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DC-ARCHITECTURE  February 2012

DC-ARCHITECTURE February 2012

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Subject:

DCAM: Alistair on "Son of DC" (2007)

From:

Thomas Baker <[log in to unmask]>

Reply-To:

DCMI Architecture Forum <[log in to unmask]>

Date:

Tue, 21 Feb 2012 21:00:33 -0500

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (146 lines)

Some more excerpts...

----------------------------------------------------------------------
http://aliman.googlecode.com/svn/trunk/sodc/SoDC-0.2/index.html
    
    Abstract:
        Son of Dublin Core (SoDC) consists of two main components.
        The first component, SoDC-XML, is a concrete XML syntax for encoding
        graph-based (meta)data -- data that describes things which are related
        to other things. SoDC-XML is designed to allow graph-based (meta)data
        to be embedded in harvesting protocols such as OAI-PMH, and to make
        automatic quality control via simple syntactic validation really easy.
        The second component, SoDC-CL, is a language for expressing
        application-specific syntax constraints over a (meta)data graph, to
        enable automatic validation of (meta)data against an "application
        profile".
        SoDC also includes two supporting utilities. SchemaGen is a tool for
        automatically generating validation schemas from SoDC-CL documents.
        TurtleGen is a tool for translating SoDC-XML documents into the Turtle
        RDF syntax. 

    1. Introduction
        1.1. Virtual Metadata
            The notion of a graph - a set of nodes connected to other nodes -
            provides a powerful abstraction for metadata interoperability. All
            metadata can be viewed, or "virtualised", through this abstraction.
            Virtualisation leads directly to substantial cost savings, because
            metadata software systems can be "syntax-independent" -- written
            once then deployed for multiple concrete syntaxes. An analogy is
            the Java programming language, which provides a virtualisation of
            the underlying operating systems, allowing software to be
            "platform-independent" -- written once then deployed across
            multiple platforms.

        1.2. Joined-up Metadata
            In addition to cost savings through virtualisation, metadata graphs
            provide additional benefits. Graphs can be easily merged with other
            graphs, providing a mechanism for integrating or "joining up"
            metadata from disparate sources. The utility of this feature is
            highly significant, as various metadata silos seek to provide an
            experience whereby users can browse seamlessly across the
            relationships between scholarly works, scientific datasets,
            projects, organisations, people and subject areas. This
            "Webification" of metadata describing all aspects the scholarly
            lifecycle can only be achieved by joining up metadata from multiple
            silos, where each silo only holds a part of the "overall picture".

       1.3. Meaningful Metadata
            A further benefit is that semantics can be precisely defined for
            graph-based metadata. Semantics have immediate, short term utility,
            because they provide (amongst other things) a means for graceful
            degradation of interoperability between applications. This
            principle is already crudely illustrated by the "dumb-down"
            procedure defined by the Dublin Core Metadata Initiative for its
            metadata architecture. Dumb-down means that not all applications
            have to understand the details of all metadata schemas -- specific
            schemas can be designed for specific applications, without
            compromising interoperability at more general levels.

            The thin layering of application-specific semantics on metadata
            graphs provides a graceful, less crude, replacement to "dumb-down".
            This approach allows enormous flexibility and removes social
            barriers otherwise created by the need for wide acceptance of large
            and detailed metadata specifications, allowing applications to be
            designed quickly and efficiently to satisfy the requirements of a
            specific community, without fear of isolating that community from
            its neighbours.

        1.4. Aligning Communities

            Metadata virtualisation, via the notion of metadata graphs, is
            already gaining traction in a number of important communities. The
            Resource Description Framework (RDF), which provides an abstract
            syntax and semantics for metadata graphs, is a W3C Recommendation
            for publishing graph-based metadata on the Web. The Dublin Core
            Metadata Initiative has based the design of its core architecture
            standards on a graph-like model of resource descriptions, inspired
            by and with a mapping to RDF. The OAI-ORE initiative has built the
            foundations for its compound information objects specification on
            the notion of named metadata graphs. The LUISA EU project has
            developed a toolkit for deploying lightweight, highly-configurable
            metadata editors, also based on metadata graphs.

            In spite of this, vital architectural components are missing or are
            not integrated, preventing this technology from being fully
            exploited across a wide community sharing similar concerns. Because
            of this, the three major initiatives (OAI-ORE, W3C Semantic Web
            Activity, DCMI) are not currently aligned. If they were aligned,
            advances made within any one community could be immediately
            transferrable to all others. For example, the DCMI has made
            important progress towards the formal definition of "application
            profiles", which are application-specific specifications of
            metadata usage, used to set expectations between communicating
            parties and define automated quality control processes for metadata
            exchange. However, because this work has been built on the DCMI
            Abstract Model, and not directly on a graph-based metadata model,
            these important achievements cannot be transferred to the Semantic
            Web or OAI-ORE contexts, where tools and techniques for metadata
            validation are in great demand. Similarly, there is no standard way
            of exposing metadata graphs, of the kind envisioned by the OAI-ORE
            community for the description of compound information objects, or
            of the kind envisioned by the ePrints application profile for the
            description of scholarly works, via the OAI-PMH protocol.

            Therefore, there exists an exciting opportunity to leverage work
            across these initiatives and to bring them into alignment, via the
            provision of key enabling and integrating technologies.

    2. Architecture
        The starting point for the SoDC information architecture is the
        Resource Description Framework (RDF) abstract syntax. The RDF abstract
        syntax provides a foundation for graph-based (meta)data -- data that
        describes things which are related to other things.

        Informally, the RDF abstract syntax can be summarised as follows. A
        graph describes resources, each resource has properties which have
        values. The value of a property can be a URI, a literal or a blank node
        (a.k.a. "anonymous" resource). A literal can be a plain literal or a
        typed literal. A resource can be identified by a URI, or can be
        "anonymous". A property is identified by a URI.

        So, for example, a graph might describe a book titled "Winnie the
        Pooh", created by a person called "A. A. Milne".

    3. Design Goals
        SoDC-XML is a concrete XML syntax for graph-based (meta)data. SoDC-XML
        has the following design goals:
        -- Concrete encoding of the RDF abstract syntax;
        -- Suitable for embedding in (meta)data harvesting protocols, e.g. OAI-PMH;
        -- Constrained by a W3C XML schema, to support basic syntax validation;
        -- Can be constrained by an application-specific schema, to support 
           higher levels of syntax validation.

        SoDC-CL (Constraints Language) is a language for expressing
        application-specific syntax constraints over graph-based (meta)data,
        such as those defined by an "application profile". SoDC-CL has the
        following design goals:
        -- Express constraints over the RDF abstract syntax;
        -- Can be used to automatically generate a concrete syntax validation
           tool, such as a Schematron schema, which can then be used to perform
           application-specific syntax validation of (meta)data encoded in
           SoDC-XML.

-- 
Tom Baker <[log in to unmask]>

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