Monday, October 1, 2012

Part 4.4 Logical Data Modeling

Introduction to Logical Model

Logical Data Model refers to the actual implementation of a conceptual module in a database. It represents normalized design of common data model which is required to support the design of an information system.
The very core of the logical data model is the definition of the three types of data objects which the building blocks of the data model and these data objects are the entities, attributes, and relationships. Entities refer to persons, places, events or things which are of particular interest to the company.

Some examples of entities are Employees, States, Orders, and Time Sheets. Attributes refer to the properties of the entities. Examples of attributes for the Employee entity are first name, birthday, gender, address, age and many others. Lastly, relationships refer to the way where in the entities relate to each other.  An example relationship would be "customers purchase products" or "students enroll in classes". 

If the database is ported to another DBMS supporting a similar structure, the logical data model can still be used as a baseline for the new physical data model.

Characteristics of a Logical Model

  • Logical model works in an iterative manner.
  • Its design is independent of database.
  • It includes all entities and relationships among them.
  • All attributes for each entity are specified.
  • The primary key for each entity is specified.
  • Foreign keys (keys identifying the relationship between different entities) are specified.