What is the Codd rule and how does it relate to RDBMS?

Answer 1

Codd's Rule Maulin Thaker Ahmedabad There are 13 (0 to 12) rules which were presented by Dr. E.F.Codd ,in June 1970,in ACM (Association of Computer Machinery) Rule 0. Relational Database management “A relational database management system must use only its relational capabilities to manage the information stored in the database”. Rule 1. The information rule All information in the database to be represented in one and only one way, Namely by values in column positions within rows of tables. Rule 2. Logical accessibility This rule says about the requirement of primary keys. Every individual value in the database must be logically addressable by specifying the name of table, column and the primary key value of the row. Rule 3. Representation of null values The DBMS is required to support a representation of "missing information and inapplicable information" (for example, 0 'Zero' is different from other Numbers), This type of information must be represented by the DBMS in a systematic way (For example Null Character ). Rule 4. Catalog Facilities The system is required to support an on line, in line, relational data access to authorized users by using their Query language. Rule 5. Data Languages. The system must support a least one relational language (It may support more than one relational language) that (a) has a linear syntax, (b) can be used in two ways and within application programs, (c) supports data operations security and integrity constraints, and transaction management operations (commit). Rule 6. View Updatability All views that are theoretically updatable must be updatable by the system. Rule 7. update and delete. The system must support INSERT, UPDATE, and DELETE operators. Rule 8. Physical data independence Changes to the physical level (how the data is stored, whether in arrays or linked lists etc.) must not require a change to an application based on the structure. Rule 9. Logical data independence Changes made to tables to modify any data stored in the tables must not require changes to be made to application programs. Logical data independence is more difficult to achieve than physical data independence. Rule 10. Integrity Constraints Integrity constraints must be specified separately from application programs and stored in the catalog. It must be possible to change such constraints when they are unnecessarily affecting existing applications. Rule 11. Database Distribution The RDBMS may spread across more than one system and across several networks, however the tables should appear in same manner to every user like local users. Rule 12. The Non Subversion rule If the system provides a low-level interface, then that interface cannot be used to weaken the system (e.g.) bypassing a relational security or integrity constraint. One joking version of this is: "The Key, the whole Key, and nothing but the Key, so help me CODD". Which means that any piece of data should be reliant on only one primary key in a table. Search the web for database design or data normalization or CODD or all of it. Alternately, try searching for Boyce-Codd Normal Form, which is a specific form of normalization for relational databases.

Edgar F Codd (considered to be the pioneer of the Relational Database Management System (RDBMS) concept) proposed 12 Rules (one could perhaps consider them as key characteristics) to determine if an RDBMS is truly an RDBMS. From [1], and many other text-book sources (particularly those written by CJ Date): 1. Information Rule 2. Guaranteed Access Rule 3. Systematic Treatment of Null Values 4. Dynamic Online Catalog Based on the Relational Model 5. Comprehensive Data Sublanguage 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. Nonsubversion Rule Using these rules, there are actually very few systems which comes close to begin true RDBMSs