Tuesday, June 4, 2013

Compare Logical and Physical ERD

Entity relationship diagram (ERD) represents a detailed picture of the entities needed for a business. In forward engineering, ERD will be transformed into a relational database eventually. There are at least two types of ERD — Logical and Physical. They are used in different stages of development, and are inter-related.
Logical ERD models information gathered from business requirements. Entities and relationships modeled in such ERD are defined around the business's need. The need of satisfying the database design is not considered yet.
Physical ERD represents the actual design of database. It deals with conversion from logical design into a schema level design that will be transformed into relational database. When modeling a physical ERD, Logical ERD is treated as base, refinement occurs by defining primary keys, foreign keys and constraints. Sometimes, relationships need to be resolved by introducing additional tables, like a Linked table for a many to many relationship.
Since physical ERD and logical ERD represent the business requirement and database schema respectively, comparing physical and logical ERD helps to find out the differences between them, thus confirming the database is exactly following the initial business requirements regardless of the changes.

Visual Paradigm's Model Transitor enables you to transit a logical ERD to a physical ERD with the transition relationship well maintained. In this tutorial, we'll see how to make use of Model Transitor to transcribe a logical ERD into physical ERD. After that, we will make use of Visual Diff, a tool for comparing changes between diagrams, to trace the differences between them.

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