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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
http://kmr.nada.kth.se/el/ims/metadata.html
Overview
● Background● Abstract Models (RDF, DC, LOM)● Issues● Standard/Recommendation?
http://kmr.nada.kth.se/el/ims/metadata.html
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
http://kmr.nada.kth.se/el/ims/metadata.html
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
http://kmr.nada.kth.se/el/ims/metadata.html
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
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)
http://kmr.nada.kth.se/el/ims/metadata.html
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)
http://kmr.nada.kth.se/el/ims/metadata.html
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)
http://kmr.nada.kth.se/el/ims/metadata.html
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
http://kmr.nada.kth.se/el/ims/metadata.html
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.
http://kmr.nada.kth.se/el/ims/metadata.html
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>
http://kmr.nada.kth.se/el/ims/metadata.html
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.
http://kmr.nada.kth.se/el/ims/metadata.html
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.
http://kmr.nada.kth.se/el/ims/metadata.html
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
http://kmr.nada.kth.se/el/ims/metadata.html
DC Resource model
● Essentially resource – property – value – http://www.ukoln.ac.uk/metadata/dcmi/abstract-model/
http://kmr.nada.kth.se/el/ims/metadata.html
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.
http://kmr.nada.kth.se/el/ims/metadata.html
DC description Model
http://kmr.nada.kth.se/el/ims/metadata.html
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.
http://kmr.nada.kth.se/el/ims/metadata.html
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/
http://kmr.nada.kth.se/el/ims/metadata.html
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?
http://kmr.nada.kth.se/el/ims/metadata.html
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.
http://kmr.nada.kth.se/el/ims/metadata.html
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.
http://kmr.nada.kth.se/el/ims/metadata.html
Summary
● Abstract Model work closely related● Standard/Recommendation?● No XML in binding.