Sunday, July 16, 2017

Relations and Relationships Part II

This is a 6/21/17 rewrite of a 4/21/13 post, to bring it in line with McGoveran's interpretation of the real RDM envisioned by Codd. It is the second part of a debunking of a LinkedIn thread (the rewrite of the first part of which was posted two weeks ago).

The misconception that the RDM represents relationships of only one type--referential--most likely originates with the E/R conceptual modeling approach. It assumes an "absolute" distinction between entities (objects) and relationships. The distinction, however, is in the "eye of the modeler": objects, properties and object groups are all, in fact, relationships labeled differently as a matter of subjective, pragmatic convenience.  All those relationships expressed as business rules comprising a conceptual model are expressible in a relationally complete FOPL-based data language as integrity constraints enforcible by a RDBMS for consistency with the rules. That neither SQL, nor any other current data languages can express--nor can the DBMSs based on it enforce--all of them is the deficiency of their implementation, not a RDM weakness.  
Read it all.

Due to a glitch an earlier revision of an older post seems to have gotten lost. If you have not seen it, read it it here: To Really Understand Integrity, Don't Start with SQL.

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