Editing Conceptual schema

{{Short description|High-level database design model}}
{{Refimprove|date=September 2014}}
A '''conceptual schema''' or '''conceptual data model''' is a high-level description of informational needs underlying the design of a [[database]].<ref>{{cite book |isbn=978-0-12-805476-5 |title=Topological UML Modeling: An Improved Approach for Domain Modeling and Software Development |last1=Osis |first1=Janis |last2=Donins |first2=Uldis |date=20 June 2017 |publisher=Elsevier Science }}</ref><ref>{{cite book |isbn=978-0-12-411461-6 |title=Business Intelligence Guidebook: From Data Integration to Analytics |last1=Sherman |first1=Rick |date=21 November 2014 |publisher=Elsevier Science }}</ref>  It typically includes only the core concepts and the main relationships among them. This is a high-level model with insufficient detail to build a complete, functional database.<ref>{{cite book |isbn=978-0-12-385126-0 |title=Data Architecture: From Zen to Reality |last1=Tupper |first1=Charles |date=2011 |publisher=Morgan Kaufmann }}</ref> It describes the structure of the whole database for a group of users. The conceptual model is also known as the [[data model]] that can be used to describe the conceptual schema when a database system is implemented.{{cn|date=March 2020}} It hides the internal details of physical storage and targets the description of entities, datatypes, relationships and constraints.

== Overview ==

A conceptual schema is a map of [[concept]]s and their [[Relational model|relationships]] used for [[database]]s.  This describes the [[semantics]] of an organization and represents a series of [[Logical assertion|assertion]]s about its nature.  Specifically, it describes the things of significance to an [[organization]] (''entity classes''), about which it is inclined to collect information, and their characteristics (''attributes'') and the associations between pairs of those things of significance (''relationships'').

Because a conceptual schema represents the semantics of an organization, and not a [[database design]], it may exist on various levels of abstraction.  The original [[ANSI]] four-schema architecture began with the set of ''external schemata'' that each represents one person's view of the world around him or her.  These are consolidated into a single ''conceptual schema'' that is the superset of all of those external views.  A data model can be as concrete as each person's perspective, but this tends to make it inflexible.  If that person's world changes, the model must change.  Conceptual data models take a more abstract perspective, identifying the fundamental things, of which the things an individual deals with are just examples.

The model does allow for what is called [[Inheritance (object-oriented programming)|inheritance]] in [[object oriented]] terms.  The set of [[Instantiation (computer science)|instance]]s of an entity class may be subdivided into entity classes in their own right.  Thus, each instance of a ''sub-type'' entity class is also an instance of the entity class's ''super-type''. Each instance of the super-type entity class, then is also an instance of one of the sub-type entity classes.

[[supertype|Super-type]]/[[Subtyping|sub-type]] relationships may be ''[[exclusive relationship (programming)|exclusive]]'' or not. A methodology may require that each instance of a super-type may ''only'' be an instance of ''one'' sub-type. Similarly, a super-type/sub-type relationship may be ''exhaustive'' or not. It is exhaustive if the methodology requires that each instance of a super-type ''must be'' an instance of a sub-type. A sub-type named "Other" is often necessary.

==Example relationships==
* Each PERSON may be ''the vendor in'' one or more ORDERS.
* Each ORDER must be ''from'' one and only one PERSON.
* PERSON is ''a sub-type of'' PARTY.  (Meaning that every instance of PERSON is also an instance of PARTY.)
* Each EMPLOYEE may have a ''supervisor'' who is also an EMPLOYEE.

== Data structure diagram ==
[[Image:Data Structure Diagram.jpg|thumb|right|Data structure diagram and a [[data dictionary]] ]]
A [[data structure diagram]] (DSD) is a data model or diagram used to describe conceptual data models by providing graphical notations which document entities and their relationships, and the constraints that bind them.

== See also ==
{{colbegin}}
* {{annotated link|Concept mapping}}
* {{annotated link|Conceptual framework}}
* {{annotated link|Conceptual graphs}}
* {{annotated link|Conceptual model (computer science)}}
* {{annotated link|Data modeling}}
* {{annotated link|Entity-relationship model}}
* {{annotated link|Object-relationship modelling}}
* {{annotated link|Object-role modeling}}
* {{annotated link|Knowledge representation}}
* {{annotated link|Logical data model}}
* {{annotated link|Mindmap}}
* {{annotated link|Ontology (computer science)|Ontology}}
* {{annotated link|Physical data model}}
* {{annotated link|Semantic Web}}
* {{annotated link|Three schema approach}}
{{colend}}

== References ==
{{reflist}}

== Further reading ==
* Perez, Sandra K., & Anthony K. Sarris, eds. (1995) Technical Report for IRDS Conceptual Schema, Part 1: Conceptual Schema for IRDS, Part 2: Modeling Language Analysis, X3/TR-14:1995, American National Standards Institute, New York, NY.
* [[Terry Halpin|Halpin T]], [[Tony Morgan (computer scientist)|Morgan T]] (2008) Information Modeling and Relational Databases, 2nd edn., San Francisco, CA: Morgan Kaufmann.

==External links==
* A different [http://www.agiledata.org/essays/dataModeling101.html point of view], as described by the [[Agile software development|agile]] community

{{Data model}}

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[[Category:Data modeling]]
[[Category:Conceptual modelling]]