RDBMS Concepts Session 1 Relational Database Model. To Learn or Teach Linux visit www.theskillpedia.com, A Marketplace for Learners and Trainers. Drawbacks of DBMS DBMS models are complex Difficult for new programmers and users. Therefore, training is required Costly system set up These drawbacks gave way for the new Relational Model Relational Model Dr. E. F. Codd described the Relation Model in 1970 He put 12 Rules describing the Relational Model All the RDBMS applications should follow the Rules Rules of Dr. E F codd. Rule (0): Foundation Rule Database must manage its data storage only using relational capabilities (table forms) Rule 1: Information Rule Database must represent its data as values of a table. Rule 2: Guaranteed Access Rule The data can be accessed by specifying the table name and the column name and the columns that defined the primary key . Primary key ensures that each value is unique and accessible. Rule 3: Systematic Treatment of NULL Values A null is a unknown value and every database must have a provision for storing NULL values. NULL != 0 NULL != space Rules of Dr. E F codd. (Contd.). Rule 4: Dynamic On-Line Catalog Based on the Relational Model User data in tables and the information about the table such as structure and other required information also in tables only. One as user tables and another as metadata this metadata is what called as system catalog. Rule 5: Comprehensive Sub Language There must be at least one language which supports data defining, view defining , manipulating data, integrity constraints. All the above should be supported with well defined syntax, as character strings. Rules of Dr. E F codd. (Contd.). Rule 6: View Updating Rule Should support a mechanism which designs different combinations of data from different tables called as views. All the view should be updateable. Views are virtual tables that contains extraction of data from the source tables Either it is a simple view or a complex view it should allow updates to the view. Rule 7: High Level Insert Update and Delete Rule Data manipulation operations treat Rows as a set. These set operations and relational operators are used to work on table. Use of insert, update and delete operations on views should act on their respective tables Rules of Dr. E F codd. (Contd.). Rule 8: Physical Data Independence Rule Changes in the data storage should not effect programs that access the data. Rule 9: Logical Data Independency Rule The data is stored in the files physically, but tables are logical structures. So for making any changes need in logical structures there is no need of any change in the application. Rule 10: Integrity Independency Rule Data integrity means the consistency and accuracy which keeps the garbage out of the database. Integrity constraints must be the supported functionality of any database application. Rules of Dr. E F codd. (Contd.). Rule 11: Distribution Rule To the end user all the commands should be working a same as it would working for the local database even though the database is in some other place and user is accessing through network. Rule 12: Non Subversion Rule All the constraints defined by the user using the SQL should not be by passed by any other way. Benefits of an RDBMS The ability to create multiple relations (tables) and enter data into them An interactive query language Retrieval of information stored in more than one table Provides a Catalog or Dictionary, which itself consists of tables (called system tables) Some Important Terms Relation : A table Tuple : A row in a table Attribute : A Column in a table Degree : Number of attributes Cardinality : Number of tuples Primary Key : A unique identifier for the table Domain : Pool of values from which specific attributes of specific relations draw their values Entity-Relationship Model E-R Modeling: Terminology Entity is anything that exists and is distinguishable Entity Set a group of similar entities Attribute properties that describe an entity Relationship an association between entities ER Modeling Notations ER Modeling: Entity ER Modeling: Types of Relationships E-R Model ER-Modeling: Key Constraint Key Constraints For Ternary Relationships E-R Modeling Participation Constraints E-R Modeling: Weak Entities Visit www.theskillpedia.com to teach or learn a skill For Any corporate Training Need, Call me at +91-9312406920

• published: 14 Jun 2015
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