Dear John, Leo, Matthew and William (01)
>Yes, indeed, Matthew, but we need to clarify things in this forum, not confuse
>people, or give them false information. When the external programming language
>code surrounding a relational database essentially creates its own semantics
>in procedural code (which is extensive, I admit) for a given database, it is
>not the same as saying that the relational model of RDBs is open world. It's
>not.
> (02)
To further clarify I would like to add that CWA is necessary to allow efficient
reasoning which is sound complete and decidable. Codd's relational algebra
requires CWA included in highly expressive FOL such as dialects of SQL.
Semantic Web challenges can be understood as various ways to remove CWA while
retaining some properties RDBs, hence Web of relations, but without powerful
relational algebra. This means that some times Semantic Web languages requires
partial closing of the open world assumption to allow feasible reasoning over
LOD. This is often a source of confusion about query with SQL vs SPARQL, for
example. (03)
>Thanks,
>Leo (04)
>
>From: ontolog-forum-bounces@xxxxxxxxxxxxxxxx
>[mailto:ontolog-forum-bounces@xxxxxxxxxxxxxxxx] On Behalf Of Matthew West
>Sent: Saturday, January 19, 2013 7:05 PM
>To: Ontolog-Forum
>Subject: Re: [ontolog-forum] Knowledge graphs by Google and Facebook
>
>
>Dear Leo,
>DBMS query engines are generally closed world, but the applications that use
>them are not necessarily closed world but may reinterpret the closed world
>results.
>Regards
>Matthew
>On Jan 19, 2013 10:31 PM, "Obrst, Leo J."
><lobrst@xxxxxxxxx<mailto:lobrst@xxxxxxxxx>> wrote:
>Relational databases are nearly always under the closed world assumption.
>There may be exceptions, but they are few. Similarly, logic programming in
>general is under closed world assumption, though there are variants
>(well-formed semantics) and answer set programming (which can have negation
>operators under both CWA and OWA).
>
>Thanks,
>Leo
>
>>-----Original Message-----
>>From:
>ontolog-forum-bounces@xxxxxxxxxxxxxxxx<mailto:ontolog-forum-bounces@xxxxxxxxxxxxxxxx>
> [mailto:ontolog-forum-<mailto:ontolog-forum->
>>bounces@xxxxxxxxxxxxxxxx<mailto:bounces@xxxxxxxxxxxxxxxx>] On Behalf Of John
>F Sowa
>>Sent: Saturday, January 19, 2013 3:45 PM
>>To: [ontolog-forum]
>>Subject: Re: [ontolog-forum] Knowledge graphs by Google and Facebook
>...
>>
>>SQL and SPARQL can be used for either open world or closed world
>>databases. It is true that nearly all the stuff on the WWW is open
>>world, but many, if not most relational DBs are also open world.
>>
>
>
>
>
>
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