AFM241 Study Guide - Midterm Guide: Unique Key, Functional Dependency, Database Design
30 May 2018
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E.g. A set of data describing a specific customer or product
Selecting and naming attributes
Attributes characteristics must be simple to ensure smooth operation and information extraction from
the database
A simple or atomic attribute is one that can be stated in a single component e.g., postal code
The opposite case is available in a composite attribute, where an attribute can be divided into more
meaningful components
E.g. employee name can be subdivided into first and last name
Generally, it is good practice to avoid composite attributes and use simple attributes
Attributes can also be categorized into single-valued and multivalued attributes
E.g. of single value = first name, last name, date of birth, SIN
E.g. of multivalued (one person may have more than one degree), phone number, email,
etc.
Generally, multivalued attributes are avoided in favor of single-valued ones
Transforming multivalued into single-valued attributes can be unfavourable in database design
sometimes
E.g. if you want to include more than one phone number for customers, we could add new
columns. But there will be unnecessary null values for customers who only have one
number
5.3.2 Associations
Associations exist among attributions of an entity and among entity occurrences
We say that there is a “one association from a set A to set B” if only one item in B can be associated with
an item in set A
E.g. we have set of biological mothers (A) and a second set with their children (B). A child
can have only one mother.
We say there is a “many association from A to B” if more than one item in B can be associated with a
given item in A
E.g. set A is a professor and set B are his students
Associations among attributes of an entity
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
A set of data describing a specific customer or product. Attributes characteristics must be simple to ensure smooth operation and information extraction from the database. A simple or atomic attribute is one that can be stated in a single component e. g. , postal code. The opposite case is available in a composite attribute, where an attribute can be divided into more meaningful components. E. g. employee name can be subdivided into first and last name. Generally, it is good practice to avoid composite attributes and use simple attributes. Attributes can also be categorized into single-valued and multivalued attributes. E. g. of single value = first name, last name, date of birth, sin. E. g. of multivalued (one person may have more than one degree), phone number, email, etc. Generally, multivalued attributes are avoided in favor of single-valued ones. Transforming multivalued into single-valued attributes can be unfavourable in database design sometimes.
