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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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