Data Design The futureERD - CardinalityCODINGRelationshipsDefinition

ENTITY: An entity is a person, place, thing, or event for which data is collected and maintained. TABLE: contains a set of related records that store data about a specific entity FIELD: also called an attribute, is a single characteristic or fact about an entity RECORD: is a set of related fields that describes one instance, or occurrence, of an entity, such as one customer, one order, or one product

Database for Websites……..

Storage

Primary and Foreign Key Primary Key: is a field or combination of fields that uniquely and minimally identifies a particular member of an entity Foreign Key: is a field in one table that must match a primary key value in another table in order to establish the relationship between the two tables

One-to-one relationship, abbreviated 1:1, exists when exactly one of the second entity occurs for each instance of the first entity One-to-many relationship, abbreviated 1:M, exists when one occurrence of the first entity can relate to many instances of the second entity, but each instance of the second entity can associate with only one instance of the first entity Many-to-many relationship, abbreviated M:N, exists when one instance of the first entity can relate to many instances of the second entity, and one instance of the second entity can relate to many instances of the first entity Relationship

Easy Example

Create table PERSON ( SSN char(9), First_Name varchar(16), Last_Name varchar(16), …….. PRIMARY KEY (SSN)); Create table HOUSE ( HOUSE_ID int(15), ZIP char(5), ADDRESS1 varchar(25), …….. PRIMARY KEY (HOUSE_ID)); Create table OWN ( SSN char(9), HOUSE_ID int(15), DATE date, PRIMARY KEY (SSN, HOUSE_ID), FOREIGN KEY (SSN) references PERSON(SSN), FOREIGN KEY (HOUSE_ID) references HOUSE(HOUSE_ID));

A multidimensional database (MDB) is a type of database that is optimized for data warehouse and online analytical processing (OLAP) applications. Multidimensional databases are frequently created using input from existing relational databases The present and the future