Saturday, May 11, 2024

L/C: TABLES, DIMENSIONS & RDM



 

Note: I am working on entirely new papers (not re-writes) in the PRACTICAL DATABASE FOUNDATIONS series. Two were already published:

THE FIRST NORMAL FORM - A DEFINITIVE GUIDE
PRIMARY KEYS - A NEW UNDERSTANDING

and are available for ordering from the PAPERS page.

One is in progress:

RELATIONAL DATABASE DOMAINS: A DEFINITIVE GUIDE

and two are forthcoming:

DATABASE RELATIONS: A DEFINITIVE GUIDE
THE FINAL NULL IN THE COFFIN - A RELATIONAL SOLUTION TO MISSING DATA

will be forthcoming.

In the process I come across matters that, while not includable the papers, are worthy of setting straight in brief posts here. Here is another:

“Data is stored in two-dimensional tables consisting of columns (fields) and rows (records). Multi-dimensional data is represented by a system of relationships among two-dimensional tables.” 

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The tabular presentation format should not be confused with relational database structure and the dimensionality thereof -- it plays no role in RDM.

Database relations represent groups of entities that share a set of defining properties and are, thus, of the same type. Entities are represented by tuples, properties are represented by attributes in the database. Relations can be presented as tables on a physical medium: tuples appear as rows and attributes as columns, but the tabular arrangement on the medium plays no role in RDM. 

Attributes and tuples are logical, fields and records are physical.

It is the medium and, thus, the presentation of the relation on it that are two-dimensional. A relation is a relationship of domains and has as many dimensions as its cardinality (i.e., the number of attributes), and therefore is  multidimensional.

At the logical level relationships between relations (not tables!) are also represented by (associative) relations that are, therefore, also multidimensional.

 

 

 

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