Database Reference
In-Depth Information
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A relationship is an inherent mapping involving two or more
relations. There are six types of relationships: one-to-one (1:1)
relationship, one-to-many (1:M) relationship, many-to-one (M:1)
relationship, many-to-many (M:M) relationship, component
relationship, and subtype relationship.
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An E-R diagram (ERD) is a graphical representation of a database
model. It is important to know how to represent relations/entities
and relationships on the ERD.
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It is important to know how to implement the various types of
relationships in the actual database design.
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The relation-attributes list (RAL) and relationship list (RL) are
two useful alternatives to the E-R diagram, especially for large,
complex systems.
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Database approaches that preexisted the relational approach
include the inverted-list approach, the hierarchical approach and
the network approach.
A contemporary alternative to the relational approach is the
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object-oriented approach. However, given the efficacy of both
approaches, it is more likely that they will complement each other
in the future, rather than compete against each other.
Take the time to go over this chapter more than once if you need to, and make
sure that you are comfortable with the concepts covered. In the upcoming chapter, we
will build on the information covered in this chapter, as we discuss integrity rules and
normalization. These two topics form the foundation for the rest of the course.
3.9 Review Questions
1.
Clarify the following terms:
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Entity
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Attributes
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Entity set
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Relation
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Relationship
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Tuples
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Primary key
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Candidate key
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Foreign key
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Domain
