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