Feeds

Access isn’t a relational database

We're all related somehow

Secure remote control for conventional and virtual desktops

Database myths and legends (Part 6) This is a great example of a myth/legend that is both true and false; it all depends on how you define relational.

Ted Codd produced one of the first attempts to define exactly what the term relational Database Management System (DBMS) means. Since Dr. Edgar Codd is regarded as ‘the Father of the Relational Database’, most people assume he knew what he was talking about. He published two articles in Computerworld (14th and 21st October 1985) and in the first he wrote:

“In this paper I supply a set of rules with which a DBMS should comply if it is claimed to be fully relational.”

These rules are often referred to as Codd’s 12 rules, despite the fact that there are 13 of them. Codd numbered them from zero and many people didn’t read the rules, they simply looked at the highest number and assumed that there were 12 - apparently even including Codd, who didn't count Rule 0 and mostly referred to his "12 rules" himself.

The first rule makes one thing perfectly clear:

‘Rule 0: For any system that is advertised as, or claimed to be, a relational data base management system, that system must be able to manage data bases entirely through its relational capabilities.’

In other words, to be considered a relational database engine, the product in question has to obey all of the rules. He then goes on to list what he considers the essential requirements. Not only are the rules relatively stringent, it turned out that one was impossible to fulfil. Rule 6 sounds simple initially:

‘All views that are theoretically updatable are also updatable by the system.’

However, Codd’s expansion of that rule: “Note that a view is theoretically updatable if there exists a time-independent algorithm for unambiguously determining a single series of changes to the base relations that will have as their effect precisely the requested changes in the view” is a logical killer. In1988, H. W. Buff published a paper entitled “Why Codd’s Rule No. 6 Must Be Reformulated” which proved that it is impossible to define such an algorithm precisely.

So, to be relational, an engine has to meet all of the rules and one of those rules has been proved to be impossible to fulfill. Since it is now clear that no database engine can ever be relational, it follows that Access is not relational. QED.

I agree that this is simply an exercise in logic chopping (although I have heard precisely this argument used); however it is also true that some people who work very seriously in this field really do think that none of the mainstream engines are truly relational. Chris Date (Ted Codd’s closest co-worker) has stated in an interview he gave to Tony Williams here that the existing mainstream DBMSs are “all deeply flawed”.

The essential guide to IT transformation

More from The Register

next story
The Return of BSOD: Does ANYONE trust Microsoft patches?
Sysadmins, you're either fighting fires or seen as incompetents now
Munich considers dumping Linux for ... GULP ... Windows!
Give a penguinista a hug, the Outlook's not good for open source's poster child
Intel's Raspberry Pi rival Galileo can now run Windows
Behold the Internet of Things. Wintel Things
Linux Foundation says many Linux admins and engineers are certifiable
Floats exam program to help IT employers lock up talent
Microsoft cries UNINSTALL in the wake of Blue Screens of Death™
Cache crash causes contained choloric calamity
Eat up Martha! Microsoft slings handwriting recog into OneNote on Android
Freehand input on non-Windows kit for the first time
prev story

Whitepapers

Implementing global e-invoicing with guaranteed legal certainty
Explaining the role local tax compliance plays in successful supply chain management and e-business and how leading global brands are addressing this.
Top 10 endpoint backup mistakes
Avoid the ten endpoint backup mistakes to ensure that your critical corporate data is protected and end user productivity is improved.
Top 8 considerations to enable and simplify mobility
In this whitepaper learn how to successfully add mobile capabilities simply and cost effectively.
Rethinking backup and recovery in the modern data center
Combining intelligence, operational analytics, and automation to enable efficient, data-driven IT organizations using the HP ABR approach.
Reg Reader Research: SaaS based Email and Office Productivity Tools
Read this Reg reader report which provides advice and guidance for SMBs towards the use of SaaS based email and Office productivity tools.