Letters to the editor

PostgreSQL and relational.

In reference to your e-mail on the subject of PostgreSQL not being relational,
would you mind specifying exactly which of E F Codd's 12 rules of the
relational model PostgreSQL breaks? Using SQL as the language to access a
RDBMS does not invalid the relational model used by that RDBMS. Show me the
rule(s) broken specifically by PostgreSQL itself, not by SQL in general.
 
PostgreSQL meets the qualifications for a relational system as defined by E F
Codd and C J Date. Having read Date's work, I find it amusing that you would
quote from a site which prominently features C J Date as a contributor.
 
You need to take MySQL to task for truly not being relational according to
Codd's 12 rules. :-)
--
Lamar Owen
WGCR Internet Radio
1 Peter 4:11

Comments (none posted)

Re: PostgreSQL and relational.

Lamar Owen escreveu:
 
 > In reference to your e-mail on the subject of PostgreSQL not being
 > relational, would you mind specifying exactly which of E F Codd's 12
 > rules of the relational model PostgreSQL breaks?
 
        EF Codd's 12 rules aren't all that is to the relational
model. In fact, he expanded these 12 to 40 rules in his 1.990 book
_The_Relational_Model_for_Database_Management.
 
        But furthermore, if you care to read Christopher J Date's
1.999 _An_Introduction_to_Database_Systems_ you will see that the
relational model comprises some basic elements and some principles.
 
        The basic element is the domain, or data type. PostgreSQL
does not really enforces domains because it accepts NULL, which by
definition is not part of any domain. Thus the triplet domain, name
and value called attribute breaks down, and so the tuple -- because it
represents a proposition, and a proposition with missing information
is another proposition, not the one declared in the relation's header
--, and so also the relation breaks down.
 
        Furthermore, the relation is a set, not a bag. A bag
accepts duplicates, but not a relation. So because PostgreSQL does
not enforce the necessity of declaring a candidate key for each and
every table, its tables are not necessarily relations, but quite
possibly and commonly bags of not tuples as shown above, but simply
rows.
 
        Also, the first principle is The Information Principle, where
all the database must be represented by data. Object IDs violate
this, with serious consequences about data independence, which by the
way is necessary to another relational model sine qua non, namely the
separation between user, logical and physical schemas. Also not
properly supported by PostgreSQL.
 
 
 > Using SQL as the language to access a RDBMS does not invalid the
 > relational model used by that RDBMS. Show me the rule(s) broken
 > specifically by PostgreSQL itself, not by SQL in general.
 
        I am not so familiar with the PostgreSQL dialect, but for what
I've seen it does little to nothing to address SQL shortcomings that
disqualify it as an implementation of the relational model.
 
 
 > PostgreSQL meets the qualifications for a relational system as
 > defined by E F Codd and C J Date. Having read Date's work, I find
 > it amusing that you would quote from a site which prominently
 > features C J Date as a contributor.
 
        Perhaps you should read Date more carefully. When he writes
about SQL, he can barely disguise the sarcasm.
 
 
 > You need to take MySQL to task for truly not being relational
according to
 > Codd's 12 rules. :-)
 
        Believe me, I do take MySQL to task, it isn't even up to SQL
level.
 
        But I do think SQL itself is to blame, so until
someone creates a D interface as defined by Date and Darwen to
PostgreSQL or some other DBMS, we're stuck hopelessly behind the
times, more precisely 30 years late as measured by Codd's work
publications.
 
        To be precise, there is an implementation of a valid D, but
it's unfortunately proprietary & expensive:
http://www.alphora.com/tiern.asp?ID=DATAPHOR.
 
 
--
  _
/ \ Leandro Guimarães Faria Corsetti Dutra +41 (21) 216 15 93
\ / http://homepage.mac.com./leandrod/ fax +41 (21) 216 19 04
  X http://tutoriald.sf.net./ Orange Communications CH
/ \ ASCII Ribbon Campaign against HTML email +41 (21) 216 15 93

Comments (1 posted)

Lindows and the sources

>From
http://help.lindows.com/cgi-bin/visitors.cfg/php/enduser/std_adp.php?p_faqid=23
 
> Lindows.com respects all applicable licensing and is proud to be
> a strong supporter of the Open Source community
 
...linking to http://www.lindows.com/lindows_products_license.php
 
> Such software programs may be licensed (or sublicensed) to the user
> under the GNU General Public License and other similar open source
> license agreements which, among other rights, permit the user to
> copy, modify and redistribute certain programs, or portions thereof,
> and have access to the source code.
 
> You may find the licenses and source code to these open source
> third-party programs here:
 
> http://www.debian.org
 
> http://www.kde.org
 
> http://www.winehq.com
 
> Lindows.com is pleased to be a proud supporter of these initiatives
> through conference sponsorships, financial support, and code
> development. All code changes made by Lindows.com to the above
> products are sent back to these organizations and/or will be made
> available for download here. (Keep in mind that LindowsOS hasn't
> even released a Beta version of LindowsOS, so the source code is
> very unstable and changing continually.)
 
1. WalMart is shipping LindowsOS on its PCs.
 
2. According to the GPL, Lindows _itself_ is responsible for
   distributing the source for any binaries it distributes, _not_
   the organisations Lindows link to.
 
3. There is no provision for source _following_ binaries: in order
   for binaries derived from GPLed programs to be distributed,
   Lindows must make the source available _before_ or _with_
   the binaries.
 
4. There are no exceptions in the GPL for `unstable and changing'.
 
5. The sources at http://net2.com/lindows/source/ do not appear to
   be complete, in particular most of the leaves on this directory
   tree contain only package descriptions and do not appear to
   reflect any substantial changes that Lindows may have made.
 
6. Other GPL distributors, notably the easy-to-use Mandrake corporate
   and purist not-for-profit Debian organisation, have no trouble
   making sources available with or before binaries.
 
Please explain.
 
--
CyberKnights Modern tools, traditional dedication.
+61-409-655-359 http://www.cyberknights.com.au/
 
linux.conf.au 2003 The Australian Linux Technical Conference
http://conf.linux.org.au/ 22-25 January 2003 in Perth, Western Australia

Comments (none posted)