Review of Attributes of the Relational Data Model

Review of Attributes of the Relational Data Model.

• The relational model is credited to E. F. Codd (1970) who was working at IBM
• Basic Definitions:
• Data Structure:  Data are organized into tables (often called relations, not to be confused withrelationships) with rows and columns.
• Data Manipulation:  The structured query language (SQL) is used to manipulate data in the tables.
• Data Integrity:  The DBMS has facilities to enforce business rules to maintain data integrity, e.g., not to delete a CUSTOMER row when there is a corresponding outstanding row in the CUSTOMER_ORDERStable.
• Relational Data Structure:
• A table is a two-dimensional representation of data.
• Each column is named and represents a field..
• A table can have any number of rows (within physical storage limitations).
• Each row is a record.
• We could delete all of the rows and the table would still exist.
• The shorthand notation to express the structure of a table is:

TABLE_NAME( PrimaryKeyField1, Field2, Field3, ... )

example: 
EMPLOYEE( EmpID, EmpName, Department, DateHired )

Note that the "..." simply means there could be additional fields. 
 

• Relational Keys:
• Primary Key: column (or combination of columns) that uniquely identifies a row.  We underline the primary key.
• Composite Key: a primary key that includes more than one column.
• Foreign Key: a field that links one table to another table.  A table can have an unlimited number of foreign keys linking to other tables.  We use a dashed underline for foreign keys.
• Properties of Tables (Relations):
• Each table in a database has a unique name.
• Each entry in a table at the intersection of a row/column can only store a single value (principle ofatomicity).  No multivalued fields are allowed in a table.
• Each row is unique.
• Each column has a unique field name.
• The sequence of rows as well as columns is insignificant and can be interchanged without changing the data.