Database Management Systems: Designing & Building Business Applications, 3/e
Gerald V. Post
ISBN: 0072919191 Copyright year: 2005
Unified Modeling Language
Entity-Relationship diagrams have traditionally been used to model database designs. However, they suffer from three major problems:
There is no standard. Several variations exist, and students trained in one diagramming technique have difficulty reading diagrams created with a different methodology.
ER diagrams tend to be messy and difficult to read.
The ER approach is weak at handling object-oriented design issues, such as inheritance (subtypes) and composition.
The UML class diagram resolves these problems by defining a standard diagram that handles all of the situations needed by database designers. Additionally, students are introduced to the foundations of object-oriented design.
The basic similarities between ER and class diagrams are:
Entities (classes) are drawn as boxes.
Binary relationships (associations) are drawn as connecting lines
N-ary associations (relationships) are drawn as diamonds.
The primary differences lie in the details:
Attributes are written in the class box.
Multiplicity of an association is shown as simple numerical notation instead of a cryptic icon.
Several association (relationship) types have predefined drawing methods.
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Sample UML Class diagram
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2005 McGraw-Hill Higher Education