Posted on June 19th, 2009 7 commentsLinked Data and bibliographic metadata models
Some time after I wrote “UMR – Unified Metadata Resources“, I came across Chris Keene’s post “Linked data & RDF : draft notes for comment“, “just a list of links and notes” about Linked Data, RDF and the Semantic Web, put together to start collecting information about “a topic that will greatly impact on the Library / Information management world“.
While reading this post and working my way through the links on that page, I started realising that Linked Data is exactly what I tried to describe as One single web page as the single identifier of every book, author or subject. I did mention Semantic Web, URI’s and RDF, but the term “Linked Data” as a separate protocol had escaped me.
The concept of Linked Data was described by Tim Berners Lee, the inventor of the World Wide Web. Whereas the World Wide Web links documents (pages, files, images), which are basically resources about things, (“Information Resources” in Semantic Web terms), Linked Data (or the Semantic Web) links raw data and real life things (“Non-Information Resources”).
There are several definitions of Linked Data on the web, but here is my attempt to give a simple definition of it (loosely based on the definition in Structured Dynamics’ Linked Data FAQ):Linked Data is a methodology for providing relationships between things (data, concepts and documents) anywhere on the web, using URI’s for identifying, RDF for describing and HTTP for publishing these things and relationships, in a way that they can be interpreted and used by humans and software.
I will try to illustrate the different aspects using some examples from the library world. The article is rather long, because of the nature of the subject, then again the individual sections are a bit short. But I do supply a lot of links for further reading.
Data is relationships
The important thing is that “data is relationships“, as Tim Berners Lee says in his recent presentation for TED.
Before going into relationships between things, I have to point out the important distinction between abstract concepts and real life things, which are “manifestations” of the concepts. In Object modeling these are called “classes” (abstract concepts, types of things) and “objects” (real life things, or “instances” of “classes“).
- the class book can have the instances/objects “Cloud Atlas“, “Moby Dick“, etc.
- the class person can have the instances/objects “David Mitchell“, “Herman Melville“, etc.
In the Semantic Web/RDF model the concept of triples is used to describe a relationship between two things: subject – predicate – object, meaning: a thing has a relation to another thing, in the broadest sense:
- a book (subject) is written by (predicate) a person (object)
You can also reverse this relationship:
- a person (subject) is the author of (predicate) a book (object)
The person in question is only an author because of his or her relationship to the book. The same person can also be a mother of three children, an employee of a library, and a speaker at a conference.
Moreover, and this is important: there can be more than one relationship between the same two classes or types of things. A book (subject) can also be about (predicate) a person (object). In this case the person is a “subject” of the book, that can be described by a “keyword”, “subject heading”, or whatever term is used. A special case would be a book, written by someone about himself (an autobiography).
The problem with most legacy systems, and library catalogues as an example of these, is that a record for let’s say a book contains one or more fields for the author (or at best a link to an entry in an authority file or thesaurus), and separately one or more fields for subjects. This way it is not possible to see books written by an author and books about the same author in one view, without using all kinds of workarounds, link resolvers or mash-ups.
Using two different relationships that link to the same thing would provide for an actual view or representation of the real world situation.
Another important option of Linked Data/RDF: a certain thing can have as a property a link to a concept (or “class”) , describing the nature of the thing: “object Cloud Atlas” has type “book“; “object David Mitchell” has type “person“; “object Cloud Atlas” is written by “object David Mitchell“.
And of course, the property/relationship/predicate can also link to a concept describing the nature of the link.
Anywhere on the web
So far so good. But you may argue that this relationship theory is not very new. Absolutely right, but up until now this data-relationship concept has mainly been used with a view to the inside, focused on the area of the specific information system in question, because of the nature and the limitations of the available technology and infrastructure.
The “triple” model is of course exactly the same as the long standing methodology of Entity Relationship Diagrams (ERD), with which relationships between entities (=”classes“) are described. An ERD is typically used to generate a database that contains data in a specific information system. But ERD’s could just as well be used to describe Linked Data on the web.
Information systems, such as library catalogs, have been, and still are, for the greatest part closed containers of data, or “silos” without connections between them, as Tim Berners Lee also mentions in his TED presentation.
Lots of these silo systems are accessible with web interfaces, but this does not mean that items in these closed systems with dedicated web front ends can be linked to items in other databases or web pages. Of course these systems can have API‘s that allow system developers to create scripts to get related information from other systems and incorporate that external information in the search results of the calling system. This is what is being done in web 2.0 with so-called mash-ups.
But in this situation you need developers who know how to make scripts using specific scripting languages for all the different proprietary API’s that are being supported for all the individual systems.
If Linked Data was a global standard and all open and closed systems and websites supported RDF, then all these links would be available automatically to RDF enabled browser and client software, using SPARQL, the RDF Query Language.
- Linked Data/RDF can be regarded as a universal API.
The good thing about Linked Data is, that it is possible to use Linked Data mechanisms to link to legacy data in silo databases. You just need to provide an RDF wrapper for the legacy system, like has been done with the Library of Congress Subject Headings.
Some examples of available tools for exposing legacy data as RDF:
- Triplify – a web applications plugin that converts relational database structures into RDF triples
- D2R Server – a tool for publishing relational databases on the Semantic Web
- wp-RDFa – a wordpress plugin that adds some RDF information about Author and Title to WordPress blog posts
Of course, RDF that is generated like this will very probably only expose objects to link TO, not links to RDF objects external to the system.
Also, Linked Data can be used within legacy systems, for mixing legacy and RDF data, open and closed access data, etc. In this case we have RDF triples that have a subject URI from one data source and an object URI from another data source. In a situation with interlinked systems it would for instance be possible to see that the author of a specific book (data from a library catalog) is also speaking at a specific conference (data from a conference website). Objects linked together on the web using RDF triples are also known as an “RDF graph”. With RDF-aware client software it is possible to navigate through all the links to retrieve additional information about an object.
URI’s (“Uniform Resource Identifiers”) are necessary for uniquely identifying and linking to resources on the web. A URI is basically a string that identifies a thing or resource on the web. All “Information Resources”, or WWW pages, documents, etc. have a URI, which is commonly known as a URL (Uniform Resource Locator).
With Linked Data we are looking at identifying “Non-information Resources” or “real world objects” (people, concepts, things, even imaginary things), not web pages that contain information about these real world objects. But it is a little more complicated than that. In order to honour the requirement that a thing and its relations can be interpreted and used by humans and software, we need at least 3 different representations of one resource (see: How to publish Linked Data on the web):
- Resource identifier URI (identifies the real world object, the concept, as such)
- RDF document URI (a document readable for semantic web applications, containing the real world object’s RDF data and relationships with other objects)
- HTML document URI (a document readable for humans, with information about the real world object)
For instance, there could be a Resource Identifier URI for a book called “Cloud Atlas“. The web resource at that URI can redirect an RDF enabled browser to the RDF document URI, which contains RDF data describing the book and its properties and relationships. A normal HTML web browser would be redirected to the HTML document URI, for instance a web page about the book at the publisher’s website.
There are several methods of redirecting browsers and application to the required representation of the resource. See Cool URIs for the Semantic Web for technical details.
There are also RDF enabled browsers that transform RDF into web pages readable by humans, like the FireFox addon “Tabulator“, or the web based Disco and Marbles browsers, both hosted at the Free University Berlin.
RDF, vocabularies, ontologies
RDF or Resource Description Framework, is, like the name suggests, just a framework. It uses XML (or a simpler non-XML method N3) to describe resources by means of relationships. RDF can be implemented in vocabularies or ontologies, which are sets of RDF classes describing objects and relationships for a given field.
Basically, anybody can create an RDF vocabulary by publishing an RDF document defining the classes and properties of the vocabulary, at a URI on the web. The vocabulary can then be used in a resource by referring to the namespace (the URI) and the classes in that RDF document.
A nice and useful feature of RDF is that more than one vocabularies can be mixed and used in one resource.
Also, a vocabulary itself can reference other vocabularies and thereby inherit well established classes and properties from other RDF documents.
Another very useful feature of RDF is that objects can be linked to similar object resources describing the same real world thing. This way confusion about which object we are talking about, can be avoided.
A couple of existing and well used RDF vocabularies/ontologies:
- RDF – the base RDF vocabulary
- RDFS (for RDF Schema)
- DC (for Dublin Core)
- FOAF (for FOAF- Friend of a Friend) – online identities and social networks
- SKOS (for SKOS – Simple Knowledge Organisation System) – thesauri, classification schemes, subject heading systems and taxonomies
- OWL (for OWL -Ontology Web Language)
(By the way, the links in the first column (to the RDF files themselves) may act as an illustration of the redirection mechanism described before. Some of them may link to either the RDF file with the vocabulary definition itself, or to a page about the vocabulary, depending on the type of browser you use: rdf-aware or not.)
A special case is:
<?xml version=”1.0″ encoding=”UTF-8″ ?>
- RDFa – a sort of microformat without a vocabulary of its own, which relies on other vocabularies for turning XHTML page attributes into RDF
<dc:publisher>Random House Trade Paperbacks</dc:publisher>
<dc:title>Cloud Atlas: A Novel</dc:title>
<rdfs:label>Cloud Atlas: A Novel</rdfs:label>
<rdfs:label>RDF document about the book: Cloud Atlas: A Novel</rdfs:label>
<rdfs:label>Review number 1 about: Cloud Atlas: A Novel</rdfs:label>
<rdfs:label>RDF Book Mashup</rdfs:label>
A partial view on this RDF file with the Marbles browser:
It seems obvious that Linked Data can be very useful in providing a generic infrastructure for linking data, metadata and objects, available in numerous types of data stores, in the online library world. With such a networked online data structure, it would be fairly easy to create all kinds of discovery interfaces for bibliographic data and objects. Moreover, it would also be possible to link to non-bibliographic data that might interest the users of these interfaces.
A brief and incomplete list of some library related Linked Data projects, some of which already mentioned above:
- RDF BookMashup – Integration of Web 2.0 data sources like Amazon, Google or Yahoo into the Semantic Web.
- Library of Congress Authorities – Exposing LoC Autorities and Vocabularies to the web using URI’s
- DBPedia – Exposing structured data from WikiPedia to the web
- LIBRIS – Linked Data interface to Swedish LIBRIS Union catalog
- Scriblio+Wordpress+Triplify – “A social, semantic OPAC Union Catalogue”
And what about MARC, AACR2 and RDA? Is there a role for them in the Linked Data environment? RDA is supposed to be the successor of AACR2 as a content standard that can be used with MARC, but also with other encoding standards like MODS or Dublin Core.
The RDA Entity Relationship Diagram, that incorporates FRBR as well, can of course easily be implemented as an RDF vocabulary, that could be used to create a universal Linked Data library network. It really does not matter what kind of internal data format the connected systems use.
Posted on April 27th, 2009 1 comment
In my post “Tweeting Libraries” among other things I described my Personal Twitter experience as opposed to Institutional Twitter use. Since then I have discovered some new developments in my own Twitter behaviour and some trends in Twitter at large: individual versus social.
There have been some discussions on the web about the pros and cons and the benefits and dangers of social networking tools like Twitter, focusing on “noise” (uninteresting trivial announcements) versus “signal” (meaningful content), but also on the risk of web 2.0 being about digital feudalism, and being a possible vehicle for fascism (as argumented by Andrew Keen).
My kids say: “Twitter is for old people who think they’re cool“. According to them it’s nothing more than : “Just woke up; SEND”, “Having breakfast; SEND”; “Drinking coffee; SEND”; “Writing tweet; SEND”. For them Twitter is only about broadcasting trivialities, narcissistic exhibitionism, “noise”.
For their own web communications they use chat (MSN/Messenger), SMS (mobile phone text messages), communities (Hyves, the Dutch counterpart of MySpace) and email. Basically I think young kids communicate online only within their groups of friends, with people they know.
Just to get an overview: a tweet, or Twitter message, can basically be of three different types:
- just plain messages, announcements
- replies: reactions to tweets from others, characterised by the “@<twittername>” string
- retweets: forwarding tweets from others, characterised by the letters “RT“
Although a lot of people use Twitter in the “exhibitionist” way, I don’t do that myself at all. If I look at my Twitter behaviour of the past weeks, I almost only see “retweets” and “replies”.
Both “replies” and “retweets” obviously were not features of the original Twitter concept, they came into being because Twitter users needed conversation.
A reply is becoming more and more a replacement for short emails or mobile phone text messages, at least for me. These Twitter replies are not “monologues”, but “dialogues”. If you don’t want everybody to read these, you can use a “Direct message” or “DM“.
Retweets are used to forward interesting messages to the people who are following you, your “community” so to speak. No monologue, no dialogue, but sharing information with specific groups.
The “@<twittername>” mechanism is also used to refer to another Twitter user in a tweet. In official Twitter terminology “replies” have been replaced by “mentions“.
Retweets and replies are the building blocks of Twitter communities. My primary community consists of people and organisations related to libraries. Just a small number of these people I actually know in person. Most of them I have never met. The advantage of Twitter here is obvious: I get to know more people who are active in my professional area, I stay informed and up to date, I can discuss topics. This is all about “signal”. If issues are too big for twitter (more than 140 characters) we can use our blogs.
But it’s not only retweets and replies that make Twitter communities work. Trivialities (“noise”) are equally important. They make you get to know people and in this way help create relationships built on trust.
Another compelling example of a very positive social use of Twitter I experienced last week, when there were a number of very interesting Library 2.0 conferences, none of which I could attend in person because of our ILS project:
- ELAG 2009 (European Library Automation Group) in Bratislava, April 22-24
- Dutch Conference Social Networks 2009 in Rotterdam, April 22
- Ugame Ulearn 2009 in Delft, April 23
All of these conferences were covered on Twitter by attendees using the hashtags #elag09, #csnr09 and #ugul09 . This phenomenon makes it possible for non-participants to follow all events and discussions at these conferences and even join in the discussions. Twitter at its best!
Twitter is just a tool, a means to communicate in many different ways. It can be used for good and for bad, and of course what is “good” and what is “bad” is up to the individual to decide.
Posted on March 30th, 2009 4 comments
Should libraries use Twitter ? Some web2.0 librarians think so, other people say it’s just a childish hype. Alice de Jong of the Peace Palace Library in The Hague wrote an article recently in the Dutch magazine Informatieprofessional (in Dutch), saying libraries should use Twitter as a means of quick and direct communication with their patrons. The Peace Palace Library uses Twitter as an automatic newsfeed .
An interesting question is: how can an in essence exhibitionist individual social networking tool be used in an institutional way?
What is Twitter anyway?
Wikipedia says: “Twitter is a social networking and micro-blogging service that enables its users to send and read other users’ updates known as tweets. Tweets are text-based posts of up to 140 bytes in length.” Basically a Twitter user broadcasts short messages to the web. Everybody can read these through that user’s personal Twitter page, or via an RSS feed on that page. Twitter users can subscribe to other Twitter users’ tweets by “following” them. In that case all followed tweets appear in their own Twitter stream. Twitter users can also reply to other tweets; this way it becomes a social networking environment. Tweets and replies are public, but there is also the option of “Direct messages”, that are private.
Twitter can be used via the Twitter website, or applications on mobile phones (Like Twitterfon ), on PC’s (like Tweetdeck ), or through widgets in other websites, like TwitterGadget in iGoogle .
Exhibitionism: that’s what Twitter originally is of course. Twitter asks “What are you doing?”. You simply tell the whole world (or world wide web at least) what you’re up to. A symptom of the egocentricity of this decade.
But somehow egocentric exhibitionism turned into professional cooperation and friendly conversation.
I first heard of Twitter at ELAG2008, less than a year ago. Besides the tag to be used for blog posts about the conference, there was also an announcement for a Twitter hashtag to be used. (And this at a conference where social tagging was promoted against controlled vocabularies!). There were a number of library bloggers there, who were also on Twitter: digicmb, Wowter, PatrickD.
Most people I follow or who are following me, are library people. Most of these also blog. So there is a kind of library2.0 community on Twitter, like there are all kinds of communities there. Some of my Twitter friends I know personally, I have met them, talked to them. Others I have only met on Twitter, but we do have agreeable, both professional and social talks. Remarkable: one of these Twitter friends I have never met “in the flesh”, is a colleague at the University of Amsterdam, but she works in the Medical Library, a long way from where I work.
My subjects on Twitter:
- football (soccer)
- what I am watching on TV – music
- what happens to me
- metadata issues
- day to day work issues
- my IGeLU stuff
- interesting blog posts
- my new blog posts (like this one!)
- interesting websites
- library 2.0 news
Twitter is also the “largest virtual expert helpdesk”, as digicmb recently experienced.
My personal Twitter experience is like having chats and discussions with colleagues at work, or with friends in a bar, but with a much larger group; or attending some library systems conference, with professional discussions, and also with social events, but then a continuous, intermittent one, and without travelling.
Now, how can an organisation, and in particular a library, use a tool, or rather a community, like Twitter for its own benefit?
Twitter has been around for three years, but it is growing incredibly fast. In The Netherlands politicians use Twitter, like our Foreign Secretary. Well known people in all areas are on Twitter, example: British writer Ben Okri started publishing his new poem “I Sing a New Freedom” on Twitter, one line a day. Newspapers write about it, popular TV shows talk about it.
So clearly, there is an ever growing audience. Libraries, as other organisations, should contact their audience where their audience is, so Twitter is another channel for communication.
Organisations can use Twitter as an alternative for news items on websites, RSS feeds, blogs, etc. But is there an advantage in using Twitter instead of other web2.0 channels? I am not sure. Just like surfing to websites and subscribing to RSS feeds, people have to actively start “following” an institutional Twitter account. Organisations, libraries need to actively promote their Twitter channel for it to be a success. But they also need to actively maintain their Twitter channel, just like all other web2.0 activities, otherwise it will just fade away, as Meredith Farkas notices in her blog post “It’s not all about the tech – why 2.0 tech fails“.
One advantage of using Twitter in libraries is the fact that it is getting beyond a hype. It will be one of the main channels of communication on the web.
Another one might be the interactive possibilities of Twitter. Institutional use of Twitter is mostly one way traffic, a broadcast to whoever wants to “follow”, as opposed to personal Twitter. See for instance the Library of Congress and the Peace Palace Library.
But as Alice de Jong points out, a number of libraries are choosing the “personal approach”. The tweeting librarian really communicates with patrons in order to promote closer contact between libaries and patrons.
This approach might also be a replacement for current libary chat services.
Personal institutional Twitter accounts could also be used as a means of representing the library as actual recognisable people, as has been promoted recently on a number of occasions. Patrons then will know library staff as experts in certain fields, instead of facing an anonymous organisation.
Conclusion: yes, libraries should use Twitter, as long as they can get a reasonable “following”, and have an official policy and staff dedicated to maintaining it.
Posted on February 4th, 2009 No comments
Jonathan Rochkind, in his post “How do name authorities work anyway?“, wonders if catalogers will confuse him with another writer of the same name that has an LC authority record, whereas he does not have one.
I guess the relevance of this problem depends entirely on the question: do you think it’s important to know that an author of a specific work is the same as the author of another work? A former colleague of mine whom I respect very much, used to say that it does not matter, as long as the correct name appears with the work in question. This was only six years ago, before the emergence of web 2.0 and library 2.0 type services. It is just like looking at a printed book: you read the author’s name, and if there is no further information on the back cover, or a list of publications by the author inside, then that’s all there is to it. In normal life, if you read a book or an article for pleasure, or even for business, study or research, that is no problem. No need for author authority records at all.
However, the picture is completely different from the point of view of the authors, especially in the case of professional scientific and research staff, where the exact number of publications and citations is crucial. For these authors it is vital that the correct authority record is used for their publications. Here we definitely need authority records with unique identifiers. But of course there are so many different systems in use: LC authority records , WorldCat Identities , national systems etc., they all use their own identifiers.
There is the proposal to develop the UAI, Universal Author Identifier . This system depends on authors registering and maintaining their own personal information in a freely accessible web based database. There was a pilot system for a while, but it is not clear if any results were reached.
In The Netherlands a similar project on a national scale has led to a live implementation: the DAI, Digital Author Identifier . The DAI is based on the identifier used for authors in the OCLC-PICA Dutch National Union Catalog /Common Catalog system “PPN”, and is assigned to every author who has been appointed to a position at a Dutch university or research institute or has some other relevant connection with one of these organisations. The DAI is used in the Dutch university repositories, the Dutch national Research Database and in the national integrated portal NARCIS .
The difference with UAI is that DAI is assigned by catalogers in one of the participating organisations, whereas UAI depends on voluntary cooperation of the authors themselves.
Of course a “universal author identifier” still does not solve Jonathan’s initial question: confusion is still possible if the authors do not have a clear interest in maintaining their information themselves.
Another issue here, about which something more can be said in a future post, is that for a real universal system we should use URI’s, as for unique works (see Owen Stephens’ post “The Future is Analogue “) and subject headings.