Physical schema

In the lifecycle of a project it typically derives from a logical data model, though it may be reverse-engineered from a given database implementation.

As of 2012[update] seven main databases dominate the commercial marketplace: Informix, Oracle, Postgres, SQL Server, Sybase, IBM Db2 and MySQL.

Physical data models for each implementation would differ significantly, not least due to underlying operating-system requirements that may sit underneath them.

It's the same SQL Server database engine, with many similar features and services regardless of your operating system[2]), while Oracle and MySQL can run on Solaris, Linux and other UNIX-based operating-systems as well as on Windows.

Now logical schemas describe data in terms of relational tables and columns, object-oriented classes, and XML tags.