Wissen > 1. Klassische Datenbanken > Persönlichkeiten > Edgar "Ted" Codd
Ted Codd wurde Mathematik an der Oxford Universität [1] unterrichtet; 1949 nahm er einen Job beim IBM Research Laboratory [2] in San Jose, Kalifornien, an.
1970 veröffentlichte er ein Papier mit dem Titel "A Relational Model of Data for Large Shared Data Banks", im Rahmen von Communications of the ACM (Volume 13 / Number 6 / June 1970) und veränderte die Entwicklung klassischer Datenbanken damit nachhaltig, sowohl im Bereich der relationalen Integrität, als auch funktionaler Abhängigkeit und Normalisierung.
Er entwickelte die erste relationale Abfragesprache namens ALPHA welche die Grundlage für die Entwicklung zur heute in Verwendung befindlichen Sprache SQL darstellt.
1985 veröffentlichte er 12 (eigentlich 13 inklusive einer Regel 0) Gesetze zum relationalen Datenbankmanagement.
Ted Codd veröffentlichte 1972 das sogenannte Codd Paper [3] und brachte so unbewusst eine Veränderung der Denkweise bezüglich Datenbank-Abfragesprachen und Datenbankkonzepte mit sich.
Die folgenden 12 Regeln wurden in seinem Buch "An Introduction to database Systems" (5. Auflage) auf Seite 389ff. dargelegt:
| 0. | (Yes, there is a Rule 0!) For a system to qualify as a RELATIONAL, DATABASE, MANAGEMENT system, that system must use its RELATIONAL facilities (exclusively) to MANAGE the DATABASE. |
| 1. | The information rule The information rule simply requires all information in the database to be represented in one and only one way, Namely by values in column positions within rows of tables. |
| 2. | The guaranteed access rule This rule is essentially a restatement of the fundamental requirement for primary keys. It says that every individual scalar value in the database must be logically addressable by specifying the mane of the containing table, the name of the containing column and the primary key value of the containing row. |
| 3. | Systematic treatment of null values The DBMS is required to support a representation of "missing information and inapplicable information" that is systematic, distinct from all regular values (for example, "distinct from zero or any other number," in the case of numeric values), and independent of data type. It is also implied that such representations must be manipulated by the DBMS in a systematic way. |
| 4. | Active online catalog based on the relational model The system is required to support an online, inline, relational catalog that is accessible to authorized users by means of their regular query language. |
| 5. | The comprehensive data sublanguage rule The system must support a least one relational language that (a) has a linear syntax, (b) can be used both interactively and within application programs, and (c) supports data definition operations (including view definitions), data manipulation operations (update as well as retrieval), security and integrity constraints, and transaction management operations (begin, commit, and rollback). |
| 6. | The view updating rule All views that are theoretically updatable must be updatable by the system. |
| 7. | High-level insert, update, and delete The system must support set-at-a-time INSERT, UPDATE, and DELETE operators. |
| 8. | Physical data independence Self-explanatory. |
| 9. | Logical data independence Self-explanatory |
| 10. | Integrity independence Integrity constraints must be specified separately from application programs and stored in the catalog. It must be possible to change such constraints as and when appropriate without unnecessarily affecting existing applications. |
| 11. | Distribution independence Existing applications should continue to operate successfully (a) when a distributed version of the DBMS is first introduced; (b) when existing distributed data is redistributed around the system. |
| 12. | The nonsubversion rule If the system provides a low-level (record-at-a-time) interface, then that interface cannot be used to subvert the system (e.g.) bypassing a relational security or integrity constraint. |