Thursday, June 10, 2021

Entities, Properties and Codd's Sleight of Hand

A recent LinkedIn post tried to illustrate in graphic form some old bunk that had been debunked to death decades ago: the purported inferiority of relational relative to directed graph database management. The plethora of "Great viewpoint!", "great representation", "love this!", "like", "Nice!, "Very clever!" reactions it triggered confirm the lack of foundation knowledge and familiarity with history of the field in the industry, without which there cannot be any progress. I will not waste any time debunking it. Instead, I will use a quote by a participant in the exchange from a Date and Darwen (D&D) book to bring up an important insight by David McGoveran.

“Overall, we believe the most appropriate design will emerge if careful consideration is given to the distinction between (a) declarative sentences in natural language, on the one hand, and (b) the vocabulary used in the construction of such sentences on the other. As we showed in Chapter 2 (but simplifying slightly here), it is unencapsulated tuples in relations that stand for those sentences, and it is encapsulated domain values in attributes in those tuples that stand for particular elements — typically nouns — in that vocabulary. To say it slightly differently (and to repeat what we said in Chapter 2, albeit in different words): Domains, or types, give us values that represent things we might wish to make statements about; relations give us ways of making those statements. Consider once again the EMP relvar of Design R. Suppose that relvar includes the tuple:


The existence of this tuple in the relvar means, by definition, that the database includes something that assert  that the following declarative sentence (statement) is true:

Employee E7, named Amy, is assigned to department D5 and earns a salary of $60,000."
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