- From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
- Date: Wed, 26 Sep 2001 13:26:05 -0400
- To: phayes@ai.uwf.edu
- Cc: www-rdf-logic@w3.org
Good job. However, I see several problems in the document. Some of these
I view as significant.
1/ The document does not sufficiently pin down the relationship between
literal values and resources.
The model theory does not require that literal values and resources be
disjoint. Further, an RDF graph, as defined in Section 0.2, allows the
head of edges to be labeled with literals. This means that there is no
significant difference between resources and literal values, nor between
URIs and literals.
The document, as it will probably be read, strongly suggests that
literal values and resources are disjoint. In Section 1.3, IEXT is a
map into IR x (IR u LV), which will probably be read as requiring that
LV and IR be disjoint.
I think that the document needs to come down firmly on one side or the
other. Either it has to state that it is extending RDF to allow
literals to be the subject of predicates, or it has to exclude the
possibility of literals being the subject of predicates.
2/ The model theory does not assign meaning to RDF graphs. Instead it
assigns meaning to RDF graphs with an extra, nowhere-defined attribute
on edges. If this is supposed to be a model theory, then it should be
rigorous, and not have any undefined junk floating around.
3/ The model theory maps literals into literal values and URIs into
resources when it should be mapping nodes.
4/ The model theory breaks down for edges whose edge label does not map
into a property as IEXT is only defined on properties.
5/ The model theory allows multiple URIs to map to the same resource. I
applaud this feature of the model theory, but it should be noted in the
document outside of examples.
6/ The definitions of IEXT and IS should use the same notation.
7/ The mapping of unlabeled nodes is to the ``domain'' of interpretations,
but interpretations don't have domains. Later on the mapping for
unlabeled nodes is restricted to map to IR, which makes sense.
8/ In the model theory for RDFS, there is the requirement that all literals
have rdf:type of LITERAL. This now requires that literals be allowed in
the subject position of predicates, which is forbidden in M&S and in the
document as probably being read, but not forbidden in the model theory
itself, although it has the effect of making all literals be resources.
9/ The model theory for RDFS is missing the requirement that the vocabulary
contain all the RDFS ``pre-defined'' URIs.
10/ The model theory for RDFS is confusing with respect to the status of
ICEXT. ICEXT is not included in an interpretation, but appears
prominently in the interpretation conditions. Now it is not strictly
necessary to have ICEXT be part of an RDFS interpretations, as implied
in the document, but if so, then it would be much better to write the
conditions without ICEXT (and also remove the condition that becomes
vacuous).
11/ The RDFS conditions are missing the fact that many ``pre-defined'' URIs
belong to IC.
12/ The RDFS conditions are missing the range restriction on rdf:type.
Without this restriction, ICEXT is not simply a convenience nor is
rdfs:Resource an rdfs:Class in the model theory.
13/ Many domain and range properties are missing from the RDFS
interpretation conditions.
14/ The RDFS schema-closure rule 1a has the effect of making all literal
values be resources as all literal values have an rdf:type property
because they are in the class extension of rdfs:Literal. This is valid
in the RDFS model theory, as all literals must be resources there, but
is probably not expected.
15/ The RDFS schema-closure rule 1c also has the effect of making most
literal values be resources. This is a valid rule, because all
literals are already resources, but is probably not expected.
16a/ Because of the missing domain and range properties the RDFS
schema-closure rules 9a and 9b, are not valid. The RDFS schema-closure
rules are only valid because only properties have IEXT mappings.
16b/ Because of the missing range property on rdf:type, RDFS schema-closure
rule 7 is invalid.
16c/ Because of the missing range property on rdf:type, all resources are
subclasses of rdfs:Resource.
16.../ There are probably other consequences of the missing domain and
range properties.
17/ Because of the complexity of RDFS, I won't believe the Schema Lemma
until I see a completely worked out proof.
There is a typo in Figure 1. It should say IEXT(1) instead of IEXT(I).
There is a typo in the RDFS conditions. They should say
IEXT(I(rdfs:subPropertyOf)) instead of IEXT(rdfs:subPropertyOf).
Received on Wednesday, 26 September 2001 13:25:52 UTC