1. Database Truth of the Week
"The original normal form and the later First Normal Form (1) are distinct. In the early 1969 RDM there was only "the normal form" of relations [a term Codd borrowed from FOPL]. It was based on the initial version of the join operation, which was different than today's join. Had 1NF and further normalization to at least 2NF had been introduced then, the normal form would have made no sense, as there would have been then multiple normal forms, which make sense only with the post-1970 join definition currently in use. Thus, there is no way to answer "what is the difference between the original normal form and 1NF?" without taking into account the definition of join, and -- if defined as we now do -- no way to understand the original normal form, except to say that in the context of the original join definition it would correspond to today's Fifth Normal Form (5NF). This is why a relation is really in 5NF by definition, not in 1NF as per current understanding." --David McGoveran
2. What's Wrong With This Database Picture?
"The term database design can be used to describe many different parts of the design of an overall database system. Principally, and most correctly, it can be thought of as the logical design of the base data structures used to store the data. In the relational model these are the tables and views. In an object database the entities and relationships map directly to object classes and named relationships. However, the term database design could also be used to apply to the overall process of designing, not just the base data structures, but also the forms and queries used as part of the overall database application within the database management system(DBMS).
The process of doing database design generally consists of a number of steps which will be carried out by the database designer. Usually, the designer must:
- Determine the data to be stored in the database.
- Determine the relationships between the different data elements.
- Superimpose a logical structure upon the data on the basis of these relationships.
Within the relational model the final step above can generally be broken down into two further steps, that of determining the grouping of information within the system, generally determining what are the basic objects about which information is being stored, and then determining the relationships between these groups of information, or objects." --Halil Lacevic, What is a Relational Database?, Quora.com
1. Database Truth of the Week
“A DBMS using the RDM for all its functionality would be very limited. The RDM only requires that the declarative data sub-language employed by users for data manipulation -- has power not more expressive than first order predicate logic (FOPL), which implies acceptance of certain limitations on what users can do directly in the language, in return for
Language declarativity and decidability;
Semantic correctness and system-guaranteed logical validity;
Physical and logical independence;Simplicity.”
--David McGoveran
2. What's Wrong With This Database Picture?
"The term database design can be used to describe many different parts of the design of an overall database system. Principally, and most correctly, it can be thought of as the logical design of the base data structures used to store the data. In the relational model these are the tables and views. In an object database the entities and relationships map directly to object classes and named relationships. However, the term database design could also be used to apply to the overall process of designing, not just the base data structures, but also the forms and queries used as part of the overall database application within the database management system(DBMS).
The process of doing database design generally consists of a number of steps which will be carried out by the database designer. Usually, the designer must:
- Determine the data to be stored in the database.
- Determine the relationships between the different data elements.
- Superimpose a logical structure upon the data on the basis of these relationships.
Within the relational model the final step above can generally be broken down into two further steps, that of determining the grouping of information within the system, generally determining what are the basic objects about which information is being stored, and then determining the relationships between these groups of information, or objects."
--Halil Lacevic, What is a Relational Database?, Quora.com
This post has been re-written as two posts:
1. Database Truth of the Week
“If the data sub-language ... has the power of second order predicate logic (SOPL), expressions are possible that cannot be evaluated (for example, self-referencing expressions) and the formal language is then undecidable, an algorithm to implement a declarative query language is impossible and all hope of physical independence is lost." --David McGoveran
2. What's Wrong With This Database Picture?
"Our terminology is broken beyond repair. [Let me] point out some problems with Date's use of terminology, specifically in two cases.
"type" = "domain": I fully understand why one might equate "type" and "domain", but ... in today's programming practice, "type" and "domain" are quite different. The word "type" is largely tied to system-level (or "physical"-level) definitions of data, while a "domain" is thought of as an abstract set of acceptable values.
"class" != "relvar": In simple terms, the word "class" applies to a collection of values allowed by a predicate, regardless of whether such a collection could actually exist. Every set has a corresponding class, although a class may have no corresponding set ... in mathematical logic, a "relation" is a "class" (and trivially also a "set"), which contributes to confusion.
In modern programming parlance "class" is generally distinguished from "type" only in that "type" refers to "primitive" (system-defined) data definitions while "class" refers to higher-level (user-defined) data definitions. This distinction is almost arbitrary, and in some contexts, "type" and "class" are actually synonymous."
I have recently -- yet again -- been accused in a LinkedIn exchange of "gibberish without any evidence" and of claiming that "nobody know what they're doing" with databases. I will leave it to readers to judge whether (1) five decades worth of writings and teaching is "no evidence" and (2) my comments in the exchange are gibberish. Here I would like to dare anybody to find claims to that effect in any of my pronouncements. What I did, do and will say is that most data professionals do not know and understand data and relational fundamentals -- an incontrovertible fact proved not just by me[1], but also by others[2,3] and that this inhibits real progress in database management.
As I wrote two weeks ago:
"The RDM put database management on a formal, scientific foot. Consequently, tool experience and relational terminology are insufficient -- foundation knowledge is necessary. Unfortunately, most data professionals do not possess it, in part because they have been misled by the industry and in part because few go through an education -- as distinct from training -- program that teaches the RDM and teaches it correctly. Consequently, even those with the heart in the right place defend the RDM without a full understanding, their views distorted by what passes for it (stay tuned for a debunking of such a recent example)."
I will now fulfill the promise by debunking just such a "heart-in-the-right-place" defense of the RDM.
1. Database Truth of the Week
“A network is a directed acyclic graph (the "direction" of the transitive relationship) and, thus, amenable to transitive closure (TC). In the Relational Data Model (RDM) that usually means the smallest set that includes all the members that satisfy the transitive relationship in question (for the count of each object type the closure is computed and the count ignores level). While the Relational Data Model (RDM) can handle an important subset of graph theory via special graph domain operators and extensions to the original relational operators, which could be made efficient, it is a very difficult problem. Certain computations on finite sets such as TC are not in general computable in a language based on first order predicate logic (FOPL) that is declarative, decidable and supports physical independence (PI) -- a core relational objective. They require a computationally complete language (CCL) that is imperative and recursive.
A ‘TC function’ can be implemented using a host CCL that returns its result in the form of a relation; then a symbol (i.e., pure syntax) of type relation can be defined in relational algebra that references/invokes that function. From within the algebra it appears to be just a relation and is up to the user to understand what the value of the returned relation means --i.e., that it represents the TC. That understanding/interpretation is outside the algebra and passed to users only via documentation (e.g., some meta-language).” --David McGoveran
2. What's Wrong With This Database Picture?
"I don’t like talking about the relational theory of data. It is absolutely fundamental to any deep understanding of data, but most practitioners get along fine without it. It’s more the implementers of database management systems (DBMSs) who need to understand relational theory, so teaching relational theory to ordinary practitioners is a bit like tormenting people with irrelevant theory before you let them get on with the business at hand. Moreover, some of those who understand relational theory use their knowledge to beat other people over the head with it. I don’t want to be associated with that high-handed approach to this important theory.
But I’ve been goaded. Google made me do it. My attention was drawn to a video put out by some folks at Google, Data Modeling for BigQuery. The video is fine for the most part, but it makes some misstatements about relational theory that just drive me crazy. They repeat commonly accepted misconceptions about relational databases—misconceptions that, unfortunately, have driven some of the “advances” we’ve seen of late in the realm of database technology. There have definitely been some true advances, but some new technology is merely different without being better.If you’re a practitioner, designing, implementing, and using databases, whether SQL or NoSQL, this won’t matter much to you, although it never hurts to learn a little more about the theory of data. However, if you are a programmer who might be the one who builds the next NoSQL mega-star that will replace decades-old technology, you need to know this, because this knowledge will enable you to blind-side every established DBMS vendor, whether SQL or NoSQL." --Ted Hills, Understand Relational to Understand the Secrets of Data
