Editing Data model (section)

=== Data structure diagram ===
{{Main|Data structure diagram}}
[[File:Aggregate Data Structure Diagram.jpg|thumb|240px|Example of a Data Structure Diagram]]
A data structure diagram (DSD) is a [[diagram]] and data model used to describe [[Conceptual schema|conceptual data models]] by providing graphical notations which document [[entity class|entities]] and their [[Relational model|relationship]]s, and the [[Integrity constraints|constraint]]s that bind them. The basic graphic elements of DSDs are [[box]]es, representing entities, and [[arrow]]s, representing relationships. Data structure diagrams are most useful for documenting complex data entities.

Data structure diagrams are an extension of the [[entity–relationship model]] (ER model). In DSDs, [[Attribute (computing)|attribute]]s are specified inside the entity boxes rather than outside of them, while relationships are drawn as boxes composed of attributes which specify the constraints that bind entities together.  DSDs differ from the ER model in that the ER model focuses on the relationships between different entities, whereas DSDs focus on the relationships of the elements within an entity and enable users to fully see the links and relationships between each entity.

There are several styles for representing data structure diagrams, with the notable difference in the manner of defining [[Cardinality (data modeling)|cardinality]]. The choices are between arrow heads, inverted arrow heads ([[Entity–relationship model|crow's feet]]), or numerical representation of the cardinality.
[[File:B 5 1 IDEF1X Diagram.jpg|thumb|240px|left|Example of an [[IDEF1X]] entity–relationship diagrams used to model IDEF1X itself<ref name="FIPS184">[http://www.itl.nist.gov/fipspubs/idef1x.doc FIPS Publication 184] {{Webarchive|url=https://web.archive.org/web/20131203223034/http://www.itl.nist.gov/fipspubs/idef1x.doc |date=2013-12-03 }} released of IDEF1X by the Computer Systems Laboratory of the National Institute of Standards and Technology (NIST). 21 December 1993 (withdrawn in 2008).</ref>]]