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Re: differences between OWL 1 and OWL 2

From: Sandro Hawke <sandro@w3.org>
Date: Wed, 01 Apr 2009 15:19:48 -0400
To: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
cc: public-owl-wg@w3.org
Message-ID: <30119.1238613588@ubehebe>
> As far as I know, the changes from OWL 1 to OWL 2 are additions, with
> only a very few exceptions.  The differences could be described as
> follows:

Thanks.  A few clarifications, mostly by offering new wordings that I
find clearer.  (I don't actually know if the claims are true; they just
reword what I think you're saying.)

>   OWL 2 is almost entirely compatible with OWL 1, both syntactically and
>   semantically.
> 
>   The functional syntax for OWL 2 is organized differently than the
>   abstract syntax for OWL 1, but every construct in the OWL 1 abstract
>   syntax has a directly corresponding construct in the OWL 2 functional
>   syntax.

I wasn't thinking we'd include this kind of thing, although maybe it's
helpful.  My concern is with OWL 1 ontologies which will be treated
differently in an OWL 2 reasoner than they were in an OWL 1 reasoner.
That's the "backward compatibility" issue, as I see it.

>   Just as in OWL 1, OWL 2 can handle all RDF graphs.  The vocabulary
>   that is given special meaning in OWL 2 includes the special vocabulary
>   of OWL 1.  However, the use of owl:DataRange is deprecated --
>   rdfs:Datatype should be used instead.

For that last sentence, how about (if true):

    However, we now recommend the use of rdfs:Datatype instead of
    owl:DataRange.  While owl:DataRange can still be used in OWL 2,
    users should avoid it because ...(why?)...

Are there other things you can still do that we're not suggesting not
be done?  Maybe those should be listed separately -- they don't actually
break backward compatibility.

>   The direct semantics for OWL 2 is almost completely compatible with
>   the direct semantics for OWL 1.  The only difference is that
>   annotations are semantics-free in the direct semantics for OWL 2.

add:

    This means that annotations no longer affect the entailments or
    consistancy of an ontology; the fact that they did so in OWL 1 was
    regarded by the OWL Working Group as an error.   

Is there any (helpful) advice we can offer anyone who relied on this
behavior of OWL 1?   This kind of 

>   The RDF-based semantics for OWL 2 is completely compatible with the
>   RDF-based semantics for OWL 1.  Some of the details of this semantics
>   have changed, but the set of inferences are the same.

second sentence, replace with:

    The way the semantics has been specified has changed [to be
    clearer?], but (except for the OWL 2 features), their meaning is the
    same.  This means the entailments of any RDF graph which does not
    use the vocabulary introduced in OWL 2 are exactly the same
    according to the OWL 1 RDF-based semantics and the OWL 2 RDF-based
    semantics.

On the other hand, we might not need to say this, if it can be covered
by a blanket statement (see below).

>   The treatment of importing in RDF documents has changed slightly in
>   OWL 2 if the RDF graphs are to be considered as OWL 2 DL ontologies.
>   In OWL 1, importing happened first, so the entire merged graph was
>   considered as one unit.  In OWL 2, the individual documents are
>   considered separately in most cases.  This means that there are some
>   groups of documents that could form an OWL 1 DL ontology but that do
>   not form OWL 2 DL ontologies.

I'd want some more details or a link to more details here.  (And not
just a link to http://www.w3.org/2007/OWL/wiki/Syntax#Imports but rather
something that explains what I as user migrating to OWL 2 software need
to worry about.)

So, if this is really all there is, then maybe we can have text like
this in Overview:

    With the exception of two minor changes, OWL 2 is backward
    compatible with OWL 1.

    {{EdNote||The Working Group considers these changes to be bug fixes
    and expects them to solve more user problems than they might cause.
    If they cause you any sigificant difficultly, please let us know.}}

    If OWL 1 users are not affected by these specific changes, they do
    not need to change their ontologies when they start using OWL 2
    software.  OWL 2 is defined such that all conformant OWL 2 systems
    will behave just like conformant OWL 1 systems when handling OWL 1
    ontologies.

    The changes between OWL 1 and OWL 2 which are not backward
    compatible are:

       * In the Direct Semantics, annotations no longer have any
         semantics.  They do not affect entailments or consistency. 

       * The treatment of importing in RDF documents has changed
         slightly in OWL 2 if the RDF graphs are to be considered as OWL
         2 DL ontologies. In OWL 1, importing happened first, so the
         entire merged graph was considered as one unit.  In OWL 2, the
         individual documents are considered separately in most cases.
         This means that there are some groups of documents that could
         form an OWL 1 DL ontology but that do not form OWL 2 DL
         ontologies.   For details, see @@@



     -- Sandro
Received on Wednesday, 1 April 2009 19:19:58 GMT

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