This document summarizes the common understanding of the RDF Core Working Group (further referred to as WG) with regards to the theoretical foundation for datatyping of literal values and serves as a basis of definition, discussion, and comparison of all proposed schemes for achieving a complete datatyping solution which are to be considered by the WG.
Many other WG members not listed above have helped to shape this
document.
The desiderata (which may or may not constitute
requirements) are detailed separately in [link to Graham's
desiderada doc].
(@@@ Or should Graham's doc be merged back into here? ;-)
[Definition:] A
datatype mapping is a set of pairs whose first element belongs
to the value space of the datatype, and the second element belongs to the lexical
space of the datatype.
A datatype mapping satisfies the following properties:
(@@@ is the second condition necessary? Should we distinguish between
partial and complete datatype mappings?)
Table of Contents
1 Introduction
1.1 Scope
The RDF Core Working Group is not chartered to develop a separate data
typing language that duplicates facilities provided by XML Schema data
types (see RDF Core WG Charter).
1.2 Desiderata for RDF Datatyping
1.3 Deliverables of RDF Datatyping
2 Type System
The conceptual framework for datatyping presented in this document is
based on the type system defined in the "XML Schema Part 2: Datatypes"
[XSD]. This section explains how the relevant
terms and concepts defined in [XSD] are expressed
using the model-theoretic semantics for RDF defined in the "RDF Model
Theory Working Draft" [RDF MT].
2.1 Datatype mapping
[XSD] defines a datatype as a 3-tuple,
consisting of a) a set of distinct values, called its value
space, b) a set of lexical representations, called its lexical
space, and c) a set of facets that characterize properties
of the value space, individual values or lexical terms. [XSD] implicitly assumes a fourth component, which we
call datatype mapping, to be part of the datatype.
Lexical space: {"0", "1", "true", "false"}
Datatype mapping: {<T, "true">, <T, "1">, <F, "0">, <F, "false">}
2.2 Canonical datatype mapping
As specified in [XSD], a canonical lexical
representation is a set of elements from the lexical space of a datatype
such that there is a one-to-one mapping
between elements in the canonical lexical representation and elements in
the value space. This mapping is referred to as canonical datatype
mapping.
[Definition:] A canonical datatype mapping is a subset of a datatype mapping that establishes a one-to-one correspondence between elements in the canonical lexical representation and elements in the value space.
[Definition:] A datatyping scheme is a convention for representing and using datatypes in RDF.
A datatyping scheme describes how
[RDF MT] explains the fundamental model-theoretic concepts like interpretation, universe, extension etc. used for interpreting the semantics of RDF graphs. This document assumes familiarity with these basic concepts, as likely do all datatyping scheme proposals based on this document.