The LOM RDF binding – update 2004-01-28 Mikael Nilsson mini@[email protected] The Knowledge...

http://kmr.nada.kth.se/el/ims/metadata.html

The LOM RDF binding– update 2004-01-28

Mikael [email protected]

The Knowledge Management Research GroupCentre for user oriented IT design

Royal Institute of Technology, Stockholm

http://kmr.nada.kth.se


Overview

● Background● Abstract Models (RDF, DC, LOM)● Issues● Standard/Recommendation?


Background– Resource Description Framework

● XML – a general markup language– First W3C recommendation final in 1998– Roots in SGML and HTML

● RDF – a general metadata language– First W3C recommendation final in 1999– Roots in Descriptive Logic and databases


Background – RDF binding of LOM

● 2001: First draft in IMS Metadata 1.2– Work by KTH/Stockholm, L3S/Hannover,

WU/Vienna, within Edutella and UNIVERSAL● 2002: PAR accepted for LTSC

– Chair: Jon Mason– Second draft based on LOM 1.0

● 2003 – present:– Ballot-ready rewritten third draft in final stages


Background – binding features

● Reuses DC and Qualified DC vocabulary where appropriate– DC applications able to understand a LOM RDF record

partially, without transformation● Tries to leverage the flexibility of RDF

– Easy to combine with other standards / local extensions– Easy to combine several descriptions of the same

resource● See http://kmr.nada.kth.se/el/ims/metadata.html


Background – usage/participation

● The draft LOM RDF binding is is used in several projects– Swedish Educational Broadcasting Company (ur.se) –

online digital video archive– Swedish National Agency for Education (5-6 projects)– UK Curriculum Online metadata– UNIVERSAL/EducaNext brokerage platform– Edutella– LOM RSS module (Steven Downes)


Resource Description Framework

● Tim Berners-Lee's vision: A semantic web● Requirements on RDF:

– Metadata Framework (with certain built-in semantics)– Extensible (structurally, but also semantically)– Web-capable (unlike databases / AI systems)– Self-describing (machine semantics)


RDF: Structure

● An RDF description is a set of statements of the form (resource, property, value)

● Let's try to say “This book was written by Mark Twain”.

● A resource can be identified by a URI● A property is always identified by a URI● The value is another resource or a string.

(urn:isbn:1232-23-54-3, dc:creator, http://persons.org/Mark.Twain)


RDF: Structure (cont.)● This framework makes it easy to:

– Add new descriptions of the same resource.– Create new properties and use them.– Combine two separate descriptions of one of several

resources.● The result is often drawn as a graph:

urn:isbn:... http://persons.org/Mark.Twain

dc:creator

Mark Twain

vCard:FNdcclass:Date

1886

rdf:type

dc:created

rdf:value


Vocabularies

● RDF gives you a framework, a grammar. ● The “words” in the language are defined by

others (as with XML).● A vocabulary in the eyes of RDF is a set of URIs● Every URI must identify something well-defined

in the “world” (a thing, a concept, a property, etc.),

● i.e. the URIs must have semantics.


RDF Schema● W3C has also defined an RDF vocabulary that is

intended to be used to describe other RDF vocabularies (such as LOM or DC)!

● RDF Vocabulary Description Language 1.0, also known as RDF Schema.

● RDFS contains a base semantics that is used in alsmost all RDF descriptions. Expresses e.g.:– This resource is a Person <rdf:type>– Students are a kind of Persons <rdfs:subClassOf>– “dc:creator” is a Property <rdf:Property>


DC and RDF abstract models

● Both DC and RDF use aresource – property – value model

● DC has more high-level “values” than RDF– value URIs– value strings– rich values, etc.

● The LOM RDF binding uses the RDF model (of course)

● It also tries to be compatible with the DC model.


What's an Abstract Model?

● Framework for defining “metadata elements”● Query Languages need a framework

– Used in Edutella● Extensions of both semantic and structural nature● The LOM AM and DC AM have differences

=> This is being studied.● Two/Three models identified (maybe):

– Resource/Schema model and Instance model.


Creating an Annotation in LOM/RDF

1999-03-13

dcterms:W3CDTF

http://myresource.com/345345

lom-ann:Annotation

rdf:Alt

I thought blablabla en-US

Jag tyckte blablabla sv-SE

http://myresource.com/46675

●According to RDF, there are 4 descriptions in this record●According to DC, there are 2 descriptions (more advanced “value” concept)

Annotation descriptionResource description


DC Resource model

● Essentially resource – property – value – http://www.ukoln.ac.uk/metadata/dcmi/abstract-model/


DC Resource model

● Essence:– Each resource has zero or more properties.– Each property has one or more values.– Each value is a resource (so it can be further

described)● Example: a date can have a string representation, a

description, etc.


DC description Model


DC Description Model

● A description is made up of one or more statements about one, and only one, resource.

● Each statement is made up of– a property URI (a URI that identifies a property),– zero or one value URI (a URI that identifies a value of

the property), – zero or one encoding scheme URI (a URI that

identifies the class of the value), and– zero or more value representations of the value.


The Binding: status

● Includes text and RDF Schemas– Note: RDFS does not do validation!

● Work on the DC AM influences the binding– still not finalized

● General issues:– About schema or about instances?– What is conformance?

● Paper on the binding at ARIADNE conference 2003: http://kmr.nada.kth.se/papers/


The Binding: contents

● Conceptually, two things (recent insights):– A list of URIs, and their associated semantics.

● Can be partially encoded in an RDF Schema● Nothing related to constraints● This is 100% normative

– A specification of constraints for their use● Multiplicity, ordering, nesting, use of DC vocab, etc.● All the constraints of the schema● This part cannot be normative. Why?


The Binding

● Why cannot the constraints part be normative?– No control over record boundaries, orcombinations of

descriptions– Interferences with external vocabularies (DC, vCard)– In short: conformance is not well-defined.

● Possibilities:– One Standard, normative/informative parts– One Standard, One Recommended Practice– One Recommended practice.


The Binding: misc

● Note that there are two RDF specs:– Concepts and abstract syntax– RDF/XML syntax

● The binding will not use XML RDF syntax, only graphs, and maybe a notation called N3, (used for RDF testcases).– Unfortunately, the RDF/XML syntax is confusing

both for RDFers and non-RDFers.


Summary

● Abstract Model work closely related● Standard/Recommendation?● No XML in binding.

The LOM RDF binding – update 2004-01-28 Mikael Nilsson mini@[email protected] The Knowledge...

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