Databases 4

Chern ERD

A non-technical design method works on conceptual level based on the perception of real world.

• Consists of a collection of basic objects called entities and the relationship among the objects and attributes which define their properties.

Rectangles

Chen’s Format for ERDs: How are entities represented?

Lines with diamonds

Chen’s Format for ERDs: How are relationships represented?

Lines (with entities) with circles

Chen’s Format for ERDs: How are attributes represented?

Weak Entity, it is dependent on something else and cannot exist on its own

Chen’s Format for ERDs: When entities and relationships have an outline around them (double rectangle, double diamond), what does this mean?

Multivalued Attribute, a property of an entity that can hold more than one value (Example [phone_numbers]: Someone can have multiple phone numbers)

Chen’s Format for ERDs: What does it mean when the attribute has an outline around it (double attribute)?

Primary Key

Chen’s Format for ERDs: What does it look like if the text in an attribute is underlined?

Dotted outline

Chern’s Format for ERDs: What does it look like when an attribute (derived attribute) contains a value that can be determined using other attribute values?

Square, rounded

IE (Information Engineering) / Crow’s Foot Notation for ERDs: Strong entities are rectangles with ____ corners, weak entities exist with _____ corners

IE (Information Engineering) / Crow’s Foot Notation for ERDs:

IE (Information Engineering) / Crow’s Foot Notation for ERDs:

Top, divider line

IE (Information Engineering) / Crow’s Foot Notation for ERDs: Primary key attributes are listed in the ___ section of the rectangle, while everything else is separated by a ______ _____.

Non-ID Dependent Entity

Where each entity's primary key does not include the primary key of the other related entity; defined by a dotted line in IE notation

ID Dependent Entity

Where at least one entity’s primary key DOES include the primary key of the other related entity, defined by a solid line

Mission Objectives

Statements that represent the general tasks supported by the data maintained in the database; in which they help define tables, fields, relationships, and business rules that verify that database supports the Mission Statement

Mission Statement

Declares the specific purpose of the database in general terms:

• Defined at the beginning of the database design process

• Clarify purpose of the database project and provides a clearer path toward the efficient and effective creation of the required database system

Business RUles