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> As long as the iSeries maintains its object-
> based roots, the actual implementation of the
> database is moot.  Don't you agree?

no. "Relational" means something very specific
that has to do with the functionality and not with
the implementation. My problem with this is
that people say that the underlying (implementation)
database is relational when it is not. Here are Codd's
rules:

Criteria for Fully Relational

(Codd)  For any system that is advertised as, or claimed to be, a relational
database management system, that system must be able to manage data bases
entirely through its relational capabilities

·                  must support database insert, update, and delete multiple
records at-a-time (relation-at-a-time)

Codd's  12  Rules

1.              The Information Rule
2.              Guaranteed Access Rule
3.              Systematic Treatment of Null Values
4.              Dynamic On-line Catalog Based on the Relational Model
5.              Comprehensive Data Sub-language Rule
6.              View Updating Rule
7.              High-level Insert, Update, and Delete
8.              Physical Data Independence
9.              Logical Data Independence
10.       Integrity Independence
11.       Distribution Independence
12.       Non-subversion Rule

Codd's Rules 1 and 2

Codd Rule 1: The Information Rule

All information in a relational database is represented explicitly at the
logical level and in exactly one way - by values in tables

·                   including table names, column names, domain names
·                   including database administration data

 Codd Rule 2: Guaranteed Access Rule

Each and every datum (atomic value) in a relational database is guaranteed to
be logically accessible by resorting to a combination of table name, primary
key value, and column name

·                   must have a primary key
·                   associative addressing scheme

Codd's Rules 3 and 4

Codd Rule 3:  Systematic Treatment of Null Values

Null values (distinct from the empty character string or a string of blank
characters and distinct from zero or any other number) are supported in fully
relational database management systems for representing missing information
and inapplicable information in a systematic way, independent of data type

·                   "nulls not allowed" must be available
·                   not just a "special value", type independent
·                   need to support 3-valued logic

 Codd Rule 4:  Dynamic On-line Catalog Based on the Relational Model

The database description is represented at the logical level in the same way
as ordinary data, so that authorized users can apply the same relational
language to its interrogation as they apply to the regular data

·                   need only learn one model
·                   can patch vendor's design oversights

Codd's Rules 5 and 6

Codd Rule 5:  Comprehensive Data Sub-language Rule

A relational system may support several languages and various modes of
terminal use (for example, the fill-in-the-blanks mode).  However, there must
be at least one language whose statements are expressible, per some
well-defined syntax, as character strings and that is comprehensive in
supporting all of the following items:

·                   data definition
·                   view definition
·                   data manipulation
·                   integrity constraints
·                   authorization
·                   transaction boundaries

(should not need several languages)

Codd Rule 6:  View Updating Rule

All views that are theoretically updateable are also updateable by the system

·                   insertion, deletion, modification
·                   not required to invert arithmetic or functions

Codd's Rules 7 and 8

 Codd Rule 7:  High-level Insert, Update, and Delete

The capability of handling a base relation as a single operand applies not
only to the retrieval of data but also to the insertion, update, and deletion
of data

·                   permits performance enhancements
·                   non-navigational
·                   system free to cluster distributed transactions by site

 Codd Rule 8:  Physical Data Independence

Application programs and terminal activities remain logically unimpaired
whenever any changes are made in either storage representations or access
methods

·                   boundaries between logical and semantic aspects
·                   boundaries between physical and performance aspects

Codd's Rules 9 and 10

 Codd Rule 9:  Logical Data Independence

Application programs and terminal activities remain logically unimpaired when
information-preserving changes of any kind that theoretically permit
un-impairment are made to the base tables

Ex:  split table in 2 by row selection
Ex:  split table in 2 by columns, repeating key
Ex:  combine 2 tables by "lossless" join
·                   can "make mistakes" in design and fix it

Codd Rule 10:  Integrity Independence

Integrity constraints specific to a particular relational database must be
definable in the relational data sub-language and storable in the catalog,
not in the application programs

·                   entity integrity (no component of a primary key is
allowed to be null)
·                   referential integrity (non-null foreign key values must
have matching primary key values)
·                   additional integrity
·                   must be part of the database management system engine

Codd's Rules 11 and 12

Codd Rule 11:  Distribution Independence

A relational database management system has distribution independence

DBMS has a data sub-language with logically unimpaired application programs
and terminal activity under

·                   the first occurrence of data distribution
·                   data redistribution

Codd Rule 12:  Non-subversion Rule

If a relational system has a low-level (single-record-at-a-time) language,
that low level cannot be used to subvert or bypass the integrity rules and
constraints expressed in the higher-level relational language
(multiple-records-at-a-time)

·                   no bypass of integrity





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