Encoding DC in XHTML, XML and RDF

1
Encoding DC in (X)HTML, XML and RDF
Tutorial at ECDL 2004, Bath September 2004

• Andy Powell
• a.powell_at_ukoln.ac.uk
• UKOLN, University of Bath, UK
• http//www.ukoln.ac.uk/

UKOLN is supported by
2
Contents

• an abstract model for DC (30 mins)
• encoding DC in XHTML (30 mins)
• encoding DC in XML (30 mins)
• encoding DC in RDF/XML (30 mins)
• practical examples
• OAI Protocol forMetadata Harvestingand RSS (20
  mins)
• assigning identifiers (20 mins)

Note you are going to see lots ofangle-brackets
but no XML schemas!
3
Important

• this is a tutorial
• please feel free to ask questionsas we go
  through!

4
Important DCMI documents

• DCMI Abstract Model DRAFThttp//www.ukoln.ac.uk
  /metadata/dcmi/abstract-model/
• Expressing Dublin Core in HTML/XHTML meta and
  link elementshttp//dublincore.org/documents/dcq-
  html/
• Guidelines for implementing Dublin Core in
  XMLhttp//dublincore.org/documents/dc-xml-guideli
  nes/
• Expressing Simple Dublin Core in
  RDF/XMLhttp//dublincore.org/documents/dcmes-xml/
  
• Expressing Qualified Dublin Core in
  RDF/XMLhttp//dublincore.org/documents/dcq-rdf-xm
  l/
• Namespace Policy for the DCMIhttp//dublincore.or
  g/documents/dcmi-namespace/
• DCMI Metadata Termshttp//dublincore.org/document
  s/dcmi-terms/

5
Implementing DC

• this tutorial is about the mechanics of
  implementing DC in HTML, XML and RDF
• it doesnt really consider which implementation
  strategy isthe best!
• ask yourself two questions
• what am I trying to achieve?
• does using HTML, XML or RDF help me achieve it?
• do software and services exist that will support
  the creation and use of mymetadata?

6
Abstract models for DC
7
Why abstract models?

• the first part of this tutorial isnt going to
  show any angle brackets!
• why?
• because before we start creating DCMI
  descriptions we need to understand
• the DCMI view of the world/resources we want to
  describe (the DCMI resource model)
• the DCMI view of the descriptions we make about
  that world (the DCMI description model)

8
DCMI resource model

• each resource that we want to describe has zero
  or more properties
• a property is a specific aspect, characteristic,
  attribute or relation used to describe a resource
• each property has one or more values
• each value is a resource (the physical or
  conceptual entity that is associated with a
  property when it is used to describe a resource)

9
Err but what is a resource?

• W3C/IETF definition of resource is
• anything that has identity. Familiar examples
  include an electronic document, an image, a
  service (e.g., "today's weather report for Los
  Angeles"), and a collection of other resources.
  Not all resources are network "retrievable"
  e.g., human beings, corporations, and bound books
  in a library can also be considered resources.
• i.e. a resource is anything
• physical things (books, cars, people)
• digital things (Web pages, digital images)
• conceptual things (colours,points in time)

10
Yeah, but no, but

• but this seems to be too wide for the things we
  can describe with DC!
• can we really describe people using DC?
• do people have titles and subjects?
• no in general we only use DC to describe a
  sub-set of all resources
• anything covered by the DCMIType list
• Collection, Dataset, Event, Image (Still or
  Moving), Interactive Resource, Service, Software,
  Sound, Text, Physical Object

11
DCMI resource model (2)

• each resource may be a member of one or more
  classes
• each class may be related to one or more other
  classes by a refines (sub-class) relationship
• the two classes share some semantics such that
  all resources that are members of the sub-class
  are also members of the related class

where the resource is the value of a property,
the class is referred to as a vocabulary encoding
scheme
12
DCMI resource model (3)

• each property may be related to exactly one other
  property by a refines (sub-property) relationship
• the two properties share some semantics such that
  all valid values of the sub-property are also
  valid values of the related property

13
DCMI description model

• a description is made up of
• one or more statements (about one, and only one,
  resource) and
• zero or one resource URI (a URI reference that
  identifies the resource being described)
• each statement is made up of
• a property URI (that identifies a property),
• zero or one value URI (that identifies a value of
  the property),
• zero or one encoding scheme URI (that identifies
  the class of the value) and
• zero or more value representations of the value

14
DCMI description model (2)

• each property is an attribute of the resource
  being described
• each property URI may be repeated in multiple
  statements
• the value representation may take the form of a
  value string, a rich value or a related
  description

15
DCMI description model (3)

• each value string is a simple, human-readable
  string that represents the value of the property
• each value string may have an associated encoding
  scheme URI that identifies a syntax encoding
  scheme
• each value string may have an associated value
  string language that is an ISO language tag (e.g.
  en-GB)

16
DCMI description model (4)

• each rich value is some marked-up text, an image,
  a video, some audio, etc. or some combination
  thereof that represents the resource that is the
  value of the property
• each related description is a description of
  (i.e. some metadata about) the resource that is
  the value of the property

17
The 11 principle

• notice that the model indicates that each
  property used in a description must be an
  attribute of the resource being described
• this is commonly referred to as the 11 principle
  - the principle that a DCMI metadata description
  describes one, and only one, resource
• however

18
Description sets

• real-world metadata applications tend to be based
  on loosely grouped sets of descriptions (where
  the described resources are typically related in
  some way)
• known here as description sets
• for example, a description set might comprise
  descriptions of both a painting and the artist

19
DCMI records

• description sets are instantiated, for the
  purposes of exchange between software
  applications, in the form of metadata records
• each record conforms to one of the DCMI encoding
  guidelines (XHTML meta tags, XML, RDF/XML, etc.)

ltdctitlegt a document lt/dctitlegt ltdccreatorgt and
y powell lt/dccreatorgt
20
Values (again!)

• a value is the physical or conceptual entity that
  is associated with a property when it is used to
  describe a resource
• the value of the DC Creator property is a person,
  organisation or service - a physical entitiy
• the value of the DC Date property is a point in
  time - a conceptual entity
• the value of the DC Coverage property may be a
  geographic region or country - a physical entity
• the value of the DC Subject property may be a
  concept - a conceptual entity - or a physical
  object or person - a physical entity
• each of these entities is a resource

21
Simple vs. qualified DC?

• the notions of simple DC and qualified DC are
  often referred to in DCMI discussions
• a view of what these two terms mean is presented
  here
• note that not everyoneagrees with mydefinitions!

22
Simple DC record

• a simple DC record is a record that
• conforms to the abstract model,
• comprises only a single description,
• uses only the 15 properties in the Dublin Core
  Metadata Element Set,
• makes no use of value URIs, encoding schemes,
  rich values or related descriptions.

23
A couple of notes

• there is no guaranteed linkage between a simple
  DC record and the resource being described
  because the resource URI is optional
• such a linkage may be made by encoding the URI of
  the resource as the value string of the DC
  Identifier element, however this is not mandatory
  everything in DC is optional
• while the value string of a property may look
  like a URI, there is nothing in the simple DC
  model that indicates this is the case

at their own risk, implementations may choose to
guess which value strings are URIs and which are
not
24
Qualified DC model

• a qualified DC record is a record that
• conforms to the DCMI abstract model,
• contains at least one property taken from the
  DCMI Metadata Terms recommendation

25
A couple of notes

• it is still the case that there is no guaranteed
  linkage between a qualified DC record and the
  resource being described!
• a linkage may be made by encoding the URI of the
  resource as the value string of the DC Identifier
  element, however this is not mandatory
  everything in DC is optional

where the value of a property is a URI, we can
now indicate that it is a URI by using the URI
encoding scheme
26
Dumb-down

• the process of translating a qualified DC
  metadata record into a simple DC metadata record
  is normally referred to as dumbing-down
• can be separated into two parts property
  dumb-down and value dumb-down.
• each of these processes can be be approached in
  one of two ways
• informed dumb-down
• uninformed dumb-down

27
Dumb and dumberer

• informed dumb-down takes place where the software
  performing the dumb-down algorithm has knowledge
  built into it about the property relationships
  and values being used within a specific DCMI
  metadata application
• uninformed dumb-down takes place where the
  software performing the dumb-down algorithm has
  no prior knowledge about the properties and
  values being used

28
Dumb-down algorithm
element
value
uninformed
informed

• and in all cases
• ignore any related descriptions and rich values,
• ignore any encoding scheme URIs.

29
Encoding DC in XHTML (and HTML!)
30
What is being described?

• a DC record embedded in an (X)HTML document
  describes that document
• if you want to describe something else, dont
  embed it in the (X)HTML document!
• not everyone would
  agree with this

31
Simple DC elements

• use the name and content attributes of the
  XHTML ltmetagt element to encode the DC element
  (one of the 15 DCMES elements) and it's value
  string. Use the following patternltmeta
  name"DC.element" content"Value string" /gt
• for exampleltmeta name"DC.date"
  content"2001-07-18" /gt
• the element names of the 15 DCMES
  elementsalways have a lower-case first letter

32
Simple DC values

• value strings go in the XHTML ltmetagt element
  content attribute
• the string in the content attribute is defined
  to be CDATA, i.e. a sequence of characters from
  the document character set which may include
  character entities
• long value strings may be wrappedacross
  multiple lines as necessarywill need to
  escape some characters, amp, lt, gt, etc

33
Language of the value

• where the language of the value string is
  indicated, it should be encoded using the
  xmllang attribute of the XHTML ltmetagt element.
  For exampleltmeta name"DC.subject"
  xmllang"en" content"seafood" /gtltmeta
  name"DC.subject" xmllang"fr" content"fruits
  de mer" /gt

34
Repeated elements

• multiple property values should be encoded by
  repeating the XHTML ltmetagt element for that
  property, for exampleltmeta name"DC.title"
  content"First title" /gtltmeta name"DC.title"
  content"Second title" /gt

35
Other DC elements

• use the name and content attributes of the
  XHTML ltmetagt element to encode the DC element
  (e.g. audience) and it's value. Use the following
  patternsltmeta name"DCTERMS.element"
  content"Value" /gt
• for exampleltmeta name"DCTERMS.audience"
  content"software developers" /gt
• element names may be mixed-case butshould
  always have a lower-case first letter

36
Element refinements

• use the name and content attributes of the
  XHTML ltmetagt element to encode the element
  refinement and it's value. Use the following
  patternltmeta name"DCTERMS.elementRefinement
  content"Value" /gt
• for exampleltmeta name"DCTERMS.modified"
  content"2001-07-18" /gt

37
Element refinements (2)

• element refinements should use the names
  specified inDCMI Metadata Termshttp//dublinco
  re.org/documents/dcmi-terms/
• as a general rule, element refinement names may
  be mixed-case but should always have a lower-case
  first letter

38
Encoding schemes

• encoding schemes are encoded using the scheme
  attribute of the XHTML ltmetagt element, using the
  following patternltmeta name"DC.element"
  scheme"DCTERMS.Scheme" content"Value" /gt
• for exampleltmeta name"DC.date"
  scheme"DCTERMS.W3CDTF" content"2001-07-18"
  /gt

39
Encoding schemes (2)

• encoding schemes should use the names specified
  inDCMI Metadata Termshttp//dublincore.org/doc
  uments/dcmi-terms/
• as a general rule, encoding scheme names may be
  mixed-case but should always start with an
  upper-case letter. Encoding scheme names are
  often all upper-case

40
Handling namespaces

• the DC. and DCTERMS. prefixes are used to
  indicate the namespace from which the property is
  taken
• put the namespace URI in an XHTML ltlinkgt
  elementltlink rel"schema.DC"
  href"http//purl.org/dc/elements/1.1/" /gtltlink
  rel"schema.DCTERMS" href"http//purl.org/dc/term
  s/" /gt
• while any string is allowable as the prefix,
  current practice is to use DC. and DCTERMS.

41
Value URIs

• where the value of a property is the URI of
  another resource (e.g. DC.relation) an
  alternative form of encoding using the XHTML
  ltlinkgt element is preferred. Use the following
  patternltlink rel"propertyName"
  hrefvalueURI" /gt
• for exampleltlink rel"DC.relation"href"http/
  /www.example.org/" /gtltlink rel"DCTERMS.reference
  s"href"http//www.example.org/176459.pdf" /gt

42
HTML profile

• to give recipient software applications an
  indication of the XHTML profile that was used to
  encode the DCMI metadata, the profile attribute
  of the XHTML ltheadgt element should be
  usedlthead profile"http//dublincore.org/docum
  ents/dcq-html/"gt

43
The case of names

• note that some of the old DCMI documents
  recommend(ed) using an uppercase first letter for
  the names of DCMES elements and element
  refinements, e.g. using Title rather than
  title
• this form of DCMES element naming is acceptable
  but is no longer considered the preferred form

44
The case of names (2)

• in general, any software applications that
  consume DC records embedded into XHTML Web pages
  should ignore the case of names and should treat
  both . (full-stop) and (colon) as valid
  characters after the prefix
• i.e. all the following forms should be treated as
  being equivalent ltmeta name"DC.date"
  content"2001-07-18" /gt ltmeta name"DC.Date"
  content"2001-07-18" /gt ltmeta name"dc.date"
  content"2001-07-18" /gt ltmeta name"dcdate"
  content"2001-07-18" /gt

45
Older versions of HTML

• all the examples in this tutorial conform to
  XHTML 1.0
• most of the recommendations in this tutorial can
  be applied to older versions of HTML (e.g. HTML
  4.01) but
• use lang rather than xmllang
• older versions of HTML do not require the
  trailing / before the closing gt in the HTML
  ltmetagt element
• very old versions of HTML have no ltmetagt scheme
  attribute

46
Mixing DC and non-DC

• DC metadata can be mixed with non-DC metadata in
  XHTML ltmetagt elements
• the following example embeds DC, AGLS and
  unspecified metadata properties in the same XHTML
  Web pageltlink rel"schema.DC"
  href"http//purl.org/dc/elements/1.1/" /gtltlink
  rel"schema.AGLS"href"http//www.naa.gov.au/reco
  rdkeeping/gov_online/agls/1.2" /gtltmeta
  name"DC.title" content"Services to Government"
  /gtltmeta name"keywords" content"archives,
  information management, public administration"
  /gtltmeta name"AGLS.Function" scheme"AGIFT"
  content"recordkeeping standards" /gt

47
A couple of examples

• Simple DCexample 1
• Qualified DCexample 2
• ScreenCam of using DC-dothttp//www.ukoln.ac.uk/
  metadata/dcdot/

48
Encoding DC in XML
49
Introduction to XML

• this section is based onGuidelines for
  implementing Dublin Core in XMLhttp//dublincore.
  org/documents/dc-xml-guidelines/
• nine recommendations for encoding DC in XML
• Note these recommendations do not create
  RDF/XML. This is not intended to imply that
  plain XML is better than RDF/XML RDF is covered
  in the next section!

50
Recommendation 1

• implementers should base their XML applications
  on XML Schemas rather than XML DTDs
• approaches based on XML Schemas are more flexible
  and are more easily re-used within other XML
  applications
• in some cases it may be sensible to provide
  both an XML Schema and a DTD for the application.
  Where XML Schemas are not used, a DTD should be
  provided instead

51
Recommendation 1 (2)

• the DCMI maintains a list of XML schemas that are
  in use in projects or products using DCMI
  metadataDCMI Metadata expressed in XML Schema
  Languagehttp//dublincore.org/schemas/xmls/

52
Recommendation 2

• implementers should use URI references (see
  later) to uniquely identify DC elements, element
  refinements and encoding schemesDC namespaces
  are defined in the DCMI Namespace
  Recommendation...

53
Container elements

• note that it is anticipated that records will be
  encoded within one or more container XML
  element(s) of some kind
• this tutorial makes no recommendations for the
  name of any container element, nor for the
  namespace that the element should be taken from
• candidate container element names include ltdcgt,
  ltdublinCoregt, ltresourcegt, ltrecordgt and ltmetadatagt

54
Recommendation 3

• implementers should encode properties as XML
  elements and values as the content of those
  elements
• the name of the XML element should be an XML
  qualified name (QName) of the propertyltdctitlegt
  Dublin Core in XMLlt/dctitlegt
• do not use constructs likeltdctitle
  value"Dublin Core in XML" /gt

55
Recommendation 4

• the property names for the 15 DC elements should
  be all lower-caseltdctitlegtDublin Core in
  XMLlt/dctitlegt
• do not useltdcTitlegtDublin Core in
  XMLlt/dcTitlegt

56
Recommendation 5

• multiple property values should be encoded by
  repeating the XML element for that
  propertyltdctitlegtFirst titlelt/dctitlegt
  ltdctitlegtSecond titlelt/dctitlegt

57
Simple DC example

• example 3

58
Recommendation 6

• element refinements should be treated in the same
  way as other properties
• the name of the XML element should be an XML
  qualified name (QName)ltdctermsavailablegt2002-0
  6lt/dctermsavailablegt
• do not use any of the followingltdcdate
  refinement"available"gt2002-06lt/dcdategtltdcdate
  type"available"gt2002-06lt/dcdategtltdcdategt
  ltdctermsavailablegt2002-06 lt/dctermsavailablegt
  lt/dcdategt

59
Recommendation 6 (2)

• element refinements are properties in their own
  right and are therefore best encoded in a similar
  way to other DC elements
• in particular, it should be noted that element
  refinements may have further refinements of their
  own (e.g. format is refined by extent which
  might be further refined by duration)
• nesting does not mean refinement
• nesting might be used for other purposes

60
Recommendation 7

• encoding schemes should be implemented using the
  'xsitype' attribute of the XML element for the
  property
• the name of the encoding scheme should be given
  as the attribute value, and should be in the form
  of an XML qualified name (QName)ltdcidentifier
  xsitype"dctermsURI"gt http//www.ukoln.ac.uk/
  lt/dcidentifiergt

61
Recommendation 7 (2)

• it should be noted that there may be existing DC
  XML applications that use other conventions to
  support encoding schemes, notably the use of a
  scheme attribute of the XML element for the
  property
• therefore, it may be sensible for software
  applications that consume DC XML to be fairly
  liberal in what they accept

62
Recommendation 8

• elements, element refinements and encoding
  schemes should use the names specified inDCMI
  Metadata Termshttp//dublincore.org/documents/dcm
  i-terms/
• note, the 15 DCMES element names all start with
  a lowercase letter

63
Recommendation 8 (2)

• element and element refinement names may be
  mixed-case but should always have a lower-case
  first letter
• encoding scheme names may be mixed-case but
  should always start with an upper-case
  letterltdctermsisPartOf xsitype"dctermsURI"gt
  http//www.bbc.co.uk/lt/dctermsisPartOfgt
  ltdctermstemporal xsitype"dctermsPeriod"gtname
  The Great Depression start1929 end1939
  lt/dctermstemporalgt

64
Recommendation 9

• where the language of the value is indicated, it
  should be encoded using the xmllang
  attributeltdcsubject xmllang"en"gt
  seafoodlt/dcsubjectgtltdcsubject xmllang"fr"gt
  fruits de merlt/dcsubjectgt

65
Some examples

• Qualified DCexample 4
• DC and IMSexample 5
• DC, IMS and ODRLexample 6

HEALTH WARNING Examples 5 and 6 may seriously
damage your interoperability!
66
Encoding DC in RDF
67
What is RDF?

• Resource Description Framework
• W3C recommendation for metadata
• model and syntax(es)
• XML is most common syntax in use on the Web
• underpins the semantic WebW3C - Resource
  Description Framework (RDF)http//www.w3.org/RDF/

68
Why use RDF?

• RDF provides shared metadata model
• shared meaning
• metadata can be shared between applications that
  have little or no knowledge about each other
• e.g. an RDF-based bibliographic application can
  consume RDF-based geospatial metadata and have
  'some' knowledge of what it meanswith (X)HTML
  and XML encodings, softwareapplications must
  have understanding hard-codedinto them

69
DC in RDF

• DC abstract models map easily onto the RDF model
  (because RDF was the basis for them!)
• DC in RDF/XML syntax is an encoding of the RDF
  model in XML
• simple DC is similar to the non-RDF XML we've
  seen already
• but with the addition of ltrdfRDFgt and
  ltrdfDescriptiongt container elements
• example 7

70
RDF basics the model

• model based on triples
• a resource has a property which has a value
• often represented as an arc-node diagram (or
  graph)
• resources and properties are identified using URI
  references

property
resource
value
71
A more concrete example

• The graph below approximately translates into
  English as
• the resource identified by the URI
  http//example.org/ has a dccreator that is
  represented by the string Andy Powell

http//purl.org/dc/elements/1.1/creator
http//example.org/
Andy Powell
72
Values as resources

• values can be resources too
• means that we can then attach properties to the
  value as well as to the original resource
• build up quite complex graphs

http//example.org/
dccreator
myname
myphoneNumber
Andy Powell
01225 383933
73
Typed and blank nodes

• nodes can be blank (to represent resources that
  have not be assigned a URI)
• can also indicate the class of a resource using
  the rdftype property

myPerson
rdftype
http//example.org/
dccreator
myname
myphoneNumber
Andy Powell
01225 383933
74
Qualified DC in RDF

• now ready to look at some more complex examples
• for full details about how to encode DC in RDF
  seeExpressing Simple Dublin Core in
  RDF/XMLhttp//dublincore.org/documents/dcmes-xml/
  Expressing Qualified Dublin Core in
  RDF/XMLhttp//dublincore.org/documents/dcq-rdf-xm
  l/

75
Case study 1 dccreator
lt?xml version"1.0"?gt ltrdfRDF xmlnsrdfhttp//ww
w. xmlnsrdfshttp//www.w3.org/ xmlnsdchttp/
/purl.org/dc/ xmlnsmy"http//purl.org"gt
ltrdfDescriptiongt ltdccreatorgt
ltrdfDescriptiongt ltrdfvaluegt
Andy Powell lt/rdfvaluegt
ltmyemailgt a.powell_at_ukoln.ac.uk
lt/myemailgt lt/rdfDescriptiongt
lt/dccreatorgt lt/rdfDescriptiongt lt/rdfRDFgt
Example RDF description using dccreator
76
Case study 1 dccreator
Andy Powell
rdfslabel
dccreator
Andy Po
myname
myemail
a.powell_at_uko
a.powell_at_uko
myaffiliation
UKOLN, Univ
and the RDF model it represents.
77
Case study 1 dccreator
relatedMetadata
Andy Powell
rdfslabel
dccreator
Andy Po
myname
myemail
a.powell_at_uko
a.powell_at_uko
myaffiliation
UKOLN, Univ
But we dont want to embed all this information
into every instance metadata record do we?
78
Case study 1 dccreator
Andy Powell
rdfslabel
dccreator
Andy Po
myname
myemail
a.powell_at_uko
a.powell_at_uko
myaffiliation
UKOLN, Univ
Need to separate part of the information out and
store it in a single place in this case in a
directory service
79
Case study 1 dccreator
Andy Powell
rdfslabel
dccreator
Andy Po
valueURI
valueURI
myname
myemail
a.powell_at_uko
a.powell_at_uko
myaffiliation
UKOLN, Univ
To do this we need to assign a URI (the
valueURI) to the anonymous value node
80
Case study 1 dccreator
relatedMetadataURI
Andy Powell
rdfslabel
dccreator
Andy Po
valueURI
valueURI
myname
myemail
a.powell_at_uko
a.powell_at_uko
myaffiliation
UKOLN, Univ
The document containing this information is
itself an RDF resource (the relatedMetadata)
and has a URI
81
Case study 1 dccreator
relatedMetadataURI
Andy Powell
rdfslabel
dccreator
Andy Po
valueURI
valueURI
myname
myemail
rdfsseeAlso
a.powell_at_uko
a.powell_at_uko
myaffiliation
UKOLN, Univ
Use rdfseeAlso to form linkage between
description and relatedMetadata
82
Case study 2 dcsubject
lt?xml version"1.0"?gt ltrdfRDF xmlnsrdfhttp//ww
w. xmlnsrdfshttp//www.w3.org/ xmlnsdchttp/
/purl.org/dc/ xmlnsdcterms"http//purl.org"gt
ltrdfDescriptiongt ltdcsubjectgt
ltdctermsMESHgt ltrdfvaluegt
D08.586.682.075.400 lt/rdfvaluegt
ltrdfslabelgt Formate Dehydrogenase
lt/rdfslabelgt lt/dctermsMESHgt
lt/dcsubjectgt lt/rdfDescriptiongt lt/rdfRDFgt
Example RDF description using dcsubject (taken
from Qualified DC in RDF recommendation
83
Case study 2 dcsubject
lt?xml version"1.0"?gt ltrdfRDF xmlnsrdfhttp//ww
w. xmlnsrdfshttp//www.w3.org/ xmlnsdchttp/
/purl.org/dc/ xmlnsdcterms"http//purl.org"gt
ltrdfDescriptiongt ltdcsubjectgt
ltdctermsMESHgt ltrdfvaluegt
D08.586.682.075.400 lt/rdfvaluegt
ltrdfslabelgt Formate Dehydrogenase
lt/rdfslabelgt lt/dctermsMESHgt
lt/dcsubjectgt lt/rdfDescriptiongt lt/rdfRDFgt
Formated
rdfslabel
dcsubject
rdfsvalue
D08.586
rdftype
rdftype
dctermsMESH
and the RDF model it represents.
84
Case study 2 dcsubject
lt?xml version"1.0"?gt ltrdfRDF xmlnsrdfhttp//ww
w. xmlnsrdfshttp//www.w3.org/ xmlnsdchttp/
/purl.org/dc/ xmlnsdcterms"http//purl.org"gt
ltrdfDescriptiongt ltdcsubjectgt
ltdctermsMESHgt ltrdfvaluegt
D08.586.682.075.400 lt/rdfvaluegt
ltrdfslabelgt Formate Dehydrogenase
lt/rdfslabelgt lt/dctermsMESHgt
lt/dcsubjectgt lt/rdfDescriptiongt lt/rdfRDFgt
relatedMetadata
Formated
rdfslabel
dcsubject
rdfsvalue
D08.586
rdftype
rdftype
dctermsMESH
But we dont want to embed all this information
into every instance metadata record do we?
85
Case study 2 dcsubject
lt?xml version"1.0"?gt ltrdfRDF xmlnsrdfhttp//ww
w. xmlnsrdfshttp//www.w3.org/ xmlnsdchttp/
/purl.org/dc/ xmlnsdcterms"http//purl.org"gt
ltdctermsMESHgt ltrdfvaluegt
D08.586.682.075.400 lt/rdfvaluegt
ltrdfslabelgt Formate Dehydrogenase
lt/rdfslabelgt lt/dctermsMESHgt lt/rdfRDFgt
lt?xml version"1.0"?gt ltrdfRDF xmlnsrdfhttp//ww
w. xmlnsrdfshttp//www.w3.org/ xmlnsdchttp/
/purl.org/dc/ xmlnsdcterms"http//purl.org"gt
ltrdfDescriptiongt ltdcsubjectgt
ltdctermsMESHgt ltrdfvaluegt
D08.586.682.075.400 lt/rdfvaluegt
lt/dctermsMESHgt lt/dcsubjectgt
lt/rdfDescriptiongt lt/rdfRDFgt
D08.586
Formated
rdfslabel
dcsubject
Formated
rdftype
rdftype
dctermsMESH
dctermsMESH
Need to separate part of the information out and
store it in a single place in this case with
the terminology owner
86
Case study 2 dcsubject
lt?xml version"1.0"?gt ltrdfRDF xmlnsrdfhttp//ww
w. xmlnsrdfshttp//www.w3.org/ xmlnsdchttp/
/purl.org/dc/ xmlnsdcterms"http//purl.org"gt
ltdctermsMESHgt ltrdfvaluegt
D08.586.682.075.400 lt/rdfvaluegt
ltrdfslabelgt Formate Dehydrogenase
lt/rdfslabelgt lt/dctermsMESHgt lt/rdfRDFgt
lt?xml version"1.0"?gt ltrdfRDF xmlnsrdfhttp//ww
w. xmlnsrdfshttp//www.w3.org/ xmlnsdchttp/
/purl.org/dc/ xmlnsdcterms"http//purl.org"gt
ltrdfDescriptiongt ltdcsubjectgt
ltdctermsMESHgt ltrdfvaluegt
D08.586.682.075.400 lt/rdfvaluegt
lt/dctermsMESHgt lt/dcsubjectgt
lt/rdfDescriptiongt lt/rdfRDFgt
D08.586
Formated
rdfslabel
dcsubject
valueURI
valueURI
Formated
rdftype
rdftype
dctermsMESH
dctermsMESH
To do this we need to assign a URI (the
valueURI) to the anonymous value node
87
Case study 2 dcsubject
lt?xml version"1.0"?gt ltrdfRDF xmlnsrdfhttp//ww
w. xmlnsrdfshttp//www.w3.org/ xmlnsdchttp/
/purl.org/dc/ xmlnsdcterms"http//purl.org"gt
ltdctermsMESHgt ltrdfvaluegt
D08.586.682.075.400 lt/rdfvaluegt
ltrdfslabelgt Formate Dehydrogenase
lt/rdfslabelgt lt/dctermsMESHgt lt/rdfRDFgt
lt?xml version"1.0"?gt ltrdfRDF xmlnsrdfhttp//ww
w. xmlnsrdfshttp//www.w3.org/ xmlnsdchttp/
/purl.org/dc/ xmlnsdcterms"http//purl.org"gt
ltrdfDescriptiongt ltdcsubjectgt
ltdctermsMESHgt ltrdfvaluegt
D08.586.682.075.400 lt/rdfvaluegt
lt/dctermsMESHgt lt/dcsubjectgt
lt/rdfDescriptiongt lt/rdfRDFgt
relatedMetadataURI
D08.586
Formated
rdfslabel
dcsubject
valueURI
valueURI
Formated
rdftype
rdftype
dctermsMESH
dctermsMESH
The document containing this information is
itself an RDF resource (the relatedMetadata)
and has a URI
88
Case study 2 dcsubject
lt?xml version"1.0"?gt ltrdfRDF xmlnsrdfhttp//ww
w. xmlnsrdfshttp//www.w3.org/ xmlnsdchttp/
/purl.org/dc/ xmlnsdcterms"http//purl.org"gt
ltdctermsMESHgt ltrdfvaluegt
D08.586.682.075.400 lt/rdfvaluegt
ltrdfslabelgt Formate Dehydrogenase
lt/rdfslabelgt lt/dctermsMESHgt lt/rdfRDFgt
lt?xml version"1.0"?gt ltrdfRDF xmlnsrdfhttp//ww
w. xmlnsrdfshttp//www.w3.org/ xmlnsdchttp/
/purl.org/dc/ xmlnsdcterms"http//purl.org"gt
ltrdfDescriptiongt ltdcsubjectgt
ltdctermsMESHgt ltrdfvaluegt
D08.586.682.075.400 lt/rdfvaluegt
lt/dctermsMESHgt lt/dcsubjectgt
lt/rdfDescriptiongt lt/rdfRDFgt
relatedMetadataURI
D08.586
Formated
rdfslabel
dcsubject
valueURI
valueURI
rdfsseeAlso
Formated
rdftype
rdftype
dctermsMESH
dctermsMESH
Use rdfseeAlso to form linkage between
description and relatedMetadata
89
Abstract DC model
lt?xml version"1.0"?gt ltrdfRDF xmlnsrdfhttp//ww
w. xmlnsrdfshttp//www.w3.org/ xmlnsdchttp/
/purl.org/dc/ xmlnsdcterms"http//purl.org"gt
ltdctermsMESHgt ltrdfvaluegt
D08.586.682.075.400 lt/rdfvaluegt
ltrdfslabelgt Formate Dehydrogenase
lt/rdfslabelgt lt/dctermsMESHgt lt/rdfRDFgt
lt?xml version"1.0"?gt ltrdfRDF xmlnsrdfhttp//ww
w. xmlnsrdfshttp//www.w3.org/ xmlnsdchttp/
/purl.org/dc/ xmlnsdcterms"http//purl.org"gt
ltrdfDescriptiongt ltdcsubjectgt
ltdctermsMESHgt ltrdfvaluegt
D08.586.682.075.400 lt/rdfvaluegt
lt/dctermsMESHgt lt/dcsubjectgt
lt/rdfDescriptiongt lt/rdfRDFgt
relatedMetadataURI
resource
resource
related description
D08.586
Formated
valueString
value string (language)
rdfslabel
dcsubject
valueURI
property
property
valueURI
valueURI
value URI
rdfsseeAlso
Formated
rdftype
rdftype
dctermsMESH
dctermsMESH
In terms of abstract DC model we now have
resource, property, value URI, value string (and
value string language), encoding scheme, related
description
encoding scheme
90
Practical examples OAI and RSS
91
OAI-PMH

• OAI Protocol for Metadata Harvesting
• simple protocol for sharing metadata records
  between applications
• currently at version 2.0
• based on HTTP, XML, XML Schema and XML namespaces
• allows a harvester to ask a remote repository for
  some or all of its metadata records

92
OAI-PMH (2)

• simple DC is default (mandatory) record format
• supports any record format provided it can be
  encoded using XML (e.g. DC, IMS, MARC, ODRL,
  )Open Archives Initiativehttp//www.openarchiv
  es.org/

93
OAI-PMH example

• record from the American Memory repository at the
  Library of Congresshttp//memory.loc.gov/cgi-bin
  /oai2_0
• example 8
• ScreenCam of using the repository explorer
• GetRecord for record identifieroailcoa1.loc.gov
  loc.gmd/g3701p.rr003570

94
RSS

• RDF Site Summary or Rich Site Summary (or even
  Really Simple Syndication)
• at least 3 different versions (0.91, 1.0 and 2.0)
• all based on XML but not compatible
• simple format for sharing news feeds on the Web
• RSS channels list of items
• channels updated by updating XML file
• RSS clients gather XML on regular basis

95
RSS 1.0 and DC example

• RSS 1.0 based on RDF
• most flexible and extensible of the RSS family
  - not necessarily the most widely deployed
• can include DC in both channel and item
  descriptions
• example 9
• full documentation atRDF Site Summary 1.0
  Modules Qualified Dublin Corehttp//web.resource
  .org/rss/1.0/modules/dcterms/

96
Assigning identifiers tometadata terms
97
Whats the problem?

• the terms used in DCMI metadata records must be
  assigned a URI reference before they can be used
• qualified DC application profiles generally use
  local additions to DCMI terms
• therefore these additional terms must be assigned
  a URI reference
• a URI reference is a URI with an optional
  fragment identifier

98
DCMI terms URI references

• all DCMI terms have already been assigned URI
  references
• for examplehttp//purl.org/dc/elements/1.1/titl
  ehttp//purl.org/dc/terms/dateCopyrighted

99
Namespace-name issues

• encoding syntaxes split the term URI reference
  into two parts
• namespace
• name
• the namespace is shortened to a namespace prefix
• for example
• DC.title (XHTML)
• dctitle (XML, RDF/XML)

100
Guidelines

• for groups of related terms, URI references are
  typically assigned such that they can share a
  namespace prefix
• all term URI references should resolve to a human
  and/or machine readable description of the term
• term URI references should use a registered URI
  scheme
• term URI references should be assigned with the
  intention of them being as persistent as the
  Internet

101
A note on namespaces

• DCMI namespaceA DCMI namespace is a collection
  of DCMI terms (a collection of names)
• DCMI termA DCMI term is a DCMI element, a DCMI
  qualifier or term from a DCMI-maintained
  controlled vocabulary
• each DCMI namespace is identified by a URI each
  name in the namespace is also a URI
• a mechanism for making DCMI terms unique

102
How do I assign URIs?

• no clear recommended best practice in this area
  yet!
• four strategies for assigning URIs are presented
  here
• there are other strategies!

103
Using project/service URIs

• simple to do
• but danger of lack of persistence
• exampleshttp//myservice.org/terms/priceltmyser
  vicepricegt (XML, RDF/XML)MYSERVICE.price
  (XHTML)http//myproject.org/metadata/vocabs/colo
  rRedltmyprojectRedgt (RDF/XML)

104
Using PURLs

• PURLs are persistent URLs (under the purl.org
  domain)
• used by DCMI, RSS and others to provide
  persistent term URI references
• exampleshttp//purl.org/dc/elements/1.1/titlelt
  dctitlegt (XML, RDF/XML)DC.title
  (XHTML)http//purl.org/rss/1.0/linkltrsslinkgt
  (XML, RDF/XML)

105
Using xmlns.com

• domain registered explicitly for use for XML
  namespaces
• but persistence policy a little unclear
• used for FOAF terms
• examplehttp//xmlns.cm/foaf/0.1/firstNameltfoaf
  firstNamegt (RDF/XML)

106
Using info URIs

• info URIs specifically designed for identifying
  vocabulary terms
• but not a registered scheme yet and there is
  currently some discussion (i.e. argument!) on
  various lists about whether they are a good idea
• exampleinfoddc/22/eng//004.678

107
What have we learned?

• an abstract model for DC
• encoding DC in XHTML
• encoding DC in XML
• encoding DC in RDF/XML
• two practical examples
• OAI Protocol forMetadata Harvesting
• RSS
• how to assign identifiersto new metadata terms

108
Questions?