Simple Knowledge Organization System (SKOS) in the Context of Semantic Web Deployment, Library of Congress, May 2008

The Simple Knowledge Organization System (SKOS) in the context of Semantic Web Deployment Alistair Miles http://purl.org/net/aliman Library of Congress May 2008

THE FUTURE OF THE WEB http://purl.org/net/aliman

Testimony of Sir Timothy Berners-Lee CSAIL Decentralized Information Group Massachusetts Institute of Technology

Before the United States House of Representatives Committee on Energy and Commerce Subcommittee on Telecommunications and the Internet

http://dig.csail.mit.edu/2007/03/01-ushouse-future-of-the-web.html

http://purl.org/net/aliman

I. Foundations of the Web

“ The success of the World Wide Web, itself built on the open Internet, has depended on three critical factors:

unlimited links from any part of the Web to any other;

open technical standards as the basis for continued growth of innovation applications; and

separation of network layers , enabling independent innovation for network transport, routing and information applications.”

A. Universal linking: Anyone can connect to anyone...

“ In simple terms, the Web has grown because it's easy to write a Web page and easy to link to other pages.”

“ What makes it easy to create links ... is that there is no limit to the number of pages or number of links possible on the Web.”

“ Adding a Web page requires no coordination with any central authority , and has an extremely low, often zero, additional cost.”

“ Adding a page provides content, but adding a link provide the organization, structure and endorsement to information on the Web which turn the content as a whole into something of great value.”

“ The universality and flexibility of the Web's linking architecture has a unique capacity to break down boundaries of distance, language, and domains of knowledge.”

“ These traditional barriers fall away because the cost and complexity of a link is unaffected by most boundaries that divide other media.”

“ The Web's ability to allow people to forge links is why we refer to it as an abstract information space , rather than simply a network.”

II. Looking forward

“ First, the Web will get better and better at helping us to manage, integrate, and analyze data .”

“ Today, the Web is quite effective at helping us to publish and discover documents, but the individual information elements within those documents ... cannot be handled directly as data.”

“ Today you can see the data with your browser, but can't get other computer programs to manipulate or analyze it without going through a lot of manual effort yourself.”

“ As this problem is solved, we can expect that Web as a whole to look more like a large database or spreadsheet , rather than just a set of linked documents.”

A. Data Integration

“ Locked within all of this data is the key to knowledge about how to cure diseases, create business value, and govern our world more effectively.”

“ The good news is that a number of technical innovations...

... (RDF which is to data what HTML is to documents, and the Web Ontology Language (OWL) which allows us to express how data sources connect together) ...

... along with more openness in information sharing practices are moving the World Wide Web toward what we call the Semantic Web .”

“ Progress toward better data integration will happen through use of the key piece of technology that made the World Wide Web so successful: the link .”

“ The power of the Web today, including the ability to find the pages we're looking for , derives from the fact that documents are put on the Web in standard form, and then linked together .”

“ The Semantic Web will enable better data integration by allowing everyone who puts individual items of data on the Web to link them with other pieces of data using standard formats.”

DATA WEBS FOR E-SCIENCE http://purl.org/net/aliman

FlyWeb Project

Fruit flies ( Drosophila ...)

Model organism

Extensive body of genetic research

Much of that knowledge is in journal papers

Recognised value of research data

Establish public databases

E.g. FlyBase

Centrally curated

Data Webs

Link data resources

Ask questions that no single data resource can answer

What’s the easiest, cheapest, most scalable way to achieve this?

Agile approach, add value incrementally, return value early and often...

http://purl.org/net/aliman Vertical Web Apps Level 0 – Any Data Resources in the Web Level 1 – SPARQL End-points Level 2 – SPARQL End-points (Schema Alignment) Level 3 – SPARQL End-points (Integrated Data) Web 2 Mash-ups SPARQL Mash-ups SPARQL Mash-ups ??? Data Web Layer Cake

Example Application

[insert screenshot of mashup]

Future, self-publishing

As publishing data on the Web becomes easier...

...more research groups will publish their own data...

...rich network of data resources...

...challenging traditional view of scholarly life cycle & value chain ... value grid...

SKOS http://purl.org/net/aliman

Potted History

SKOS 2001 (pre-alpha)

Thesaurus Interchange Format (TIF), LIMBER Project

SKOS 2003 (alpha)

Semantic Web Advanced Development for Europe (SWAD-Europe)

SKOS 2005 (beta)

W3C Semantic Web Best Practices and Deployment Working Group (SWBPD)

SKOS 2008 (W3C Recommendation)

W3C Semantic Web Deployment Working Group (SWD)

http://purl.org/net/aliman http://www.w3.org/2007/Talks/1211-whit-tbl/

Layers in the Web

http://www.w3.org/2007/Talks/1211-whit-tbl/#(23)

Third layer is network (graph) of connections beyond documents...

... people, organisations, genes, proteins, concepts ...

Represent these connections (data) in the (Semantic) Web

KOS e.g. LCSH

Can be viewed as a network of interconnected concepts

Represent LCSH as data in the Web

Make those concepts and their interconnections part of the Web

Publishing KOS in the Web?

Use RDF

Basic framework for data in the Web – resources, literals, links... (“graphs” of data)

Publishing KOS in the Web?

Use SKOS

Standard set of...

Resource types (Classes)

Link types (Properties)

... For representing KOS as RDF data

(N.B. Because use URIS as names for classes and properties, call this an RDF vocabulary)

SKOS Resource Types (Classes)

skos:Concept

E.g. Baseball in art

skos:ConceptScheme

E.g. LCSH itself

SKOS Link Types (Properties)

For labeling concepts

skos:prefLabel, skos:altLabel, skos:hiddenLabel

For documenting concepts

skos:note, skos:scopeNote, skos:definition, skos:editorialNote...

For linking concepts

skos:broader, skos:narrower, skos:related

http://inkdroid.org/bzr/lcsh/docs/slides/

Publishing LCSH in the Web

Project LCSH into RDF (i.e. create an RDF representation)

Publish it in the Web as linked data

http://lcsh.info

Ed Summers, Clay Redding, Dan Krech, Antoine Isaac

Scope of SKOS

SKOS will be an all-encompassing standard for the lossless representation and exchange of all varieties of knowledge organisation system ... ?

No

http://lists.w3.org/Archives/Public/public-swd-wg/2008Feb/0116.html -- Antoine Isaac

“ ...the things that we aim at representing are very diverse: some classification schemes use ‘codes’ and refer to ‘classes’, thesauri have ‘terms’ and so on.”

“ Yet, it happens, looking at the way these things are used now and will be in the near future (with more and more links established between them), that (i) some standardisation has to take place, and that (ii) this standardisation can be actually grounded on some observed practical similarities ( http://www.w3.org/TR/skos-ucr/ )”

“ Our aim is not to replace the original objects in their initial context of use, but to allow to port them to a shared space , based on a simplified model , enabling wider re-use and better interoperability.”

Lessons from the Web

Less is more ...

E.g. REST over SOAP

SKOS should capture a small amount of common ground ... Just enough to enable KOS’s valuable concepts and connections to be deployed in the Web and be linked to/from

N.B. SKOS is infinitely extensible!

Easy to mix & match

Easy to refine

THE VALUE OF LINKS http://purl.org/net/aliman

The value of links

The Web showed, links between documents are really useful

Google’s pagerank showed, structure of network means something (and is worth something!)

Social networking Web sites showed, how much we value other kinds of links

Linked Metadata

You’ve got LCSH in the Web, what next?

... Linked metadata...?

http://inkdroid.org/bzr/lcsh/docs/slides/

[insert demo, show how links change topology of information space]

Value Proposition

Links are paths to the discovery of information

Links can be exploited in useful (and surprising) ways

Well-established KOS like LCSH can be hubs in the network of linked metadata, bridging ...

(On the Semantic Web, LCSH should get very high semantic pagerank !)

USING URIS http://purl.org/net/aliman

Why use URIs?

Identifier management

Data discovery

Identifier management

Referring to things

In a database, each table has a primary key

What happens when you try to combine data from 2 databases?

Identifier clashes (ambiguous reference)

Identifier aliases (co-reference)

Clashes hurt precision, give you nonsense

Aliases hurt recall, miss important results/links

URIs & identifier management

URIs are like a single, global pool of identifiers – one world-wide primary key

Can claim ownership of parts of “URI space”

Even though we’re all using same primary key, mechanism for avoiding URI clashes

Can join data from multiple sources with confidence

But ... doesn’t solve the alias problem, still need to find co-references

Data discovery

Problem with distributed data ... How do you find everything thats “out there”?

Two general approaches:

Centralised

Decentralised

Centralised discovery

Someone somewhere keeps a “catalogue” of everything

Everyone “knows” where that catalogue is

New sources “tell” the catalogue about themselves (a.k.a. “register” themselves)

E.g. Gas maintenance

Works well at small-medium scales

E.g. FlyWeb

Rely on networks outside the Web (e.g. Knowing the right people)

FlyWeb Project

[small number of large data resources]

Decentralised discovery

Data in one source refers data in another (using a URI)

Data from the other source can be retrieved directly, by “de-referencing” the URI via the Web

So given one data source, you can “follow your nose” and retrieve data from all linked sources ...

... without needing a central catalogue or registry, just the Web

Works well up to Web-scale

E.g. FOAF

Dereferenceable?

For some URIs, can retrieve a “representation” of the “resource” via the Web

(N.B. “resource” = “thing”)

FOAF

Very large number of relatively small data resources

Why use URIs?

Identity management

From 2 to 2 billion data sources, always a problem

Data discovery

Ability to “de-reference” a URI opens possibility for decentralisation

Ability to “de-reference” is also useful in centralised models (e.g. Registries can harvest)

SEMANTIC WEB DEPLOYMENT http://purl.org/net/aliman

W3C SWD WG

SKOS

RDFa

Recipes for publishing RDF (linked data)

Vocabulary management

W3C Semantic Web Activity

Semantic Web Deployment

Data Access (DAWG)

SPARQL query language, SPARQL protocol

GRDDL

OWL 2

SWHCLSIG

SWEO

SUMMARY http://purl.org/net/aliman

Suggestions

Linked KOS

Project LCSH into RDF (SKOS) – done

Publish LCSH as linked data in the Web – done

Publish SPARQL endpoint for LCSH

Linked metadata

Project LOC metadata into RDF

Publish LOC metadata as linked data in the Web

With links to LCSH & LCC

Publish SPARQL endpoint for LOC metadata

Bibliographic Information as RDF?

Projecting LCSH into RDF ... SKOS is standard vocabulary of resource & link types

Projecting LCSH metadata into RDF ... Which vocabulary to use???

Challenge – diversity of bibliographic information!

RDA -> RDF

Joint DCMI/RDA task force

Seed funding to develop initial prototype RDF vocabularies for bibliographic information

Based on FRBR and data model implicit in RDA

Early stages

http://dublincore.org/dcmirdataskgroup/

Karen Coyle

Thanks

STFC Rutherford Appleton Lab

Brian Matthews, Michael Wilson, Juan Bicarregui

Oxford Image Bioinformatics Research Group

David Shotton, Graham Klyne, Jun Zhao

W3C Semantic Web Deployment WG

Members of [email_address]

Comments on SKOS -> [email_address]

Simple Knowledge Organization System (SKOS) in the Context of Semantic Web Deployment, Library of Congress, May 2008

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