Dimensional Model

A type of data modeling suited for data warehousing. In a dimensional model, there are two types of tables: dimensional tables and fact tables. Dimensional table records information on each dimension, and fact table records all the "fact", or measures.

1.                       Data modeling

There are three levels of data modeling. They are conceptual, logical, and physical. This section will explain the difference among the three, the order with which each one is created, and how to go from one level to the other.

2.                       Conceptual Data Model

Features of conceptual data model include:

• Includes the important entities and the relationships among them.
• No attribute is specified.
• No primary key is specified.

At this level, the data modeler attempts to identify the highest-level relationships among the different entities.

3.                       Logical Data Model

Features of logical data model include:

• Includes all entities and relationships among them.
• All attributes for each entity are specified.
• The primary key for each entity specified.
• Foreign keys (keys identifying the relationship between different entities) are specified.
• Normalization occurs at this level.

At this level, the data modeler attempts to describe the data in as much detail as possible, without regard to how they will be physically implemented in the database.

In data warehousing, it is common for the conceptual data model and the logical data model to be combined into a single step (deliverable).

The steps for designing the logical data model are as follows:

1.     Identify all entities.

2.     Specify primary keys for all entities.

3.     Find the relationships between different entities.

4.     Find all attributes for each entity.

5.     Resolve many-to-many relationships.

6.     Normalization.

4.                       Physical Data Model

Features of physical data model include:

• Specification all tables and columns.
• Foreign keys are used to identify relationships between tables.
• Demoralization may occur based on user requirements.
• Physical considerations may cause the physical data model to be quite different from the logical data model.

At this level, the data modeler will specify how the logical data model will be realized in the database schema.

The steps for physical data model design are as follows:

1.     Convert entities into tables.

2.     Convert relationships into foreign keys.

3.     Convert attributes into columns.

1.     http://www.learndatamodeling.com/dm_standard.htm

2.     Modeling is an efficient and effective way to represent the organization’s needs; It provides information in a graphical way to the members of an organization to understand and communicate the business rules and processes. Business Modeling and Data Modeling are the two important types of modeling.

The differences between a logical data model and physical data model is shown below.

Logical vs Physical Data Modeling

Logical Data Model	Physical Data Model
Represents business information and defines business rules	Represents the physical implementation of the model in a database.
Entity	Table
Attribute	Column
Primary Key	Primary Key Constraint
Alternate Key	Unique Constraint or Unique Index
Inversion Key Entry	Non Unique Index
Rule	Check Constraint, Default Value
Relationship	Foreign Key
Definition	Comment

Below is the simple data model

Below is the sq for  one of sq for the  dimension table load

 

 Logical Design

 Physical Design