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Feb
20
07
Andy Powell, Eduserv [email protected]
www.eduserv.org.uk/foundation
The Dublin Core Abstract Model – a packaging standard?
Content Packaging for Complex Objects: Technical Workshop
flickr photo by amalthya
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Feb 2007Content Packaging for Complex Objects: Technical Workshop 2
Why Dublin Core?
• well… maybe…
this workshop is about content packaging not metadata!?
DC is just 15 elements for describing Web pages isn’t it?
DC doesn’t do content packaging does it?
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Feb 2007Content Packaging for Complex Objects: Technical Workshop 3
DC and content packaging
• this talk is about the DCMI Abstract Model…
• …and its relationship to content packaging
• it is not intended as a tutorial
• but I appreciate that the DCMI Abstract Model is new to many of you
• I will therefore start by summarising the background, context and main features of the DCAM
• then I’ll give some examples
• and finally try to draw some conclusions
http://dublincore.org/documents/abstract-model/
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Feb 2007Content Packaging for Complex Objects: Technical Workshop 4
DCMI Abstract Model background
• in the early days of Dublin Core there was no explicit model associated with DC metadata descriptions
• there were implicit models and conventional wisdom…
– largely ‘flat’ in nature – i.e. a set of metadata elements describing a single thing (e.g. a Web page)
• and there were known problems…– like sometimes it was obvious that an element was
really being used to describe a second thing (e.g. the author of a Web page)
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Feb 2007Content Packaging for Complex Objects: Technical Workshop 5
DCMI Abstract Model background
• as the various DC syntaxes matured– XHTML, XML and RDF/XML
• the underlying model became more important
• primarily as a mechanism for mapping between syntaxes
• and there have been a number of attempts at applying the RDF model to DC
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Feb 2007Content Packaging for Complex Objects: Technical Workshop 6
DCMI Abstract Model key features
• the DCAM (first published in 2005) attempts to make explicit the model that underpins DC
• the DCAM starts from the central notion of a ‘description set’
– a set of ‘descriptions’ about a group of related things (‘resources’)
– where each ‘description’ is about a single ‘resource’
– and where each ‘description’ is essentially made up of property/value pair ‘statements’
– ‘descriptions sets’ are instantiated as ‘records’ (e.g. using XHTML, XML or RDF/XML) for the purpose of exchanging information between networked systems
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Feb 2007Content Packaging for Complex Objects: Technical Workshop 7
Model summary
record (encoded as HTML, XML or RDF/XML)
description set
description (about a resource (URI))
statement
property (URI) value (URI)
vocabulary encoding scheme (URI)
value string
language(e.g. en-GB)
syntax encodingscheme (URI)
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Feb 2007Content Packaging for Complex Objects: Technical Workshop 8
DCAM and relationships
• the DCAM is very open about the nature of the relationships between the resources described in a description set
– whole / part (e.g. book / chapter / section / page)
– physical / digital (painting / digitised painting)
– object / human (document / author)
– conceptual / physical (work / item)
– or all of the above!
• the relationships between things is articulated in an ‘application model’ and captured using the properties specified in an ‘application profile’
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Feb 2007Content Packaging for Complex Objects: Technical Workshop 9
Example 1 – Book application model
Book0..∞hasPart
Chapter
• here is a very simple ‘application model’…
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Feb 2007Content Packaging for Complex Objects: Technical Workshop 10
Example 1 – pseudo-XML description set
<descriptionSet>
<description resourceURI=http://example.org/mybook>
<statement propertyURI=dcterms:hasPart” valueURI=http://example.org/chapter1 />
<statement propertyURI=dcterms:hasPart” valueURI=http://example.org/chapter2 />
</description>
<description resourceURI=http://example.org/chapter1>
<statement propertyURI=dc:title>
<valueString>Chapter 1</valueString>
</statement>
</description>
<description resourceURI=http://example.org/chapter2>
<statement propertyURI=dc:title>
<valueString>Chapter 2</valueString>
</statement>
</description>
</descriptionSet>
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Feb 2007Content Packaging for Complex Objects: Technical Workshop 11
Note 1 – objects packaged by reference
• note that objects within the package (the resources described within the description set) are passed ‘by reference’
• i.e. their URL is provided
• this is in common with other packaging standards
• passing ‘by value’ (i.e. embedding the object in-line) is theoretically possible using the DCAM ‘rich representation’ mechanism (but this is not discussed further here)
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Feb 2007Content Packaging for Complex Objects: Technical Workshop 12
Note 2 - ordering
• the DCAM has no built-in support for ordering
• the model is graph-based rather than being an ordered tree
• for applications requiring ordering, e.g. the chapters in a book, it would therefore be necessary to invent properties (e.g. my:sequenceNumber) to capture the ordering as part of the description
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Feb 2007Content Packaging for Complex Objects: Technical Workshop 13
Eprints application model
ScholarlyWork
Expression0..∞
isExpressedAs
Manifestation
isManifestedAs
0..∞
Copy
isAvailableAs
0..∞
0..∞
0..∞
isCreatedBy
isPublishedBy
0..∞isEditedBy
0..∞isFundedBy
isSupervisedBy
AffiliatedInstitution
Agent
• here is a more complex ‘application model’…
http://www.ariadne.ac.uk/issue50/allinson-et-al/
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Feb 2007Content Packaging for Complex Objects: Technical Workshop 14
Example 2 – psuedo-XML
<descriptionSet>
<description resourceURI=http://eprints.gla.ac.uk/503/>
<statement propertyURI=dc:title> <valueString>Attempts to detect retrotransposition and de novo deletion of Alus and other dispersed repeats at specific loci in the human genome </valueString> </statement>
<statement propertyURI=eprint:isExpressedAs valueRef=expression1 />
</description>
<description resourceId=expression1 >
<statement propertyURI=eprint:isManifestedAs valueRef=pdfmanifestation />
</description>
<description resourceId=pdfmanifestation >
<statement propertyURI=eprint:isAvailableAs
valueURI=http://eprints.gla.ac.uk/503/01/Eu_J._Hum_Gen.9(2)143_.pdf />
<statement propertyURI=eprint:isAvailableAs
valueURI=http://www.nature.com/ejhg/journal/v9/n2/pdf/5200590a.pdf />
<description>
<!– descriptions of the two copies here -->
</descriptionSet>
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Feb 2007Content Packaging for Complex Objects: Technical Workshop 15
Note 3 - Compound vs. complex objects
• note that the relationships between objects in this example are more complex than hasPart or isPartOf
– because the model doesn’t just deal with digital objects
• it may be worth drawing a distinction between– ‘compound objects’ (where objects have whole / part type structural relationships) and
– ‘complex objects (where there are arbitrary relationships between objects) ??
• most objects in digital libraries are complex… not just compound
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Feb 2007Content Packaging for Complex Objects: Technical Workshop 16
Summary – why DC?
• DC (and the DCAM) provides a simple packaging framework
– where objects within the package are typically passed by reference
– highly flexible and extensible relationship framework between objects
– supports multiple syntax encodings
– compatible with Semantic Web (which allows for possibility of inferencing across complex objects from unknown sources)
• content packaging is largely about relationships – i.e. it is just metadata
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Feb 2007Content Packaging for Complex Objects: Technical Workshop 17
Questions…