LC Responses/JR5

From: Jonathan Rees <jar@creativecommons.org> Date: Mon, 26 Jan 2009 16:51:40 -0500 Message-Id: <B4A467D6-9225-4FCD-95AB-02986594A029@creativecommons.org> To: public-owl-comments@w3.org


SSFSS 9.5

"The SameIndividual assertion allows one to state that several individuals are all equal to each other, while the DifferentIndividuals assertion allows for the opposite — that is, to state that several individuals are all different from each other."

If you have several individuals, they can't be equal to each other, since otherwise you'd only have one individual; and there is no need to state that several individuals are different, since otherwise there wouldn't be several of them, there would only be one.

I think what you mean to say is that SameIndividual allows one to say that several individual *expressions* all refer to the same individual, or that several *apparently* different individuals are equal, or something like that.

This is a symptom of a confusion throughout between the document expressions and what they refer to. A class is not an IRI, and yet you say Class := IRI. Now I realize that 'Class' (upper case) is defined formally to be a syntactic thing, and is not at all the same as a class, so while this is not to my taste (I would have called it a 'ClassName', paralleling 'ClassExpression') I can't really object to it. But the attitude is dangerous. I think I already pointed out a problem of this sort in the introduction.

The treatment of "anonymous individuals" is also very confusing. First of all, members of the AnonymousIndividual class are not individuals, they are syntactic things denoting individuals. Second, in what sense are the individuals anonymous? The nodeid sure looks to me as if it is a name for the individual, albeit a local one that is not an IRI. You could take "name" = "nym" as a term of art meaning "IRI", so that nodeids do not qualify as names, but this seems a stretch. Rather than define "name" or "anonymous" technically, I think it would be easier to just create a new technical term for this syntactic category such as 'blank' or 'blank individual name' or 'local name' or 'node id'.

The construction "with anonymous individuals renamed" in section 11 is especially disturbing, since it says directly that anonymous individuals have names. There is similar usage in 3.4.

5.6

"Individuals represent actual objects from the domain being modeled. There are two types of individuals in OWL 2. Named individuals are given an explicit name that can be used in any ontology in the import closure to refer to the same individual. Anonymous individuals are local to the ontology they are contained in."

Because of SameIndividual, a single individual can be both "named" and "anonymous". The error here is confusing the individual with the name of the individual (the Individual). What you mean to say is that individuals can be named (or designated) in either of two ways, using an Individual (or I would say IRI or IndividualName) or using a node id; or neither, or both. Named vs. anonymous is a partition of the syntactic space of Individuals, not of the space of individuals.

Best Jonathan


PeterPatel-Schneider 21:31, 10 February 2009 (UTC)


[Draft Response for LC Comment 50:]

It is quite often common to be a bit sloppy about the distinction between names and whatever they denote or mean, consider, for example, the common use of "the variable x" instead of "the variable named x". Often the loss in precision is gained back in readability. In the interests of gaining this readability, the OWL Functional Syntax generally does not use markers in its syntactic categories to indicate, for example, "ClassName" or "ClassID", instead using just "Class".

Of necessity, this breaks down for individuals. The overall syntactic category in the OWL Functional Syntax is "Individual", which is then divided into "NamedIndividual" and "AnonymousIndividual". The alternative "IndividualName" and "IndividualAnonymousMarker" would have been a reasonable alternative, but would have somewhat conflicted with the usage for other syntactic categories.

As you point out, there are some parts of the document that should be revised so as to not be so confusing.

The WG has decided to make the following modifications in response to your comments:


Section 3.4:

The axiom closure of an ontology O is the smallest set that contains all the axioms from each ontology O' in the import closure of O with all anonymous individuals *standardized* apart — that is, the anonymous individuals from different ontologies in the import closure of O are treated as being different; see Section 5.6.2 for further details.

Section 5.6:

Individuals in the OWL 2 syntax represent actual objects *(semantic individuals)* from the domain being modeled. There are two types of individuals in *the syntax of* OWL 2. Named individuals are given an explicit name that can be used in any ontology ** to refer to the same *semantic* individual. Anonymous individuals *do not have this global name and thus* are local to the ontology they are contained in.

Section 5.6.2:

Special treatment is required in case anonymous individuals with the same node ID occur in two different ontologies. In particular, these two individuals are structurally equivalent (because they have the same node ID); however, they are *not* treated as *identical* in the semantics of OWL 2 (because anonymous individuals are local to an ontology they are used in). The latter is achieved by *standardizing* anonymous individuals apart when constructing the axiom closure of an ontology O: if anonymous individuals with the same node ID occur in two different ontologies in the import closure of O, then one of these individuals MUST be replaced in the axiom closure of O with a fresh anonymous individual (i.e., with an anonymous individual having a globally unique node ID).

Section 5.6.2 Example 2:

In order to ensure that these individuals are treated differently by the semantics they are *standardized* apart when computing the axiom closure of O1 — either _:a5 in O1 is replaced with a fresh anonymous individual, or this is done for _:a5 in O2.

Section 9.5:

OWL 2 supports a rich set of axioms for stating assertions — axioms about individuals that are often also called facts. For clarity, different types of assertions are shown in three separate figures, Figure 18, 19, and 20. The SameIndividual assertion allows one to state that several individuals are all equal to each other *(more precisely, the several different individuals in the syntax denote the same semantic individual)*, while the DifferentIndividuals assertion allows for the opposite — that is, to state that several individuals are all different from each other *(more precisely, that the several different individuals in the syntax are also semantically different)*. The ClassAssertion axiom allows one to state that an individual is an instance of a particular class.

Section 11:

The axiom closure Ax (with anonymous individuals *standardized* apart as explained in Section 5.6.2) of each OWL 2 ontology O MUST satisfy the global restrictions defined in this section. As explained in the literature [SROIQ], this restriction is necessary in order to obtain a decidable language. The formal definition of these conditions is rather technical, so it is split into two parts. Section 11.1 first introduces the notions of a property hierarchy and of simple object property expressions. These notions are then used in Section 11.2 to define the actual conditions on Ax.


The diffs can be found at ..................................

The WG considers this to be an editorial change.

Please acknowledge receipt of this email to <mailto:public-owl-comments@w3.org> (replying to this email should suffice). In your acknowledgment please let us know whether or not you are satisfied with the working group's response to your comment.

Regards, Peter F. Patel-Schneider on behalf of the W3C OWL Working Group


PeterPatel-Schneider 16:01, 19 February 2009 (UTC)

[Response for LC Comment 50:]

Dear Jonathan,

Thank you for your message

 http://lists.w3.org/Archives/Public/public-owl-comments/2009Jan/0052.html

on the OWL 2 Web Ontology Language last call drafts.

It is quite often common to be a bit sloppy about the distinction between names and whatever they denote or mean, consider, for example, the common use of "the variable x" instead of "the variable named x". Often the loss in precision is gained back in readability. In the interests of gaining this readability, the OWL Functional Syntax generally does not use markers in its syntactic categories to indicate, for example, "ClassName" or "ClassID", instead using just "Class".

Of necessity, this breaks down for individuals. The overall syntactic category in the OWL Functional Syntax is "Individual", which is then divided into "NamedIndividual" and "AnonymousIndividual". The alternative "IndividualName" and "IndividualAnonymousMarker" would have been a reasonable alternative, but would have somewhat conflicted with the usage for other syntactic categories.

As you point out, there are some parts of the document that should be revised so as to not be so confusing.

The WG has decided to make the following modifications in response to your comments:


Section 3.4:

The axiom closure of an ontology O is the smallest set that contains all the axioms from each ontology O' in the import closure of O with all anonymous individuals *standardized* apart — that is, the anonymous individuals from different ontologies in the import closure of O are treated as being different; see Section 5.6.2 for further details.

Section 5.6:

Individuals *in the OWL 2 syntax* represent actual objects *(semantic individuals)* from the domain being modeled. There are two types of individuals in *the syntax of* OWL 2. Named individuals are given an explicit name that can be used in any ontology ** to refer to the same *semantic* individual. Anonymous individuals *do not have this global name and thus* are local to the ontology they are contained in.

Section 5.6.2:

Special treatment is required in case anonymous individuals with the same node ID occur in two different ontologies. In particular, these two individuals are structurally equivalent (because they have the same node ID); however, they are *not* treated as *identical* in the semantics of OWL 2 (because anonymous individuals are local to an ontology they are used in). The latter is achieved by *standardizing* anonymous individuals apart when constructing the axiom closure of an ontology O: if anonymous individuals with the same node ID occur in two different ontologies in the import closure of O, then one of these individuals MUST be replaced in the axiom closure of O with a fresh anonymous individual (i.e., with an anonymous individual having a globally unique node ID).

Section 5.6.2 Example 2:

In order to ensure that these individuals are treated differently by the semantics they are *standardized* apart when computing the axiom closure of O1 — either _:a5 in O1 is replaced with a fresh anonymous individual, or this is done for _:a5 in O2.

Section 9.5:

OWL 2 supports a rich set of axioms for stating assertions — axioms about individuals that are often also called facts. For clarity, different types of assertions are shown in three separate figures, Figure 18, 19, and 20. The SameIndividual assertion allows one to state that several individuals are all equal to each other *(more precisely, the several different individuals in the syntax denote the same semantic individual)*, while the DifferentIndividuals assertion allows for the opposite — that is, to state that several individuals are all different from each other. *(More precisely, that the several different individuals in the syntax are also semantically different.)* The ClassAssertion axiom allows one to state that an individual is an instance of a particular class.

Section 11:

The axiom closure Ax (with anonymous individuals *standardized* apart as explained in Section 5.6.2) of each OWL 2 ontology O MUST satisfy the global restrictions defined in this section. As explained in the literature [SROIQ], this restriction is necessary in order to obtain a decidable language. The formal definition of these conditions is rather technical, so it is split into two parts. Section 11.1 first introduces the notions of a property hierarchy and of simple object property expressions. These notions are then used in Section 11.2 to define the actual conditions on Ax.


The diffs can be found at http://www.w3.org/2007/OWL/wiki/index.php?title=Syntax&diff=18157&oldid=18096


The Direct Semantics document mentions standardizing of anonymous individuals, and has been appropriately edited. The diffs can be found at http://www.w3.org/2007/OWL/wiki/index.php?title=Direct_Semantics&diff=18158&oldid=17932

The WG considers these to be editorial changes.

Please acknowledge receipt of this email to <mailto:public-owl-comments@w3.org> (replying to this email should suffice). In your acknowledgment please let us know whether or not you are satisfied with the working group's response to your comment.

Regards, Peter F. Patel-Schneider on behalf of the W3C OWL Working Group

Last modified on 19 February 2009, at 16:01