After 23+ years DBDebunk.com has undergone a slight refresh. Here is an outline of the changes.

1. The BOOKS and PAPERS are now unified into one PUBS page from which my papers and self-published books can be ordered. There are two paper series:

• Understanding the Real RDM: reviews and analysis of some Codd's published papers 1969-85 in the spirit of McGoveran re-interpretation of his work--distinct from that dominant in the industry.
• Practical Database Foundations: shorter papers about narrower aspects of the RDM that are abused, misused and ignored in the industry.

Some papers will be brought up to date/re-written and new ones will be published.

2. The recommended books links from the BOOKS page have been moved to the LINKS page.

3. The FUNDAMENTALS page was replaced by a SEARCH page that contains a newly compiled data and relational fundamentals comprehensive dictionary of terms to be maintained on a regular basis. It includes abbreviations/acronyms to be used as labels for searching. Use the page as a reference in conjunction with the labels to compensate partially for a limitation of the Blogger labels facility.

4. Labels now exist only for the search terms that have known abbreviations  or acronyms. The SEARCH page should be used to identify which terms have labels and those that do not must be used with the Blogger search facility (see details on ABOUT page).

Any problems, comments, suggestions, questions, or support are welcome--drop me an email.

 

 

 

 

“A set is an identification of zero or more objects (elements, entities, depending on context) that can be referred to as a group by name (usually a symbol) and which are drawn from some pre-defined universe of objects. Such objects are then said to be the members of the set. The set members have one or more properties in common. It is, however, possible that the sole defining property of a set can be simply that the definer of a set has explicitly designated as members certain (one or more) objects that do not share any properties, so the only property shared by the set members is the designation property (DP) -- each member then has the property of having been designated member of the set. More explicitly, for any set, an assertion of set membership has definitional priority over the necessity of any other properties being shared among the members.” --David McGoveran

Thus, members of a set are "drawn from some pre-defined universe of objects" on the basis of shared properties (that define their type and are required for set membership) -- if nothing else, at least a designation property (DP). These properties distinguish members of the set from those in the universe that are not.

Note: This a revision of an earlier post

RDM is an application to database management of mathematical relation theory (MRT) consistent with simple set theory (SST) expressible in first order predicate logic (SST/FOPL) that is used to formalize symbolically conceptual models of reality as logical models for database representation.

In RDM a domain can "appear" in multiple relations: the domain represents an abstract property, attributes defined on it represent that property in contexts of specific entity groups that relations represent. For example, attribute SALARY in relation EMPLOYEES represents the property represented by domain MONEY in the context of entities of type Employee and attribute BUDGET in relation DEPARTMENTS represents it in the context of entities of type Department.

Note: "Then & Now" (t&n) is a new version of what used to be the "Oldies but Goodies" (OBG) series. To demonstrate the superiority of a sound theoretical foundation relative to the industry's fad-driven "cookbook" practices, as well as the disregarded evolution/progress of RDM, I am re-visiting my old debunkings, bringing them up to the current state of knowledge. This will enable you to judge how well arguments have held up and realize the increasing gap between industry stagnation --  and scientific progress.

Then

“I am an application developer who is competent in SQL and have designed some small-scale schemas that have gotten the job done. I came to your website seeking enlightment on the issue of whether it is better to use strings to represent attributes (I believe these are called "speaking keys"), or to use integers and key them to a list of strings. I see that you are avidly pro-normalization, but I'm not even sure if this is a normalization issue. Here is a quote from a web site that captures my gut feeling. I hope you can comment or point me to an article that presents your view of the matter.

Many popular database tools make it very easy to create some sort of arbitrary numeric sequence for your primary keys. Be careful not to use these to excess. If you have are designing a music catalog system, it is definitely not useful to create a lot of arbitrary codes for music classification. There is unlikely to be much benefit in designating "1" to stand in for "Jazz", 2 for "Rock", 3 for "Classical" and 4 for "Latin Jazz" in an application. Why not just use the word "Jazz" for "Jazz" and use "Rock" to stand for "Rock"? It is certainly easier to remember. It also means that you won't have to lookup the value of 1 to see that it stands for "Jazz".”

Note: In "Setting Matters Straight" posts I debunk online pronouncements that involve fundamentals which I first post on LinkedIn. The purpose is to induce practitioners to test their foundation knowledge against our debunking, where we explain what is correct and what is fallacious. For in-depth treatments check out the POSTS and our PAPERS, LINKS and BOOKS (or organize one of our on-site/online SEMINARS, which can be customized to specific needs). Questions and comments are welcome here and on LinkedIn.

Q: “Does anyone have an alternative solution to the issue where multiple nulls are allowed in the same column for a unique index containing that column? I have a number of such nullable columns and unique index combinations in my database schema and I'm trying to avoid having to create additional generated as columns for each case.”

A: “null<>null so the problem's built into unique columns, perhaps the columns need to become non-nullable?”

“Some attributes in a tuple are not meant to be part of any relationship so people are safe to populate such relationshipless attributes with a Null when needed. Just an example, how about the famous MailAddressSecondLine attribute describing the optional second line of a mail address? You can populate it if needed or you can leave it with no value a.k.a. Null if you have nothing to put in there.”

“So, when YOU create an address table, do you have a "second address" line or do you normalize it? Enquiring minds want to know.”

“You are asking how I would implement optional parts of an address within the limitations of a fixed set of numbered address line attributes? If an address has fewer lines than there are attributes then I'd populate the extra lines with zero-length strings. Null wouldn't be appropriate because all the parts of the address are known and present and using null would give undesirable results. For example if you compare all the parts of an address in a join or subquery you ought to expect two identical addresses to be returned as equivalent, but that wouldn't work if you start adding nulls into addresses.”

We have discussed extensively the problems with and solution to the treatment of missing data in relational databases:

Note: In "Setting Matters Straight" posts I debunk online pronouncements that involve fundamentals which I first post on LinkedIn. The purpose is to induce practitioners to test their foundation knowledge against our debunking, where we explain what is correct and what is fallacious. For in-depth treatments check out the POSTS and our PAPERS, LINKS and BOOKS (or organize one of our on-site/online SEMINARS, which can be customized to specific needs). Questions and comments are welcome here and on LinkedIn.

 

“As I have said many times, if the original relational model had been based on predicate logic and also the semantics and rules of definitions we'd all be better off now. It wasn't. Full stop.”

--Ronald Ross, LinkedIn.com

Assessing such arguments normally requires clarification of what exactly is meant by "the relational model". Ross does refer specifically to the "original" -- which we take to mean that introduced by Codd in 1969-70 -- but given the massive misuse and abuse in the industry, perceptions of it may well be corrupted (Nobody Understands the Relational Model Semantics, Relational Closure and Database Correctness).  Moreover, there are many predicate logic (PL) systems and many ways of categorizing them (1st vs n-th order being only one way) -- we assume Ross means RDM is based on none.

Note: "Then & Now" (t&n) is a new version of what used to be the "Oldies but Goodies" (OBG) series. To demonstrate the superiority of a sound theoretical foundation relative to the industry's fad-driven "cookbook" practices, as well as the disregarded evolution/progress of RDM, I am re-visiting my old debunkings, bringing them up to the current state of knowledge. This will enable you to judge how well arguments have held up and realize the increasing gap between industry stagnation --  and scientific progress.

THEN: THE IMPORTANCE OF RELATIONAL TERMINOLOGY (t&n)

(email exchange with a reader originally published September 2002)

“Saw your latest and once again I think you have hit one of the many protruding nails on the head. Understanding one's data is so central and so crucial and yet so often ignored.

All this talk (not from you, I note) of silver bullets. Nothing new and I wonder if the paying customers and the big-ticket so-called technology strategy companies will ever wise up. Edward de Bono wrote of 'porridge words' that distract thought from the matter at hand. When used sparingly, they can facilitate new lines of thought but when, as they are in this field, they are used so casually and often they blur the real issues. All this technicalese of XML etcetera has this effect on me.

During one of the few times an employer allowed me to help people with logical design, I was having difficulty because the customer's IT staff knew very little English and had perhaps even less database background. I hit on the idea of explaining tables as relations and relations as sentences - sentences that must have the same 'size and shape'. Their faces seemed to light up and when they agreed that they had overloaded some of their tables, I was very pleased with myself. I felt vindicated a few weeks later when I read an article about predicates and propositions that Hugh Darwen had written in the now defunct DBPD magazine, put these thoughts much more precisely than I could, . Of course, the changes created new problems because the database product, like so many others, gave precious few ways to map the logical design to the physical one. But I regarded these as preferable problems since the staff was much more interested in the more concrete physical optimization techniques.

Without any disrespect to Dr. Codd (who I once met but was too awe-struck to ask any questions of), I have often thought that the language used by everybody in the field, with words such as "tables", nearly always brings connotations of physical arrangements to the mind of anybody who has done traditional programming. This seems unfortunate to me. Especially after I read Mr. McGoveran's proposals for results that might embody more than one table. (I wonder if these might not be part of the key for much better physical integration of databases with their visualization for users, not to mention smarter engines.)

I came across a site https://www.mcjones.org/System_R/ the other day, where a bunch of the System R people reminisced about its development on the occasion of, I think, the 25th anniversary of one of Codd's early papers. Presumably Mr. Date was absent from this gathering so that he could write his own most interesting history, which I remember reading five or six years ago. Anyway, I was struck again by how often their design decisions were either determined or distorted by physical considerations. And now, when many of the obstacles have been overcome courtesy of Moore's and other laws, some of those clever people seem regretful.

Also, please let me submit an historical, non-technical 'nit' to Mr. Date - I remember him writing that Codd did not coin the database term 'normalization of relations' as a result of R.M. Nixon's foreign policy excursion with China. But I also remember reading what I recall was an original interview with Dr. Codd in the DBMS magazine where he stated that this was the case. It's not really important, perhaps I'm just sensitive to it because I live in a country that established relations with modern China a year earlier!”