•Information is everywhere in an organization
•Information is stored in databases
–Database – maintains information about
various types of objects (inventory), events (transactions), people
(employees), and places (warehouses)
•
Entities and Attributes
•Database models include:
–Hierarchical database model – information is organized into
a tree-like structure (using parent/child relationships) in such a way that it
cannot have too many relationships
–Network database model – a flexible way of representing
objects and their relationships
–Relational database model – stores information in the form
of logically related two-dimensional tables
•Entity – a person, place, thing, transaction, or
event about which information is stored
–The rows in each table contain the entities
–In Figure 7.1 CUSTOMER includes Dave’s Sub Shop and Pizza
Palace entities
–
•Attributes
(fields, columns) – characteristics or
properties of an entity class
–The columns in each table contain the attributes
–In Figure 7.1 attributes for CUSTOMER include Customer ID,
Customer Name, Contact Name
•Primary keys and foreign keys identify the
various entity classes (tables) in the database
–Primary key – a field (or group of fields)
that uniquely identifies a given entity in a table
–Foreign key – a primary key of one table
that appears an attribute in another table and acts to provide a logical
relationship among the two tables