Editing Physical schema (section)

{{Short description|Representation of a data design}}
{{Refimprove|date=April 2008}}
[[File:Physical Data Model Options.jpg|thumb|320px|Physical data model options.<ref name="WH05">{{cite web |url=https://georgewbush-whitehouse.archives.gov/omb/egov/documents/CRM.PDF |title=FEA Consolidated Reference Model Document |date=May 2005 |page=91 |archive-url=https://web.archive.org/web/20100705040628/http://georgewbush-whitehouse.archives.gov/omb/egov/documents/CRM.PDF |via=[[NARA|National Archives]] |work=[[Office of Management and Budget]] |archive-date=July 5, 2010 }}</ref>]]

A '''physical data model''' (or '''[[database design]]''') is a representation of a data design as implemented, or intended to be implemented, in a [[database management system]]. In the [[Project lifecycle|lifecycle of a project]] it typically derives from a [[logical data model]], though it may be [[reverse-engineer]]ed from a given [[database]] implementation. A complete physical data model will include all the [[database artifact]]s required to create [[Relational database|relationships between tables]] or to achieve performance goals, such as [[index (database)|index]]es, constraint definitions, [[Associative entity|linking tables]], [[Partition (database)|partitioned tables]] or [[Data cluster|cluster]]s. Analysts can usually use a physical data model to calculate storage estimates; it may include specific storage allocation details for a given database system.

{{As of | 2012}} seven main databases dominate the commercial marketplace: [[Informix Dynamic Server|Informix]], [[Oracle Database|Oracle]], [[PostgreSQL|Postgres]], [[Microsoft SQL Server|SQL Server]], [[Sybase]], [[IBM Db2]] and [[MySQL]]. Other RDBMS systems tend either to be legacy databases or used within academia such as universities or further education colleges. Physical data models for each implementation would differ significantly, not least due to underlying [[operating system | operating-system]] requirements that may sit underneath them. For example: SQL Server runs only on [[Microsoft Windows]] operating-systems (Starting with SQL Server 2017, SQL Server runs on Linux. It's the same SQL Server database engine, with many similar features and services regardless of your operating system<ref>{{Cite web|url=https://docs.microsoft.com/en-us/sql/linux/sql-server-linux-overview|title=Overview of SQL Server on Linux - SQL Server|last=rothja|website=docs.microsoft.com|language=en-us|access-date=2019-04-28}}</ref>), while Oracle and MySQL can run on Solaris, Linux and other UNIX-based operating-systems as well as on Windows. This means that the disk requirements, security requirements and many other aspects of a physical data model will be influenced by the RDBMS that a [[database administrator]] (or an organization) chooses to use.