Data Modeling

• Businesses assume the creation and manipulation of data.
• Data = corporte wide resource: transctional data, oricess data, external data.
• Data = value
• The types of data used within an organization does not change much.
• Data has certain inherent properties.
• If we structure data according to their inherent properties, the structure (i.e models will be stable)
• Data @ the core of database technologies.

ERD

entity-relationship diagram

• invented by Peter Chen 1976
  • A conceptual / logical data modeling tool
  • A user-oriented approach
  • A graphic-based method

Entity

An entitiy is an object / phenomenon, real or abstract about which we would like to store data.

An entity is described by a set of atributes How to select entities ? Information required by your buisness process. Things that are of interest to the business that need to be remembered in order or manage and track them.

Relationship

• A relationship type is an association between two entities.
• Relationship membership is the participation of an entity in a relationship.
• A relationship can involve only two entities.

Relationship cardinality

• One-to-One 1:1

Countries - Capital cities

• One-to-Many 1:M

Books - Pages

• Many-to-Many M:N

Authors - Books

Crow foot notation

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Legend:

A:

• A customer has 0 or more orders. (modeled next to the order)
• An order has at least and at most 1 customer (modeled next to the customer)

B:

• An order has least one or more line Items.
• a line item has at least and at most 1 order.

C:

• A delivery address has at least 1 or more customers. (two customers live at the same address)
• A customer has one or more addresses. (two different homes)

Many-To-Many Relationships - Junction table:

If you want to have a many to many relationship you need an extra table

For example: If you want to have a relationship between table 1 and table 2:

primary key	foreign key (table 1)	foreign key (table 2)
1	30	40

Notations:

• Crow's Foot
• Chen notation
• Bachman
• Min-Max
• UML