Transforming Model Objects from Logical to Physical
Go Up to Developing the Physical Model
Before considering physical design issues, it is important to understand how a physical design maps to its corresponding logical design. When ER/Studio Data Architect derives a physical design from a logical one, it transforms logical model objects into their physical model analogs. The table below details how different logical objects are transformed into physical objects. Understanding the transformation lets you better assess the impact of altering the physical design to differ from the logical design.
The table below describes logical model objects and their corresponding physical model objects:
|
Logical Model Object |
Physical Model Object |
Notes |
|---|---|---|
|
Entity |
Table |
An entity translates directly into a table. In a dimensional model, tables are automatically assigned types (fact, dimension, snowflake, or undefined) based on an analysis of the schema. |
|
Attribute |
Column |
An attribute translates directly into a table column. |
|
View |
View |
Views translate directly between logical and physical models. However, some database platforms offer additional properties that can be applied to physical view definitions. |
|
Relationship |
Foreign Key |
A relationship becomes a foreign key in the physical design. You can enforce referential integrity through foreign key constraints or through triggers. |
|
Primary Key |
Unique Index or Primary Key Constraint |
You can enforce primary keys with unique indexes or primary key constraints, depending on the database platform. |
|
Alternate Key |
Unique Index or Unique Constraint |
You can enforce alternate keys with unique indexes or unique constraints, depending on the database platform. |
|
Inversion Entry Key |
Non-unique Index |
You can convert inversion entries into non-unique indexes. |
|
Default |
Default or Declared Default |
Data Dictionary defaults are converted to default objects for Sybase and Microsoft SQL Server. Otherwise, they are converted to declared defaults, if supported by the selected database platform. |
|
Rule |
Rule, Check Constraint, Default Value |
Data Dictionary rules are converted to rule objects for Sybase and Microsoft SQL Server. Otherwise, they are converted to check constraints, if supported by the selected database platform. |
|
Relationship |
Foreign Key |
|
|
Definition |
Comment |
|
|
User Datatype |
User Datatype or Base Datatype |
Data Dictionary datatypes are converted to user datatypes for Sybase and Microsoft SQL Server. Otherwise, they are converted into their underlying base datatype definitions. |
|
Domain |
Column Definition |
Domains are translated into the base column definition for each column that refers to a domain. |