WI 4 (CWA1): Guidelines for machine-processable representation of Dublin Core Application Profiles Pete Johnston, UKOLN, University of Bath Thomas Baker,

WI 4 (CWA1): Guidelines for machine-processable representation of Dublin Core Application Profiles

Pete Johnston, UKOLN, University of BathThomas Baker, Fraunhofer-Gesellschaft

CEN/ISSS MMI-DC Meeting

Brussels, 22-23 September 2004

http://www.ukoln.ac.uk/


Machine-processable representation of Dublin Core Application Profiles

• Context• Conceptual model for DCAP• Suggested representation using RDF


Context

• Metadata “application profile”– Recognition that implementers adapt metadata standards to

context– Use terms from multiple metadata vocabularies in combination

• CEN CWA 14855– Guidelines for human-readable representation of DCAP

• Current draft– Make information available in structured form, usable by

applications• Influenced by

– DCMI practice ("Grammatical Principles“, Namespace Policy, declaration of metadata vocabularies, “DCMI Abstract Mode”l)

– W3C Semantic Web activity– Research projects on metadata schema registries


DCMI Abstract Model

• Working Draft of DC Architecture WG• Seeks to make explicit the DC "meta-model"

– what are the component parts of any DC metadata description

– what information these components convey about the resources described by the DC metadata description

– independent of form in which DC metadata description is represented

– closely aligned with RDF meta-model– adopts class hierarchy/property specialisation semantics

of RDFS

DCMI Abstract Model

• Description as set of statements about a subject resource

• Each statement describes a relationship between the subject resource and a second resource (value)

Ref to resource

Ref to property Ref to value

Description

Statement


Fundamentals of DCAP

• DCAP does not define new terms• DCAP references ("uses") terms already defined elsewhere

– Terms may be from multiple independently-created sources• DCAP may describe how use of terms is “constrained”,

adapted, contextualised• N.B. CWA 14855 employed "term usage"; current doc

employs "property usage“– DC differentiates different types of “term”– Only use of properties is “constrained”– Other types of term are referenced

• Only (or at least primarily) as part of constraints on property


Conceptual model for DCAP

• What is a DCAP? • What are the component entities? What

are the related entities?• What are the attributes of a DCAP? And of

these component and related entities?• What types of relationship exist between

these entities?

Property

DCAP

PropertyUsage

usesProperty

usesAsEncodingScheme

Class

hasPropertyUsage

BindingSchema

isExpressedBy

m

n

1

1

m

1 m

1

administersAgency1 m Schema

DocumentisDescribedIn

1

MetadataVocabulary

administers

1

m

1

SchemaDocument

isDescribedIn

1

hasTerm1 m

hasTerm

1

m

m

MetadataVocabulary

subclass

m

n

Class

hasTerm

1

m

subprop

m

n

administersAgency1 m

1

Property

hasTerm

m

Instance

type

n

m

1 SchemaDocument

isDescribedIn

1

1

m

isDescribedIn

Metadata Vocabulary

A set of metadata terms (Properties, Classes, and Instances of those classes) managed as a coherent unit by an Agency

RelationshipsMetadata Vocabulary Is-Administered-By Agency m – 1

MetadataVocabulary Has-Member-Term Property 1 - m

MetadataVocabulary Has-Member-Term Class 1 - m

MetadataVocabulary Has-Member-Term Instance 1 – m

MetadataVocabulary Is-Described-By SchemaDocument 1 - 1

Examples: the DCMES, the DC Terms Vocabulary, the DCMI Type Vocabulary

Property

A Property is a type of relationship between two Resources.

A Property is declared as a term within exactly one Metadata Vocabulary.

A Property may be related to another property by a sub-property relationship: this states that all resources related by the first property are also related by the second property

RelationshipsProperty Is-Member-Term-Of MetadataVocabulary m – 1

Property Is-Subproperty-Of Property m - n

Property Is-Used-By PropertyUsage 1 – m

Examples: dc:creator, dcterms:modified, dcterms:audience(All DCMI elements and element refinements are properties.)

Class

A Class is a group of resources. A Class is declared as a term within exactly one Metadata Vocabulary. A Class may be related to another class by a sub-class relationship: this states that all instances of the first Class are also instances of the second Class.A Resource is related to one or more Classes by a type relationship, and is said to be an Instance of those classes .

RelationshipsClass Is-Member-Term-Of MetadataVocabulary m – 1

Class Is-Subclass-Of Property m – n

Class Has-Instance Instance m - n

Class Is-Used-As-Encoding-Scheme-By PropertyUsage m - n

Examples: dcterms:LCSH, dcterms:W3CDTF, dcmitype:Text, dcmitype:Collection(All DCMI "encoding schemes" and type vocabulary terms are classes.)

DCAP

BindingSchema

isExpressedBy

1

m

Property

usesProperty

1

m

PropertyUsage

hasPropertyUsage

m

1

usesAsEncodingScheme

Class

n

m

administersAgency1 m 1 Schema

DocumentisDescribedIn

1

DC Application Profile (DCAP)

A set of Property Usages, created to meet the functional requirements of an application or context, and managed as a coherent unit by an Agency.

RelationshipsDCAP Is-Administered-By Agency m – 1

DCAP Has-Member PropertyUsage 1 - m

DCAP Is-Described-By SchemaDocument 1 - 1

DCAP Is-Expressed-By BindingSchema 1 - m

Examples: the Simple Dublin Core DCAP, the RDN-DC DCAP, the Renardus DCAP

Attributes of DCAP

URI Reference A URI Reference which identifies the DC application profile

Mandatory Max=1

Title The name or title of the DC application profile

Mandatory Max=1Max=unbounded if allowing for multiple languages

Version An indicator of the version of the DC application profile

Optional Max=1

Status An indicator of the status of the DC application profile

Optional Max=1

Description A summary of the scope and purpose of the DC application profile

Mandatory Max=1Max=unbounded if allowing for multiple languages

Specification A human-readable document that provides more information about the DC application profile

Optional Max=unbounded

Property Usage

A Property Usage is a description of how a previously declared Property from a Metadata Vocabulary is deployed in the context of an application. A Property Usage

– must reference ("use") exactly one Property.– may provide additional documentation on how the property is

interpreted in the context of this application– may provide an application-specific label for the property– may specify obligation for the use of statements referring to the

property (whether it is mandatory, optional, conditional)– may specify constraints on the occurrence of statements

referring to the property– may specify constraints on the permitted values of the property,

by specifying that they are instances of specified classes (i.e. may specify "encoding schemes" for the property)

Property Usage

RelationshipsPropertyUsage Uses Property m – 1

PropertyUsage Uses-As-Encoding-Scheme Class m – n

PropertyUsage Is-Member-Of DCAP m - 1

Examples: the usage of dc:title in the Simple Dublin Core DCAP, the usage of dc:title in RDN-DC DCAP, the usage of dc:title in Renardus DCAP

Attributes of Property Usage

Property Usage URI A URI Reference which identifies the property usage

Mandatory Max=1

Label A human-readable label assigned to the property, in the context of this DC application profile

Optional Max=1Max=unbounded if allowing for multiple languages

Status An indicator of the status of the property usage.

Optional Max=1

Definition A statement of the concept and essential nature of the property, as it is used in this DC Application Profile


Comments Additional information about the property or its use specific to this DC Application Profile


Attributes of Property Usage

Obligation An indication of whether a statement using the property is required to occur in a metadata description conforming to this DC Application Profile

Mandatory Max=1

Condition A description of the condition or conditions according to which a statement using the property in a metadata descripton conforming to this DC Application Profile

Conditional(Mandatory if Obligation = Conditional)

Max=1Max=unbounded if allowing for multiple languages

Occurrences The maximum permitted number of occurrences of statements using the property in a metadata description conforming to this DC Application Profile

Mandatory Max=1


Representation of DCAP : XML?

• Could provide a XML DTD or XML Schema to define an XML format for a DCAP

• But the property usages in a DCAP reference existing terms

• Term descriptions already available, using RDF/RDFS (in some cases, at least!)

• Would require– re-describing terms that are already described (or map

existing data to new format); or– using separate format/model for DCAP (DCAP-XML) and

for metadata vocabulary (RDFS/RDF)


Representation of DCAP: XML Schema?

• An XML Schema describes constraints on the structure of a (class of) XML document(s)

• Abstract Model– Description may be represented as records in multiple

syntaxes– May be multiple XML formats, each with different XML

Schema

• A DCAP specifies the properties/classes used in a description

• So (potentially) one-to-many relation between DCAP and XML Schema


Representation of DCAP: XML Schema?

• However, XML implementers want– to constrain structure of DC-in-XML documents during

creation– to validate structure of DC-in-XML documents post-

creation– … so need XML Schema corresponding to DCAP (for

their chosen XML format)

• DCAP model is (probably?!) rich enough to generate XML Schema…

• …but N.B. that generation process requires additional information about each XML format


Representation of DCAP: RDF?

• RDF provides simple meta-model– Resource-property-value

• Descriptions of terms in DCMI metadata vocabularies already published using RDF– using RDFS and DC vocabularies

• Many other significant vocabularies also available currently or will be available

• By definition DCAP references other terms• Use of RDF facilitates merging of DCAP

description and existing metadata vocabulary descriptions (and resource descriptions)


Representation of DCAP: RDF?

• However, DCAP concept is closely associated with that of document/record/bounded description– mandating that statement with specified property is

present– limiting number of occurrences of statements with

specified property – mandating that value of specified property is instance of

specified class

• Generally, RDF applications tend to adopt "open-world" assumptions– RDFS, OWL designed to support inferencing, rather than

completeness/correctness checks (validation)


RDF representation

• Specify RDF classes and properties corresponding to the entity types, attributes, & relation types in model

• Use existing RDF vocabularies where possible• RDF Vocabulary Description Language (RDF

Schema) provides– a semantics of class hierarchy/property specialisation– an RDF vocabulary to represent RDFS semantics– i.e. properties and classes to describe Properties,

Classes (and Datatypes)• DCMES/DC terms provide

– properties for many descriptive attributes


RDF representation

• RDFS has no concepts of application profile, property usage

• RDFS does not provide– a class to represent a (Metadata) Vocabulary

• So need to provide additional classes and properties where required– The “dcap” vocabulary

• Should provide RDFS descriptions of dcap: terms• N.B. No URIrefs yet assigned for dcap: terms


Example

• RDN-DC– DCAP used for record-sharing between

partners in Resource Discovery Network (RDN)– Sharing over OAI-PMH, so uses XML syntax

• Usage of dc:language– Optional (recommended)– Repeatable– Requires use of RFC3066 encoding scheme

RDN-DC

dc:title

rdn:rdn-dc-dcap

dcap:DCAP

rdf:type

dcap:PropertyUsage

rdf:type

dcap:isMemberOf

dcap:uses

dc:language

rdf:Property

rdf:type

dcterms:RFC3066

rdfs:Class

rdf:typedcap:encodingScheme

<dcap:PropertyUsage>

<dcap:uses rdf:resource="&dcns;language"/>

<dc:description>Use the language codes defined in RFC 3066.</dc:description>

<dcap:obligation rdf:resource="&dcapns;Obligation/recommended"/>

<dcap:maxOccurs>Unbounded</dcap:maxOccurs>

<dcap:encodingScheme rdf:resource="&dctermsns;RFC3066" />

<dcap:isMemberOf rdf:resource="http://www.rdn.ac.uk/ap/rdn_dc"/>

</dcap:PropertyUsage>


Issues

• Choice of URIrefs for dcap: RDF vocabulary terms• Currently, no DCMI-endorsed model for DCAP• Proposed model is largely untested!

– But JISC IEMSR registry in development (similar data model)

• DCMI Abstract Model still work-in-progress– Literal and non-literal values in DC metadata?– Use of literal datatyping for syntax encoding schemes?

• DCAP for description v DCAP for description set • CEN CWA 14855

– more "permissive" view of DCAP?

Documents

WI 4 (CWA1): Guidelines for machine-processable representation of Dublin Core Application Profiles Pete Johnston, UKOLN, University of Bath Thomas Baker,