‘s documentation generator “dexy” (not to be confused with doxygen, another documentation generator). Dexy allows you to include code and output, including screen shots, in documentation (LaTeX, HTML, even Word if you work a little) and live updates the documentation as the code updates (at least updates the code and output, you need to change the words!). It seems to be both a test harness and multi-version documentation compiler all in one!

I recall that many years ago, while he was still at York, Harold Thimbleby was doing something a little similar when he was working on his C version of Knuth’s WEB literate programming system. Ana’s system is language neutral and takes advantage of recent developments, in particular the use of VMs to be able to test install scripts and to be sure to run code in a consistent environments. Also it can use browser automation for web docs — very cool 🙂

Relating back to Paul’s keynote this is exactly an example of Nelson’s transclusion — the code and outputs included in the document but still tied to their original source.

And on this same theme I demoed Snip!t as an example of both:

  1. attempting to bookmark parts of web pages, a form of transclusion
  2. using data detectors a form of external linkage

Another talk/demo also showed how Compendium could be used to annotate video (in the talk regarding fashion design) and build rationale around … yet another example of external linkage in action.

… and when looking after the event at some of Weigang Wang‘s work on collaborative hypermedia it was pleasing to see that it uses a theoretical framework for shared understanding in collaboratuve hypermedia that builds upon my own CSCW framework from the early 1990s 🙂

sessions: narrative, creativity and the absurd

Impossible to capture in a few words, but one session included different talks and discussion about the relation of narrative and various forms of web experiences — including a talk on the cognitive psychology of the Kafkaesque. Also discussion of creativity with Nathan live recording in IBIS!

what is web science

I guess inevitably in a new area there was some discussion about “what is web science” and even “is web science a discipline”. I recall similar discussions about the nature of HCI 25 years ago and not entirely resolved today … and, as an artist who was there reminded us, they still struggle with “what is art?”!

Whether or not there is a well defined discipline of ‘web science’, the web definitely throws up new issues for many disciplines including new challenges for computing in terms of scale, and new opportunities for the social sciences in terms of intrinsically documented social interactions. One of the themes that recurred to distinguish web science from simply web technology is the human element — joy to my ears of course as a HCI man, but I think maybe not the whole story.

Certainly the gathering of people from different backgrounds in a sort of disciplinary bohemia is exciting whether or not it has a definition.

  1. see also “Names, URIs and why the web discards 50 years of computing experience“[back]
  2. Wendy Hall, Hugh Davis and Gerard Hutchings, “Rethinking Hypermedia:: The Microcosm Approach, Springer, 1996.[back]
  3. Spreading activation is used by a number of people, some of my own work with others at Athens, Rome and Talis is reported in “Ontologies and the Brain: Using Spreading Activation through Ontologies to Support Personal Interaction” and “Spreading Activation Over Ontology-Based Resources: From Personal Context To Web Scale Reasoning“.[back]

Names, URIs and why the web discards 50 years of computing experience

Posted on by

Names and naming have always been a big issue both in computer science and philosophy, and a topic I have posted on before (see “names – a file by any other name“).

In computer science, and in particular programming languages, a whole vocabulary has arisen to talk about names: scope, binding, referential transparency. As in philosophy, it is typically the association between a name and its ‘meaning’ that is of interest. Names and words, whether in programming languages or day-to-day language, are, what philosophers call, ‘intentional‘: they refer to something else. In computer science the ‘something else’ is typically some data or code or a placeholder/variable containing data or code, and the key question of semantics or ‘meaning’ is about how to identify which variable, function or piece of data a name refers to in a particular context at a particular time.

The emphasis in computing has tended to be about:

(a) Making sure names have unambiguous meaning when looking locally inside code. Concerns such as referential transparency, avoiding dynamic binding and the deprecation of global variables are about this.

(b) Putting boundaries on where names can be seen/understood, both as a means to ensure (a) and also as part of encapsulation of semantics in object-based languages and abstract data types.

However, there has always been a tension between clarity of intention (in both the normal and philosophical sense) and abstraction/reuse. If names are totally unambiguous then it becomes impossible to say general things. Without a level of controlled ambiguity in language a legal statement such as “if a driver exceeds the speed limit they will be fined” would need to be stated separately for every citizen. Similarly in computing when we write:

function f(x) { return (x+1)*(x-1); }

The meaning of x is different when we use it in ‘f(2)’ or ‘f(3)’ and must be so to allow ‘f’ to be used generically. Crucially there is no internal ambiguity, the two ‘x’s refer to the same thing in a particular invocation of ‘f’, but the precise meaning of ‘x’ for each invocation is achieved by external binding (the argument list ‘(2)’).

Come the web and URLs and URIs.

Fiona@lovefibre was recently making a test copy of a website built using WordPress. In a pure html website, this is easy (so long as you have used relative or site-relative links within the site), you just copy the files and put them in the new location and they work 🙂 Occasionally a more dynamic site does need to know its global name (URL), for example if you want to send a link in an email, but this can usually be achieved using configuration file. For example, there is a development version of Snip!t at cardiff.snip!t.org (rather then www.snipit.org), and there is just one configuration file that needs to be changed between this test site and the live one.

Similarly in a pristine WordPress install there is just such a configuration file and one or two database entries. However, as soon as it has been used to create a site, the database content becomes filled with URLs. Some are in clear locations, but many are embedded within HTML fields or serialised plugin options. Copying and moving the database requires a series of SQL updates with string replacements matching the old site name and replacing it with the new — both tedious and needing extreme care not to corrupt the database in the process.

Is this just a case of WordPress being poorly engineered?

In fact I feel more a problem endemic in the web and driven largely by the URL.

Recently I was experimenting with Firefox extensions. Being a good 21st century programmer I simply found an existing extension that was roughly similar to what I was after and started to alter it. First of course I changed its name and then found I needed to make changes through pretty much every file in the extension as the knowledge of the extension name seemed to permeate to the lowest level of the code. To be fair XUL has mechanisms to achieve a level of encapsulation introducing local URIs through the ‘chrome:’ naming scheme and having been through the process once. I maybe understand a bit better how to design extensions to make them less reliant on the external name, and also which names need to be changed and which are more like the ‘x’ in the ‘f(x)’ example. However, despite this, the experience was so different to the levels of encapsulation I have learnt to take for granted in traditional programming.

Much of the trouble resides with the URL. Going back to the two issues of naming, the URL focuses strongly on (a) making the name unambiguous by having a single universal namespace;  URLs are a bit like saying “let’s not just refer to ‘Alan’, but ‘the person with UK National Insurance Number XXXX’ so we know precisely who we are talking about”. Of course this focus on uniqueness of naming has a consequential impact on generality and abstraction. There are many visitors on Tiree over the summer and maybe one day I meet one at the shop and then a few days later pass the same person out walking; I don’t need to know the persons NI number or URL in order to say it was the same person.

Back to Snip!t, over the summer I spent some time working on the XML-based extension mechanism. As soon as these became even slightly complex I found URLs sneaking in, just like the WordPress database 🙁 The use of namespaces in the XML file can reduce this by at least limiting full URLs to the XML header, but, still, embedded in every XML file are un-abstracted references … and my pride in keeping the test site and live site near identical was severely dented1.

In the years when the web was coming into being the Hypertext community had been reflecting on more than 30 years of practical experience, embodied particularly in the Dexter Model2. The Dexter model and some systems, such as Wendy Hall’s Microcosm3, incorporated external linkage; that is, the body of content had marked hot spots, but the association of these hot spots to other resources was in a separate external layer.

Sadly HTML opted for internal links in anchor and image tags in order to make html files self-contained, a pattern replicated across web technologies such as XML and RDF. At a practical level this is (i) why it is hard to have a single anchor link to multiple things, as was common in early Hypertext systems such as Intermedia, and (ii), as Fiona found, a real pain for maintenance!

  1. I actually resolved this by a nasty ‘hack’ of having internal functions alias the full site name when encountered and treating them as if they refer to the test site — very cludgy![back]
  2. Halasz, F. and Schwartz, M. 1994. The Dexter hypertext reference model. Commun. ACM 37, 2 (Feb. 1994), 30-39. DOI= http://doi.acm.org/10.1145/175235.175237[back]
  3. Hall, W., Davis, H., and Hutchings, G. 1996 Rethinking Hypermedia: the Microcosm Approach. Kluwer Academic Publishers.[back]

Italian conferences: PPD10, AVI2010 and Search Computing

Posted on by

I got back from trip to Rome and Milan last Tuesday, this included the PPD10 workshop that Aaron, Lucia, Sri and I had organised, and the AVI 2008 conference, both in University of Rome “La Sapienza”, and a day workshop on Search Computing at Milan Polytechnic.

PPD10

The PPD10 workshop on Coupled Display Visual Interfaces1 followed on from a previous event, PPD08 at AVI 2008 and also a workshop on “Designing And Evaluating Mobile Phone-Based Interaction With Public Displays” at CHI2008.  The linking of public and private displays is something I’ve been interested in for some years and it was exciting to see some of the kinds of scenarios discussed at Lancaster as potential futures some years ago now being implemented over a range of technologies.  Many of the key issues and problems proposed then are still to be resolved and new ones arising, but certainly it seems the technology is ‘coming of age’.  As well as much work filling in the space of interactions, there were also papers that pushed some of the existing dimensions/classifications, in particular, Rasmus Gude’s paper on “Digital Hospitality” stretched the public/private dimension by considering the appropriation of technology in the home by house guests.  The full proceedings are available at the PPD10 website.

AVI 2010

AVI is always a joy, and AVI 2010 no exception; a biennial, single-track conference with high-quality papers (20% accept rate this year), and always in lovely places in Italy with good food and good company!  I first went to AVI in 1996 when it was in Gubbio to give a keynote “Closing the Loop: modelling action, perception and information“, and have gone every time since — I always say that Stefano Levialdi is a bit like a drug pusher, the first experience for free and ever after you are hooked! The high spot this year was undoubtedly Hitomi Tsujita‘s “Complete fashion coordinator”2, a system for using social networking to help choose clothes to wear — partly just fun with a wonderful video, but also a very thoughtful mix of physical and digital technology.


images from Complete Fashion Coordinator

The keynotes were all great, Daniel Keim gave a really lucid state of the art in Visual Analytics (more later) and Patrick Lynch a fresh view of visual understanding based on many years experience and highlighting particularly on some of the more immediate ‘gut’ reactions we have to interfaces.  Daniel Wigdor gave an almost blow-by-blow account of work at Microsoft on developing interaction methods for next-generation touch-based user interfaces.  His paper is a great methodological exemplar for researchers combining very practical considerations, more principled design space analysis and targeted experimentation.

Looking more at the detail of Daniel’s work at Microsoft, it is interesting that he has a harder job than Apple’s interaction developers.  While Apple can design the hardware and interaction together, MS as system providers need to deal with very diverse hardware, leading to a ‘least common denominator’ approach at the level of quite basic touch interactions.  For walk-up-and use systems such as Microsoft Surface in bar tables, this means that users have a consistent experience across devices.  However, I did wonder whether this approach which is basically the presentation/lexical level of Seeheim was best, or whether it would be better to settle at some higher-level primitives more at the Seeheim dialog level, thinking particularly of the way the iPhone turns pull down menus form web pages into spinning selectors.  For devices that people own it maybe that these more device specific variants of common logical interactions allow a richer user experience.

The complete AVI 2010 proceedings (in colour or B&W) can be found at the conference website.

The very last session of AVI was a panel I chaired on “Visual Analytics: people at the heart of data” with Daniel Keim, Margit Pohl, Bob Spence and Enrico Bertini (in the order they sat at the table!).  The panel was prompted largely because the EU VisMaster Coordinated Action is producing a roadmap document looking at future challenges for visual analytics research in Europe and elsewhere.  I had been worried that it could be a bit dead at 5pm on the last day of the conference, but it was a lively discussion … and Bob served well as the enthusiastic but also slightly sceptical outsider to VisMaster!

As I write this, there is still time (just, literally weeks!) for final input into the VisMaster roadmap and if you would like a draft I’ll be happy to send you a PDF and even happier if you give some feedback 🙂

Search Computing

I was invited to go to this one-day workshop and had the joy to travel up on the train from Rome with Stu Card and his daughter Gwyneth.

The search computing workshop was organised by the SeCo project. This is a large single-site project (around 25 people for 5 years) funded as one of the EU’s ‘IDEAS Advanced Grants’ supporting ‘investigation-driven frontier research’.  Really good to see the EU funding work at the bleeding edge as so many national and European projects end up being ‘safe’.

The term search computing was entirely new to me, although instantly brought several concepts to mind.  In fact the principle focus of SeCo is the bringing together of information in deep web resources including combining result rankings; in database terms a form of distributed join over heterogeneous data sources.

The work had many personal connections including work on concept classification using ODP data dating back to aQtive days as well as onCue itself and Snip!t.  It also has similarities with linked data in the semantic web word, however with crucial differences.  SeCo’s service approach uses meta-descriptions of the services to add semantics, whereas linked data in principle includes a degree of semantics in the RDF data.  Also the ‘join’ on services is on values and so uses a degree of run-time identity matching (Stu Card’s example was how to know that LA=’Los Angeles’), whereas linked data relies on URIs so (again in principle) matching has already been done during data preparation.  My feeling is that the linking of the two paradigms would be very powerful, and even for certain kinds of raw data, such as tables, external semantics seems sensible.

One of the real opportunities for both is to harness user interaction with data as an extra source of semantics.  For example, for the identity matching issue, if a user is linking two data sources and notices that ‘LA’ and ‘Los Angeles’ are not identified, this can be added as part of the interaction to serve the user’s own purposes at that time, but by so doing adding a special case that can be used for the benefit of future users.

While SeCo is predominantly focused on the search federation, the broader issue of using search as part of algorithmics is also fascinating.  Traditional algorithmics assumes that knowledge is basically in code or rules and is applied to data.  In contrast we are seeing the rise of web algorithmics where knowledge is garnered from vast volumes of data.  For example, Gianluca Demartini at the workshop mentioned that his group had used the Google suggest API to extend keywords and I’ve seen the same trick used previously3.  To some extent this is like classic techniques of information retrieval, but whereas IR is principally focused on a closed document set, here the document set is being used to establish knowledge that can be used elsewhere.  In work I’ve been involved with, both the concept classification and folksonomy mining with Alessio apply this same broad principle.

The slides from the workshop are appearing (but not all there yet!) at the workshop web page on the SeCo site.

  1. yes I know this doesn’t give ‘PPD’ this stands for “public and private displays”[back]
  2. Hitomi Tsujita, Koji Tsukada, Keisuke Kambara, Itiro Siio, Complete Fashion Coordinator: A support system for capturing and selecting daily clothes with social network, Proceedings of the Working Conference on Advanced Visual Interfaces (AVI2010), pp.127–132.[back]
  3. The Yahoo! Related Suggestions API offers a similar service.[back]

data types and interpretation in RDF

Posted on by

After following a link from one of Nad’s tweets, read Jeni Tennison’s “SPARQL & Visualisation Frustrations: RDF Datatyping“.  Jeni had been having problems processing RDF of MP’s expense claims, because the amounts were plain RDF strings rather than as typed numbers.  She  suggests some best practice rules for data types in RDF based on the underlying philosophy of RDF that it should be self-describing:

  • if the literal is XML, it should be an XML literal
  • if the literal is in a particular language (such as a description or a name), it should be a plain literal with that language
  • otherwise it should be given an appropriate datatype

These seem pretty sensible for simple data types.

In work on the TIM project with colleagues in Athens and Rome, we too had issues with representing data types in ontologies, but more to do with the status of a data type.  Is a date a single thing “2009-08-03T10:23+01:00″, or is it a compound [[date year=”2009″ month=”8” …]]?

I just took a quick peek at how Dublin Core handles dates and see that the closest to standard references1 still include dates as ‘bare’ strings with implied semantics only, although one of the most recent docs does say:

“It is recommended that RDF applications use explicit rdf:type triples …”

and David MComb’s “An OWL version of the Dublin Core” gives an alternative OWL ontology for DC that does include an explicit type for dc:date:

<owl:DatatypeProperty rdf:about="#date">
  <rdfs:domain rdf:resource="#Document"/>
  <rdfs:range rdf:resource="http://www.w3.org/2001/XMLSchema#dateTime"/>
</owl:DatatypeProperty>

Our solution to the compound types has been to have “value classes” which do not represent ‘things’ in the world, similar to the way the RDF for vcard represents  complex elements such as names using blank nodes:

<vCard:N rdf:parseType="Resource">
  <vCard:Family> Crystal </vCard:Family>
  <vCard:Given> Corky </vCard:Given>
  ...
</vCard:N>

From2

This is fine, and we can have rules for parsing and formatting dates as compound objects to and from, say, W3C datetime strings.  However, this conflicts with the desire to have self-describing RDF as these formatting and parsing rules have to be available to any application or be present as reasoning rules in RDF stores.  If Jeni had been trying to use RDF data coded like this she would be cursing us!

This tension between representations of things (dates, names) and more semantic descriptions is also evident in other areas.  Looking again at Dublin Core the metamodal allows a property such as “subject”  to have a complex object with a URI and possibly several string values.

Very semantic, but hardly mashes well with sources that just say <dc:subject>Biology</dc:subject>.  Again a reasoning store could infer one from the other, but we still have issues about where the knowledge for such transformations resides.

Part of the problem is that the ‘self-describing’ nature of RDF is a bit illusary.   In (Piercian) semiotics the interpretant of a sign is crucial, representations are interpreted by an agent in a particular context assuming a particular language, etc.  We do not expect human language to be ‘sef describing’ in the sense of being totally acontextual.  Similarly in philosophy words and ideas are treated as intentional, in the (not standard English) sense that they refer out to something else; however, the binding of the idea to the thing it refers to is not part of the word, but separate from it.  Effectively the desire to be self-describing runs the risk of ignoring this distinction3.

Leigh Dodds commented on Jeni’s post to explain that the reason the expense amounts were not numbers was that some were published in non-standard ways such as “12345 (2004)”.  As an example this captures succinctly the perpetual problem between representation and abstracted meaning.  If a journal article was printed in the “Autumn 2007” issue of  quarterly magazine, do we express this as <dc:date>2007</dc:date> or <dc:date>2007-10-01</dc:date>  attempting to give an approximation or inference from the actual represented date.

This makes one wonder whether what is really needed here is a meta-description of the RDF source (not simply the OWL as one wants to talk about the use of dc:date or whatever in a particular context) that can say things like “mainly numbers, but also occasionally non-strandard forms”, or “amounts sometimes refer to different years”.  Of course to be machine mashable there would need to be an ontology for such annotation …

  1. see “Expressing Simple Dublin Core in RDF/XML“, “Expressing Dublin Core metadata using HTML/XHTML meta and link elements” and Stanford DC OWL[back]
  2. Renato Iannella, Representing vCard Objects in RDF/XML, W3C Note, 22 February 2001.[back]
  3. Doing a quick web seek, these issues are discussed in several places, for example: Glaser, H., Lewy, T., Millard, I. and Dowling, B. (2007) On Coreference and the Semantic Web, (Technical Report, Electronics & Computer Science, University of Southampton) and Legg, C. (2007). Peirce, meaning and the semantic web (Paper presented at Applying Peirce Conference, University of Helsinki, Finland, June 2007). [back]

the more things change …

Posted on by

I’ve been reading Jeni (Tennison)’s Musings about techie web stuff XML, RDF, etc.  Two articles particularly caught my eye.  One was Versioning URIs about URIs for real world and conceptual objects (schools, towns), and in particular how to deal with the fact that these change over time.  The other was Working With Fragmented Overlapping Markup all about managing multiple hierarchies of structure for the same underlying data.

In the past I’ve studied issues both of versioning and of multiple structures on the same data1, and Jeni lays out the issues for both really clearly. However, both topics gave a sense of deja vu, not just because of my own work, but because they reminded me of similar issues that go way back before the web was even thought of.

Versioning URIs and unique identifiers2

In my very first computing job (COBOL programming for Cumbria County Council) many many years ago, I read an article in Computer Weekly about choice of keys (I think for ISAM not even relational DBs). The article argued that keys should NEVER contain anything informational as it is bound to change. The author gave an example of standard maritime identifiers for a ship’s journey (rather like a flight number) that were based on destination port and supposed to never change … except when the ship maybe moved to a different route. There is always an ‘except’, so, the author argued, keys should be non-informational.

Just a short while after reading this I was working on a personnel system for the Education Dept. and was told emphatically that every teacher had a DES code given to them by government and that this code never changed. I believed them … they were my clients. However, sure enough, after several rounds of testing and demoing when they were happy with everything I tried a first mass import from the council’s main payroll file. Validations failed on a number of the DES numbers. It turned out that every teacher had a DES number except for new teachers where the Education Dept. then issued a sort of ‘pretend’ one … and of course the DES number never changed except when the real number came through. Of course, the uniqueness of the key was core to lots of the system … major rewrite :-/

The same issues occurred in many relational DBs where the spirit (rather like RDF triples) was that the record was defined by values, not by identity … but look at most SQL DBs today and everywhere you see unique but arbitrary identifying ids. DOIs, ISBNs, the BBC programme ids – we relearn the old lessons.

Unfortunately, once one leaves the engineered world of databases or SemWeb, neither arbitrary ids nor versioned ones entirely solve things as many real world entities tend to evolve rather than metamorphose, so for many purposes http://persons.org/2009/AlanDix is the same as http://persons.org/1969/AlanDix, but for others different: ‘nearly same as’ only has limited transitivity!

  1. e.g. Modelling Versions in Collaborative Work and Collaboration on different document processing platforms; quite a few years ago now![back]
  2. edited version of comments I left on Jeni’s post[back]

going SIOC (Semantically-Interlinked Online Communities)

Posted on by

I’ve just SIOC enabled this blog using the SIOC Exporter for WordPress by Uldis Bojars.  Quoting from the SIOC project web site:

The SIOC initiative (Semantically-Interlinked Online Communities) aims to enable the integration of online community information. SIOC provides a Semantic Web ontology for representing rich data from the Social Web in RDF.

This means you can explore the blog as an RDF Graph including this post.

<sioc:Post rdf:about="http://www.alandix.com/blog/?p=176">
    <sioc:link rdf:resource="http://www.alandix.com/blog/?p=176"/>
    <sioc:has_container rdf:resource="http://www.alandix.com/blog/index.php?sioc_type=site#weblog"/>
    <dc:title>going SIOC (Semantically-Interlinked Online Communities)</dc:title>
    <sioc:has_creator>
        <sioc:User rdf:about="http://www.alandix.com/blog/author/admin/" rdfs:label="alan">
            <rdfs:seeAlso rdf:resource="http://www.alandix.com/blog/index.php?sioc_type=user&amp;sioc_id=1"/>
        </sioc:User>
    </sioc:has_creator>
...

RDF sequences … could they be more semantic?

Posted on by

Although triples can in principle express anything (well anything computational), this does not mean they are particularly appropriate for everything1.

RDF sequences are one of the most basic structured types and I have always found the use of rdf:_1, rdf:_2 at best clunky.  In particular I don’t like the fact that the textual form embodies the meaning.

In the RDF schema, rdf:_1, rdf:_2, etc are all instances of the class rdfs:ContainerMembershipProperty and sub-properties of rdfs:member.  However, I was also looking to see if there was some (implicitly defined) property of each of them that said which index they represented.  For example:

<rdf:_3> <rdf:isSequenceNumber> “3”

This would mean that the fact that rdf:_3 corresponded to the third element in a sequence was expressed semantically by rdf:isSequenceNumber as well as lexically in the label “_3”.

Sadly I could find no mention of this or any alternative technique to give the rdf:_nnn properties explicit semantics 🙁

This is not just me being a purist,  having explicit semantics makes it possible to express queries such as gathering together contiguous pairs in a sequence:

<ex:a> ?r1 ?a.
<ex:a> ?r2 ?b.
?r1 <rdf:hasSequenceNumber> ?index.
?r2 <rdf:hasSequenceNumber> ?index + 1.

Without explicit semantics, this would need to be expressed using string concatenation to create the labels for the relations – yuck!

Have I missed something? Is there an alternative mechanism in the RDF world that is like this or better?

Mind you I don’t see what’s wrong with a[index] … but may be that is just too simple?

  1. see also previous posts on “It-ness and identity: FOAF, RDF and RDMS” and “digging ourselves back from the Semantic Web mire“[back]

web of data practioner’s days

Posted on by

I am at the Web of Data Practitioners Days (WOD-PD 2008) in Vienna.  Mixture of talks and guided hands-on sessions.  I presented first half of session on “Using the Web of Data” this morning with focus (surprise) on the end user. Learnt loads about some of the applications out there – in fact Richard Cyganiak .  Interesting talk from a guy at the BBC about the way they are using RDF to link the currently disconnected parts of their web and also archives.  Jana Herwig from Semantic Web Company has been live blogging the event.

Being here has made me think about the different elements of SemWeb technology and how they individually contribute to the ‘vision’ of Linked Data.  The aim is to be able to link different data sources together.  For this having some form of shared/public vocabulary or ‘data definitions’ is essential as is some relatively uniform way of accessing data.  However, the implementation using RDF or use of SPARQL etc. seems to be secondary and useful for some data, but not other forms of data where tabular data may be more appropriate.  Linking these different representations  together seems far more important than specific internal representations.  So wondering whether there is a route to linked data that allows a more flexible interaction with existing data and applications as well as ‘sucking’ in this data into the SemWeb.  Can the vocabularies generated for SemWeb be used as meta information for other forms of information and can  query/access protocols be designed that leverage this, but include broader range of data types.

It-ness and identity: FOAF, RDF and RDMS

Posted on by

Issues of ‘sameness’ are the underpinnings of any common understanding; if I talk about America, bananas or Caruso, we need to know we are talking about the ‘same’ thing.

Codd’s relational calculus was unashamedly phenomenological – if two things have the same attributes they are the same. Of course in practice, we often have things which look the same and yet we know are different: two cans of beans, two employees called David Jones. So many practical SQL database designs use unique ids as the key field of a table effectively making sure that otherwise identical rows are distinct1.

The id gives a database record identity – it is a something independent of its attributes.

I usually call this quality ‘it-ness’ and struggled to find appropriate (probably German) philosophical term to refer to it. Before we can point at something and say ‘it is a chair’, it must be an ‘it’ something we can refer to. This it-ness must be there before we consider the proeprties of ‘ot’ (legs, seat, etc.). It-ness is related to the substance/accident distinction important in medieval scholastic debate on transubstantiation, but different as the bread needs to be an ‘it’ before we can say that its real nature (substance) is different from its apparent nature (accidents).

In contrast RDF takes identity, as embodied in a URI, as its starting point. The origins of RDF are in web meta-data – talking about web pages … that is RDF is about talking about something else, and that something else has some form of (unique) identity. Although the word ‘ontology’ seems to be misused almost beyond recognition in computer science, here we are talking about true ontology. RDF assumes as a starting point it is discussing things that are, that exist, that have being. Given this of course several distinct things may have similar attributes2.

Whilst RDMS have problems talking about identity, and we often have to add artifices (like the id), to establish identity, in RDF the opposite problem arises. Often we do not have unique names even for web entities, and even less when we have RDF descriptions of people, places … or books. Nad discusses some of the problems of cleaning up book data (MARC, RDF and FRMR), part of which is establishing unique names … and really books are ‘easy’ as librarians have soent a long time thinking about idetifying them already.

FOAF (friend of a friend) is now widely used to represent personal relationships. In this WordPress blog, when I add blogroll entries it prompts for FOAF information: is this a work colleague, family, friend (but not foe or competitor … FOAF is definitely about being friendly!).

FOAF has an RDF format, but examples, both in practice … and in the XMLNS RDF specification, are not full of “rdf:about” links as are typical RDF documents. This is because, while people clearly do have unique identity, there is thankfully no URI scheme that uniquely and universally defies us3.

In practice FOAF says things like “there is a person whose name is John Doe”, or “the blog VirtualChaos is by a person who is a friend and colleague of the author of this blog”.

In terms of identity this is a blank node “the person who …”. The computational representation of the person is a placeholder, or a variable waiting to be associated with other placeholders.

In terms of phenomenological attributes, the values either do not uniquely identify an individual (here may be many John Doe’s) and the individual may have several potential values for a given attribute (John Doe may not be the body’s only name,and a person may have several email addresses).

In order to match individuals in FOAF, we typically need to make assumption: while I may have several email addresses, they are all personal, so if two people have the same email address they are the same person. Of course such reasoning is defeasible: some families share an email address, but serves as a way of performing partial and approximate matching.

I think to the semantic web purist the goal would be to have the unique personal URI. However, to my mind the incomplete, often vague and personally defined FOAF is closer to the way the real world works even when ontologically there is a unique entity in the world that is the subject. FOAF challenges simplistic assumptions and representations of both a phenomenological and ontological nature.

  1. Furthermore if you do not specify a key, RDMS are likely to treat a relation as bag rather than a set of tuples! Try inserting the same record twice.[back]
  2. For those who know their quantum mechanics RDMS records are like Fermions and obey Pauli exclusion principle, whilst RDF entities are like Bosons and several entities can exist with identical attributes.[back]
  3. As it says in The Prisoner “I am not a number” … although maybe one day soon we will all be biometrically identified and have a global URI :-/[back]

practical RDF

Posted on by

I just came across D2RQ, a notation (plus implementation) for mapping relational databases to RDF, developed over the last four years by Chris Bizer, Richard Cyganiak and others at Freie Universität Berlin. In a previous post, “digging ourselves back from the Semantic Web mire“, I worried about the ghetto-like nature of RDF and the need for “abstractions that make non-triple structures more like the Semantic Web”, D2RQ is exactly the sort of thing, allowing existing relational databases to be accessed (but not updated) as if they were and RDF triple stores, including full SPARQL queries.

As D2RQ has clearly been around for years, I tried to do a bit of a web search to find things the other way around – more programmer-friendly layers on top of RDF (or XML) allowing it to be manipulated with IDL-like or other abstractions closer to ‘normal’ programming. ECMAScript for XML (E4X) seems to be just this allowing reasonably easy access to XML (but I guess RDF would be ‘flat’ in this). E4X has been around a few years (standard since 2005), but as far as I can see not yet in IE (surprise!). I guess for really practical XML it would be JSON, and there’s a nice discussion of different RDF in JSON representation issues on the n2 wiki “RDF JSON Brainstorming“. However, both E4X and RDF in JSON still are just accessing RDF nicely not adding higher level structure.

Going back to the beginning I was wondering about any tools that represent RDF as SQL / RDMS in order to make it available to ‘old technology’ … but then remembered that SPARQL creates tuples not triples so, I guess, one could say that is exactly what it does :-/