Relational Model and ER Model: in a Nutshell

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Relational Model and ER Model in a Nutshell

• P. Pete Chong

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Relational Model

• A Model based on relations
• A relation is a two-dimensional table
• Each row is called a tuple
• Each column is call an attribute

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Entity-Relationship Model

• Entity is a thing a collection (table) of
  attributes that are organized by relevance and
  usage.
• Relationship is how data are used together
• Three cardinalities 11, 1m, mn

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Create Well-Structured Tables Using ER Model

• Identify Entities and their Relationships and
  draw 1ERD
• Convert 1ERD to 2ERD
• 11 merge the tables
• 1m the primary key of 1 side becomes the
  foreign key on the m side
• mn create a third table that uses primary keys
  on both sides as composite key

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Create Well-Structured Tables Using
Normalization

• 1NF no repeating groups
• 2NF non-key attributes are functionally
  dependent on the primary key
• 3NF no transitive dependency
• DK/NF every constraint on the relation is a
  logical consequence of the definition of keys and
  domain

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Result

• All tables are in 3NF which eliminates most of
  the anomalies already
• Each table contains one theme