Database Design and the E-R Model

      No Comments on Database Design and the E-R Model
Personal Development Category (English)728x90

Database Design

Database Design and the E-R Model

Design Phases for Database:

  • The initial phase of database design is to characterize fully the data needs of the prospective database users.
  • The designer chooses a data model
  • Fully developed conceptual schema also includes the functional requirements of the enterprise.

Points need to remember while design:

  • Redundancy
  • Incompleteness

An entity is a “thing” or “object” in the real world that is distinguishable from all other objects.

Did you know about Structure Query Language?

An entity has a set of properties and the values for some set of properties may uniquely identify an entity.

An entity set is a set of entities of the same type that share the same properties, or attributes.

For each attributes, there is a set of permitted values called the domain or value set of that attribute.

Types of Attributes:

  • Simple and composite attributes:
  • Single valued and multi valued.
  • Derived

Mapping Cardinalities: Mapping cardinalities or cardinality ratio express the number of entities to which another entity can be associated via relationship set. It must be one of the following:

  • One to One
  • One to Many
  • Many to One
  • Many to Many

Entity Relationship Diagram components:

  • Rectangles: represents entity sets
  • Ellipses: represents attributes
  • Diamonds: represents relationship sets
  • Lines: link attributes
  • Double ellipses: represents multi valued attributes
  • Dashed ellipses: derived attributes
  • Double lines: total participation of an entity in a relationship set.
  • Double rectangles: represents weak entity sets.

An entity set may not have sufficient attributes to form a primary key. Such an entity set is termed a weak entity set.

Leave a Reply