Redland Notes - RDF and RDF Schema Concepts Reference

by Dave Beckett

$Date: 2001/04/24 14:01:51 $ - Changes

1. Introduction

This document was created to aid me in writing the RDF parser for Redland. I needed to know the answer this question:

What are the XML-namespaced concepts that are defined in RDF Model and Syntax (M&S)[RDF] and RDF Schema (RDFS)[RDFS]?

This was required so that I could guarantee I was providing complete coverage of all legal RDF syntax and doing so correctly in all cases. In order to do this I compiled a table of what XML-namespaced concepts were defined in RDF and RDF Schema. Several additional properties of the concepts also needed to be recorded in order to complete the work:

The type(s) of the concept (rdf:type) if any
Sub-classing information (rdfs:subClassOf) - which implies the type is a rdfs:Class
If it has a meaning in the XML syntax as an element name
If it has a meaning in the XML syntax as an attribute name

(I could have extended this to other relevant [RDFS] properties - rdfs:range and rdfs:domain seem likely)

I give references to where I have found the answers to these questions, referencing only the [RDF] and [RDFS] documents.

Comments and corrections are welcome

Dave Beckett

2. Terminology

Sx.y: [RDF] section x.y
FM 5.x: Rule 5.x in [RDF] section 5. Formal Model for RDF
FG 6.x - n: Production 6.x named n in [RDF] section 6. Formal Grammar for RDF.
BAS1: Use of the M&S basic abbreviation syntax form 1 allowing "properties that are not repeated within a Description and where the values of those properties are literals" to be used as attributes of the Description element.

3. RDF Model and Syntax Concepts

Table 1 contains the concepts defined in the [RDF] supplemented by the type and sub-classing declarations made in [RDFS].

Table 1: RDF Model and Syntax concepts
Concept	rdf:type	rdfs:subClassOf	Has a defined meaning as an Element	Has a defined meaning as an Attribute	Notes
rdf:Seq	1. rdfs:Resource and not rdf:Property (FM 5.10) 2. rdfs:Class (RDFS)	rdfs:Container	1. YES (FG 6.25 - sequence) 2. YES (FG 6.13 - typedNode)	NO
rdf:Bag	1. rdfs:Resource and not rdf:Property (FM 5.10) 2. rdfs:Class (RDFS)	rdfs:Container	1. YES (FG 6.26 - bag) 2. YES (FG 6.13 - typedNode)	NO
rdf:Alt	1. rdfs:Resource and not rdf:Property (FM 5.10) 2. rdfs:Class (RDFS)	rdfs:Container	1. YES (FG 6.27 - alternative) 2. YES (FG 6.13 - typedNode)	NO
rdf:Property	1. rdfs:Resource (FM 5.3) 2. rdfs:Class (RDFS)	rdfs:Resource	YES (FG 6.13 - typedNode)	NO
rdf:Statement	1. rdfs:Resource and not rdf:Property (FM 5.7) 2. rdfs:Class (RDFS)	rdfs:Resource	YES (FG 6.13 - typedNode)	NO	Only use mentioned is as the object of rdf:type in a reified statement (S4.1)
rdf:object	rdf:Property (FM 5.8)	None	YES (S4.1, FM 5.8 - is a rdf:Property)	YES (BAS1)
rdf:predicate	rdf:Property (FM 5.8)	None	YES (S4.1, FM 5.8 - is a rdf:Property)	YES (BAS1)
rdf:subject	rdf:Property (FM 5.8)	None	YES (S4.1, FM 5.8 - is a rdf:Property)	YES (BAS1)
rdf:type	rdf:Property (FM 5.5)	None	YES (FG 6.11 - typeAttr, S4.1, FM 5.5 - is a rdf:Property)	YES (BAS1)
rdf:value	rdf:Property (S7.3)	None	YES (S2.3 - Qualified Property Values, S7.3 example - is a rdf:Property)	YES (BAS1)
rdf:li	None (syntax)	None (syntax)	YES (FG 6.29 - referencedItem, FG 6.30 - inlineItem)	NO (S3.2 - "is a convenience element") YES - `rdf:li` matches FG 6.12 - propertyElt and FG 6.13 - typedNode
rdf:_n / _n where n is an integer >0	rdf:Property (FM 5.11)		YES (S3.1 - is a "membership property")	YES (FG 6.31 - memberAttr, BAS1)
rdf:RDF	None (syntax)	None (syntax)	YES (FG 6.1 - RDF)	NO
rdf:Description	None (syntax)	None (syntax)	YES (FG 6.2 - obj, FG 6.3 - description)	NO
rdf:about / about	None (syntax)	None (syntax)	NO	YES (FG 6.7 - aboutAttr)
rdf:aboutEach / aboutEach	None (syntax)	None (syntax)	NO	YES (FG 6.8 - aboutEachAttr)
rdf:aboutEachPrefix / aboutEachPrefix	None (syntax)	None (syntax)	NO	YES (FG 6.8 - aboutEachAttr)
rdf:ID / ID	None (syntax)	None (syntax)	NO	YES (FG 6.6 - idAttr)
rdf:bagID / bagID	None (syntax)	None (syntax)	NO	YES (FG 6.9 - bagIdAttr)
rdf:resource / resource	None (syntax)	None (syntax)	NO	YES (FG 6.18 - resourceAttr)
rdf:parseType / parseType	None (syntax)	None (syntax)	NO	YES (FG 6.32 - parseLiteral, FG 6.33 - parseResource)

4. RDF Schema Concepts

Table 2 contains the concepts defined in [RDFS].

Table 2: RDF Schema concepts
Concept	rdf:type	rdfs:subClassOf (all from RDF Schema definitions)	Has a defined meaning as an Element	Has a defined meaning as an Attribute
rdfs:Class	rdfs:Class	rdfs:Resource	YES (FG 6.13 - typedNode)	NO (cannot take literal values)
rdfs:ConstraintProperty	rdfs:Class	1. rdfs:ConstraintResource 2. rdf:Property	YES (FG 6.13 - typedNode)	NO (cannot take literal values)
rdfs:ConstraintResource	rdfs:Class	rdfs:Resource	YES (FG 6.13 - typedNode)	NO (cannot take literal values)
rdfs:Container	rdfs:Class	rdfs:Resource	YES (FG 6.13 - typedNode)	NO (cannot take literal values)
rdfs:ContainerMembershipProperty	rdfs:Class	rdf:Property	YES (FG 6.13 - typedNode)	NO (cannot take literal values)
rdfs:Literal	rdfs:Class	None	YES (FG 6.13 - typedNode)	NO (cannot take literal values)
rdfs:Resource	rdfs:Class	None	YES (FG 6.13 - typedNode)	NO (cannot take literal values)
rdfs:range	1. rdfs:ConstraintProperty 2. rdf:Property (because rdfs:ConstraintProperty is rdfs:subClassOf rdf:Property) 3. rdfs:ConstraintResource (because rdfs:ConstraintProperty is rdfs:subClassOf rdfs:ConstraintResource)	None	YES (FG 6.12 - propertyElt)	NO (cannot take literal values)
rdfs:domain	1. rdfs:ConstraintProperty 2. rdf:Property (because rdfs:ConstraintProperty is rdfs:subClassOf rdf:Property)	None	YES (FG 6.12 - propertyElt)	NO (cannot take literal values)
rdfs:isDefinedBy	rdf:Property	None	YES (FG 6.12 - propertyElt)	NO (cannot take literal values)
rdfs:label	rdf:Property	None	YES (FG 6.12 - propertyElt)	YES (BAS1)
rdfs:comment	rdf:Property	None	YES (FG 6.12 - propertyElt)	YES (BAS1)
rdfs:seeAlso	rdf:Property	None	YES (FG 6.12 - propertyElt)	NO (cannot take literal values)
rdfs:subClassOf	rdf:Property	None	YES (FG 6.12 - propertyElt)	NO (cannot take literal values)
rdfs:subPropertyOf	rdf:Property	None	YES (FG 6.12 - propertyElt)	NO (cannot take literal values)

Conclusions

Some things I've found from the above analysis:

Container concepts match two grammar productions (we already knew this)
Container concepts have a rdf:type but that was only defined in RDF Schema as rdfs:Class. RDF M&S just said: "resource and not property"
rdf:li is just syntax, and has no defined meaning as an attribute. However it does match the propertyElt and typedNode productions so can be considered to be a rdf:property
rdf:value is not defined in the formal grammar or formal model but does have a definition in S2.3 where it is defined as a property.
The schema in the RDFS document contains extra not-needed rdf:type statements.
rdfs:ConstraintProperty is the only class that is a subclass of two other classes. This also has the side effect of showing that the RDF type system is quite unconstrained, in this case has no restrictions on multiple inheritance. RDF schemas does not mention inheritance at all despite it saying the "RDF Schema type system is similar to the type systems of object-oriented programming languages such as Java" in section 2.1
Many concepts have no defined meaning as attributes in the syntax

References

[RDF] Model and Syntax W3C Recommendation at http://www.w3.org/TR/REC-rdf-syntax, 22 February 1999.

[RDFS] RDF Schema W3C Candidate Recommendation at http://www.w3.org/TR/2000/CR-rdf-schema-20000327, 27 March 2000.

Changes

2001-04-24

Added rdfs:ConstraintResource as 3rd type of rdfs:range - expanding the subclassing in the table.

2001-01-17

Expanded comment about rdfs:ConstraintProperty being subclass of two classes. Explained RDFS does not restrict this; i.e. has no position on inheritance.

Added reference to prose in S2.3 where rdf:value is defined.

2001-01-12

Added rdf:li as propertyElt, typedNode

Added conclusions section based on the comments I made in my email announcing this document.

Changed the title to "RDF and RDF Schema Concepts Reference"

Validate me