Encoding schemes

2007-03-13

In the current DCAM [7], "vocabulary encoding scheme" is defined as follows: 

    vocabulary encoding scheme (Proposed URI: http://purl.org/dc/dcam/VocabularyEncodingScheme)

    An enumerated set of resources.

In the current DCAM [7], "syntax encoding scheme" is defined as follows: 

    syntax encoding scheme (http://www.w3.org/2000/01/rdf-schema#Datatype)

    A set of strings and an associated set of rules that
    describe a mapping between that set of strings and a set
    of resources. The mapping rules may define how the string
    is structured (for example DCMI Box) or they may simply
    enumerate all the strings and the corresponding resources
    (for example ISO 3166).

According to http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/#section-Datatypes:

    5. Datatypes (Normative)

    The datatype abstraction used in RDF is compatible with
    the abstraction used in XML Schema Part 2: Datatypes
    [XML-SCHEMA2].

    A datatype consists of a lexical space, a value space
    and a lexical-to-value mapping.

    The lexical space of a datatype is a set of Unicode
    [UNICODE] strings.

    The lexical-to-value mapping of a datatype is a set of
    pairs whose first element belongs to the lexical space
    of the datatype, and the second element belongs to the
    value space of the datatype:

        * Each member of the lexical space is paired with
        (maps to) exactly one member of the value space.

        * Each member of the value space may be paired with
        any number (including zero) of members of the lexical
        space (lexical representations for that value).

    A datatype is identified by one or more URI references.

    RDF may be used with any datatype definition that conforms
    to this abstraction, even if not defined in terms of
    XML Schema.

    Certain XML Schema built-in datatypes are not suitable for
    use within RDF. For example, the QName datatype requires a
    namespace declaration to be in scope during the mapping,
    and is not recommended for use in RDF. [RDF-SEMANTICS]
    contains a more detailed discussion of specific XML Schema
    built-in datatypes.

    Note: When the datatype is defined using XML Schema:

         * All values correspond to some lexical form, either
         using the lexical-to-value mapping of the datatype
         or if it is a union datatype with a lexical mapping
         associated with one of the member datatypes.

         * XML Schema facets remain part of the datatype and
         are used by the XML Schema mechanisms that control
         the lexical space and the value space; however,
         RDF does not define a standard mechanism to access
         these facets.

         * In [XML-SCHEMA1], white space normalization
         occurs during validation according to the value of
         the whiteSpace facet. The lexical-to-value mapping
         used in RDF datatyping occurs after this, so that
         the whiteSpace facet has no effect in RDF datatyping.

In Manzanillo [1], we agreed on the following categorization of 
existing encoding schemes:

-- Syntax encoding schemes

   http://purl.org/dc/terms/Box
   http://purl.org/dc/terms/Period
   http://purl.org/dc/terms/Point
   http://purl.org/dc/terms/ISO3166   [2] - previously considered VES
   http://purl.org/dc/terms/ISO639-2  [3] - previously considered VES
   http://purl.org/dc/terms/RFC1766   [4]
   http://purl.org/dc/terms/RFC3066   [5] 
   http://purl.org/dc/terms/URI
   http://purl.org/dc/terms/W3CDTF

-- Vocabulary encoding schemes

   http://purl.org/dc/terms/DCMIType
   http://purl.org/dc/terms/DDC
   http://purl.org/dc/terms/IMT       [6]
   http://purl.org/dc/terms/LCC
   http://purl.org/dc/terms/LCSH
   http://purl.org/dc/terms/MESH
   http://purl.org/dc/terms/NLM
   http://purl.org/dc/terms/TGN
   http://purl.org/dc/terms/UDC

REFERENCES

[1] http://dublincore.org/usage/minutes/2006/2006-10-01.meeting-notes-manzanillo.html
[2] http://www.iso.org/iso/en/prods-services/iso3166ma/02iso-3166-code-lists/list-en1.html 
[3] http://lcweb.loc.gov/standards/iso639-2/langhome.html
[4] http://www.ietf.org/rfc/rfc1766.txt
[5] http://www.ietf.org/rfc/rfc3066.txt
[6] http://www.iana.org/assignments/media-types/
[7] http://dublincore.org/documents/2007/02/05/abstract-model/


2009-01-29: Changed usageboard/log URIs to usage/minutes URIs.