An Introduction to the DCMI Abstract Model

16

Ap

ril 20

07

Pete Johnston, Eduserv [email protected]

www.eduserv.org.uk/foundation

An Introduction to the DCMI Abstract Model

JISC CETIS Metadata & Digital Repositories SIG meeting, Manchester

16 April 2007JISC CETIS Metadata & Digital Repositories SIG meeting, Manchester

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• Context & Motivation: Why the DCAM?

• The DCMI Abstract Model

• The DCAM & “DC application profiles”

• The DCAM & DCMI “encoding guidelines”

• Dublin Core in 2007


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Context & Motivation: Why the DCAM?


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Why DCAM? Context & Motivation

• Some issues for DCMI c.2003– Metadata vocabularies

• … but what is a DC “element”?

– Encoding guidelines• … but what are we “encoding”?

– DC application profiles• … but what “terms” can we “use”?

– “Simple” and “Qualified” DC

– Grammatical Principles

– DC & the Resource Description Framework


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Why DCAM? Context & Motivation

• Work on DCAM from mid-2003, initiated by Andy Powell• DCMI Recommendation, 2005-03-07• Feedback from

– DCMI Usage Board– DCMI working groups, designers of DCAPs– Implementers of DCAPs– Implementers of metadata registries– Developers/implementers of related specs– Semantic Web community– Researchers

• Revision currently in progress– Proposed Rec for Public Comment, 2007-02-05– Proposed Rec for Public Comment, 2007-04-02


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The DCMI Abstract Model

Proposed Recommendation

http://dublincore.org/documents/2007/04/02/abstract-model/


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• DCAM concerned with description of resources• DCAM adopts Web Architecture/RFC3986 definition of

resource– the term "resource" is used in a general sense for whatever

might be identified by a URI. Familiar examples include an electronic document, an image, a source of information with consistent purpose (e.g., "today's weather report for Los Angeles"), a service (e.g., an HTTP to SMS gateway), a collection of other resources, and so on.

– A resource is not necessarily accessible via the Internet; e.g., human beings, corporations, and bound books in a library can also be resources.

– Likewise, abstract concepts can be resources, such as the operators and operands of a mathematical equation, the types of a relationship (e.g., "parent" or "employee"), or numeric values (e.g., zero, one, and infinity).

– RFC3986 URI Syntax


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• DCAM describes– Components and constructs that make up an

information structure (“DC description set”)– How that information structure is to be interpreted

• DCAM does not describe how to represent DC description set in concrete form

• DCAM describes various types of metadata term, but does not specify the use of any fixed set of terms

• Made up of three related “information models”– Resource model– Description set model– Vocabulary model


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DCAM Resource Model


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DCAM Resource Model

• The “view of the world” on which DC metadata is based

• a described resource is described using one or more property-value pairs

• a property-value pair is made up of – exactly one property and– exactly one value

• a value is a resource• a value is either a literal value or a non-literal value

• i.e. similar to RDF model of binary relations between resources; entity-relational model


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DCAM Description Set Model


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• The structure of DC metadata• Uses URIs to refer to resources & metadata terms (like RDF)

• a description set is made up of one or more descriptions, each of which describes one resource

• a description is made up of – zero or one described resource URI

• identifies described resource

– one or more statements

• a statement is made up of – exactly one property URI

• identifies property

– exactly one value surrogate

• a value surrogate is either a literal value surrogate or a non-literal value surrogate

Description Set

Description

Statement

Property URI

Resource URI

Literal Value Surrogate

Description

Statement

Property URI

Resource URI

Non-Literal Value Surrogate

Statement

Property URI



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• a literal value surrogate is made up of – exactly one value string

• encodes value

• a non-literal value surrogate is made up of– zero or one value URIs

• identifies value

– zero or one vocabulary encoding scheme URI • identifies a set of which the value is a member

– zero or more value strings • represents value

Description Set

Description

Statement

Property URI

Resource URI


Description

Statement

Property URI

Resource URI


Statement

Property URI


Value URI

Vocab Enc Scheme URI

Value URI

Value string

Value string

Value string


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• a value string is either a plain value string or a typed value string

– a plain value string may have an associated value string language

– a typed value string is associated with a syntax encoding scheme URI

• Not going to say more about SES today!

Description Set

Description

Statement

Property URI

Resource URI


Description

Statement

Property URI

Resource URI


Statement

Property URI


Value URI


Value URI

Value string

Value string

Value string

Syntax Enc Scheme URI

Language

Language


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• a value may be described by another description

Description Set

Description

Statement

Property URI

Resource URI


Description

Statement

Property URI

Resource URI


Statement

Property URI


Value URI


Value URI

Value string

Value string

Value string


Language

Language

Description Set

Description

Statement

Property URI


Description

Statement

Property URI

Resource URI


Statement

Property URI



Value URI

Value string

Value string

Value string


Language

Language


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Some example description sets

Description Set

Description

Statement

Property URI

Resource URI

Example 1: Single description containing one statement with non-literal value surrogate


Value URI

Description Set

Description

Statement

<http://purl.org/dc/terms/publisher>

<http://dublincore.org/documents/abstract-model/>

<http://example.org/org/DCMI>

Example 1: Single description containing one statement with non-literal value surrogate

@prefix dcterms <http://purl.org/dc/terms/> .

DescriptionSet ( Description ( ResourceURI ( <http://dublincore.org/documents/abstract-model/> ) Statement ( PropertyURI ( dcterms:publisher ) ValueURI (<http://example.org/org/DCMI> ) ) ))


Property URI Value URI

Description Set

Description

Statement

Property URI

Resource URI

Example 2: Single description containing two statements with non-literal value surrogates

Statement

Property URI




Value URI

Value string

Value string

Value URI

Language

Language

Description Set

Description

Statement


Statement

<http:/purl.org/dc/terms/subject>



<http://example.org/terms/mySH>

“Metadata”

"Métadonnées"

en

fr



<http://example.org/org/DCMI>Property URI Value URI

<http://example.org/org/mySH/h123> Value URIProperty URI


Value String

Value String

@prefix dcterms <http://purl.org/dc/terms/> .

DescriptionSet ( Description ( ResourceURI ( <http://dublincore.org/documents/abstract-model/> ) Statement ( PropertyURI ( dcterms:publisher ) ValueURI (<http://example.org/org/DCMI> ) ) Statement ( PropertyURI ( dcterms:subject ) ValueURI (<http://example.org/mySH/h123> ) VocabEncSchemeURI (<http://example.org/terms/mySH> ) ValueString ( “Metadata” Language (en ) ) ValueString ("Métadonnées" Language (fr ) ) ) ))


Description Set

Description

Statement

Property URI

Resource URI

Example 3: Two descriptions, statements with non-literal value surrogates & literal value surrogates

Statement

Property URI




Value URI

Value string

Value string

Value URI

Language

Language

Description

Resource URI

Statement

Property URI


Value string Language

Description Set

Description

Statement

Statement

<http:/purl.org/dc/terms/subject>



<http://example.org/terms/mySH>

“Metadata”

"Métadonnées"

en

fr



<http://example.org/org/DCMI>Property URI Value URI

<http://example.org/org/mySH/h123> Value URIProperty URI


Value String

Value String

Example 3: Two descriptions, statements with non-literal value surrogates & literal value surrogates

Description

Statement

<http://example.org/org/DCMI>

<http://xmlns.com/foaf/0.1/name>


“Dublin Core Metadata Initiative” en Value StringProperty URI

@prefix dcterms <http://purl.org/dc/terms/> .@prefix foaf <http://xmlns.com/foaf/0.1/> .DescriptionSet ( Description ( ResourceURI ( <http://dublincore.org/documents/abstract-model/> ) Statement ( PropertyURI ( dcterms:publisher ) ValueURI (<http://example.org/org/DCMI> ) ) Statement ( PropertyURI ( dcterms:subject ) ValueURI (<http://example.org/mySH/h123> ) VocabEncSchemeURI (<http://example.org/terms/mySH> ) ValueString ( “Metadata” Language (en ) ) ValueString ("Métadonnées" Language (fr ) ) ) ) Description ( ResourceURI ( <http://example.org/org/DCMI> ) Statement ( PropertyURI ( foaf:name ) LiteralValueString ( “Dublin Core Metadata Initiative” Language (en) ) ) ))


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DCAM Vocabulary Model


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DCAM Vocabulary Model

• a vocabulary is a set of terms (property, class, vocabulary encoding scheme, syntax encoding scheme)

• a resource may be an instance of one or more classes • a resource may be a member of one or more vocabulary

encoding schemes • a property may have a range relationship with one or more

classes• a property may have a domain relationship with one or more

classes• a property may have a subproperty relationship with one or

more properties• a class may have a subclass relationship with one or more

classes

• =~ RDF Schema


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Current/recent issues

• DCAM & RDF– Mapping to RDF graphs specified by Expressing DC

metadata using RDFhttp://dublincore.org/documents/2007/04/02/dc-rdf

• Clarifying distinction between “things” & “strings”• DCAM as abstract syntax for RDF v DCAM as “domain

(metadata) model”– Reflects DCMI community’s view of metadata– Uses concepts developed by that community– Formulated so as to be compatible with RDF/RDFS

• Possibly require further note(s) on merging, inferencing

http://dublincore.org/documents/2007/04/02/dc-rdf


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The DCAM & “DC application profiles”


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The DCAM & “DC application profiles”

• DCAM does not specify the set of terms referenced in a description set

• Notion of “DC application profile” widely used within DCMI and by DC implementers

– Typically annotated lists of terms used in DC metadata so as to meet some domain/community requirements

– Terms defined by DCMI or by other agencies– Currently DCMI has no formal model for DCAP

• DCAP as “description set profile”– Specification of how to construct description sets to

meet some set of requirements• Definition of DCAP based on

– functional requirements– domain model


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The DCAM & “encoding guidelines”


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• DCAM is independent of any concrete syntax

• For transfer between applications, descriptions must be encoded as digital objects (records)

• DCMI “Encoding Guidelines” describe – how description set is serialised/encoded as a

record using a format

– how records conforming to format are decoded/interpreted as description sets

System A

DC DescriptionSet

DC-XMLInstance

Encode

Construct usingDCAM & DCAP

Decode

DC DescriptionSet

Interpret usingDCAM

System B

DC-XMLInstance

<?xml version="1.0"?><dcx:descriptionSet>


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• Current DCMI “Encoding Guidelines” specs– Pre-date development of DCAM

– Use earlier, simpler “DC abstract models”

– Not fully compatible with DCAM description set model

• Currently, no DCMI recommendation for machine-readable format for description set model

• Updating of specs in progress (2007)– DC-XML

– DC in X/HTML link/meta elements

• Meanwhile, some formats defined outside of DCMI– e.g. Eprints DC-XML


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Some thoughts on Dublin Core in 2007


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Dublin Core in 2007

• Not just “a set of 15 elements”

• Not even a set of 15 elements, +70-odd other terms (element refinements, vocabulary encoding schemes, syntax encoding schemes, classes)

• Not just “Simple Dublin Core” and “Qualified Dublin Core”

• Not limited to “simple” “flat” “atomic” descriptions


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Dublin Core in 2007

• a framework (the DCAM)– which describes how to use certain types of terms– ... to make statements...– ... that form descriptions (of resources)– … that can be grouped together as description sets

• a set of specifications for encoding description sets using various formats

• a managed vocabulary of widely useful terms– which can be referenced in statements

• support for defining additional vocabularies of terms• which can be referenced in statements

• support for defining DC application profiles– which describe how to construct description sets for some

particular set of requirements• extensibility, modularity, compatibility with Semantic Web

16

Ap

ril 20

07

Pete Johnston, Eduserv [email protected]

www.eduserv.org.uk/foundation


JISC CETIS Metadata & Digital Repositories SIG meeting, Manchester

Documents

An Introduction to the DCMI Abstract Model