Page 2 :
OVERVIEW OF CODD’s RULE, A relational database management system (RDBMS) is a, , database management system (DBMS) that is based on the, relational model as introduced by E. F. Codd., A short definition of an RDBMS may be a DBMS in which, data is stored in the form of tables and the relationship, among the data is also stored in the form of tables., E.F. Codd, the famous mathematician has introduced 12 rules, (0-12)for the relational model for databases commonly known, as Codd's rules. The rules mainly define what is required for a, DBMS for it to be considered relational, i.e., an RDBMS.
Page 3 :
This rule states that all subsequent rules are based on, , the notation that in order for a database to be, considered relational, it must use it’s relational, facilities exclusively to manage the database.
Page 4 :
, , , , , , , , , , All information in the database is to be, represented in one and only one way., All information in an RDB is represented as, values in the tables., This is achieved by values in column and rows of, tables., All information including table names, column, names and column data types should be available, in same table within the database., The basic requirement of the relational model.
Page 6 :
Rule 2: GUARANTEED ACCESS RULE, Each unique piece of data should be accessible by:table, , name+primary key(row) + attribute(column)., All data are uniquely identified and accessible via this, identity., Most RDBMS do not make the definition of the primary, key mandatory and are deficient to that extent .
Page 8 :
"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 DBMS for representing missing, information and inapplicable information in, a systematic way, independent of data type."
Page 9 :
NULLs may mean: Missing data, Not applicable, Should be handled consistently - Not Zero or Blank, Primary keys — Not NULL, Expressions on NULL should give NULL., Separate handling of missing and/or non applicable, , data., This is distinct to zero or empty strings
Page 11 :
, , , , , The data base 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., The authorized users can access the database, structure by using common language i.e. SQL, The structure description of the entire database, must be stored in an online catalog, known as, data dictionary, which can be accessed by, authorized users.
Page 12 :
A, , relational system may support several, languages and various modes of terminal, use. 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 the, following items :
Page 13 :
Data Definition (create, insert, update), View Definition, Data Manipulation (alter, delete, truncate), Integrity Constraints (primary key, foreign key, null, values), Authorization (GRANT , REVOKE), Transaction boundaries (begin, commit, rollback etc), , , Every RDBMS should provide a language to, allow the user to query the contents of the, RDBMS and also manipulate the contents of, the RDBMS.
Page 14 :
, , , , , , , , View = ”Virtual table”, temporarily derived, from base tables., Example: If a view is formed as join of 3, tables, changes to view should be reflected in, base tables., Not updatable: View does not have NOTNULL attribute of base table., All views that are theoretically updateable are, also updateable by the system.
Page 16 :
TO VIEW ONLY THE NAME AND MARKS OF THE STUDENT TABLE, WE CAN WRITE THE FOLLOWING SYNTAX:, CREATE VIEW RECORD, AS SELECT NAME, MARKS FROM STUDENT;, VIEW IS CREATED., SELECT * FROM RECORD;, name, , Marks, , SONALI, , 95, , TAMANNA, , 90, , RAJWINDER, , 90, , SAKSHI, , 86, , SADHANA, , 82
Page 17 :
This rule states that insert, update, and delete, operations should be supported for any retrievable, set rather than just for a single row in a single, table., It also perform the operation on multiple row, simultaneously ., There must be delete, updating and insertion at the, each level of operation. Set operation like union, all, union , insertion and minus should also supported., EXAMPLE:, Suppose if we need to change ID then it will reflect, everywhere automatically.,
Page 19 :
What is independence?, The ability to modify schema definition in on level without, affecting schema definition in the next higher level is called, data independence, , , The ability to change the logical (conceptual) schema without, changing the External schema (User View) is called logical, data independence., EXAMPLE:, The addition or removal of new entities, attributes, or, relationships to the conceptual schema should be possible, without having to change existing external schemas or having, to rewrite existing application programs.,
Page 21 :
, , , , The ability to change the physical schema without changing the, logical schema is called physical data independence., This is saying that users shouldn’t be concerned about how the, data is stored or how it’s accessed. In fact, users of the data, need only be able to get the basic definition of the data they, need., , EXAMPLE:, A change to the internal schema, such as using different file, organization or storage structures, storage devices, or indexing, strategy, should be possible without having to change the, conceptual or external schemas.,
Page 22 :
, , Data integrity refers to maintaining and assuring the, accuracy and consistency of data over its entire life cycle., , A minimum of the following two integrity constraints must, be supported:, 1., Entity integrity: No component of a primary key is, allowed to have a null value. That is, no records can have, NULL values in its Primary Key attribute., 2., , Relational integrity: For each distinct non-null foreign, key value in a relational database, there must exist a, matching primary key value from the same domain. In, other words, if a foreign key cannot have null values as, its component then it must refer a matching primary key, value with the same set of permitted values to accept, any new records.
Page 23 :
, , , , , , , , “THE RELATION DATA BASE MANAGEMENT HAS DISTRIBUTION, INDEPENDENCE”, Distribution independence implies that user should not have to be, aware of whether a database is distributed at different sites or not., Application program and adhoc request are not affected by the, change in distribution of physical data. Application program will, work even if the programs and data are moved on different site, The RDBMS may spread across the more one system or several, networks
Page 24 :
, , There should be no way to modify to database, structure other then through the multiple row data, base language(SQL)., , Example:, 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).”
Page 26 :
Question 1, What is true regarding NULL value requirements confirming to, Codd rule?, a. Null value should be zero., b. Null value should be space., c. Null value should represent missing information., d. Either a or b., Answer :, , , c. Null value should represent missing information., According to Codd rule, Null value should not be, any regular data like zero, spaces etc, but should, represent that data is not available.
Page 27 :
Question 2, According to Codd rule, how one should be able to access, information about data structures like databases, tables etc., a. Should be directly accessible via all programming, languages., b. Should be directly accessible via same query language, used for data manipulation (e.g. select, update statements, etc), c. Should be directly accessible via XML, d. All of the above, Answer :, b. Should be directly accessible via same query language, used for data manipulation. For example, SQL can be used, to retrieve information about the tables, the column types, etc.,
Page 28 :
Question 3, Which is true regarding multi row update?, , , a. Multiple row updates should be prohibited., b. Multiple row updates should be allowed only on, tables without null values., c. Multiple row updates should be possible., d. Multiple row updates should be allowed only on, integer data types, , Answer :, c. Multiple row updates should be possible.
