Editing Database design (section)

== Conceptual data modeling ==
The first step of database design involves classifying data and identifying interrelationships. The theoretical representation of data is called an ''[[Ontology (information science)|ontology]]'' or a ''[[conceptual data model]]''.

=== Determining data to be stored ===
In a majority of cases, the person designing a database is a person with expertise in database design, rather than expertise in the domain from which the data to be stored is drawn e.g. financial information, biological information etc. Therefore, the data to be stored in a particular database must be determined in cooperation with a person who does have expertise in that domain, and who is aware of the meaning of the data to be stored within the system.

This process is one which is generally considered part of [[requirements analysis]], and requires skill on the part of the database designer to elicit the needed information from those with the [[domain knowledge]]. This is because those with the necessary domain knowledge often cannot clearly express the system requirements for the database as they are unaccustomed to thinking in terms of the discrete data elements which must be stored. Data to be stored can be determined by Requirement Specification.<ref>Teorey, T.; Lightstone, S. and Nadeau, T.(2005) ''Database Modeling & Design: Logical Design'', 4th edition, Morgan Kaufmann Press. {{ISBN|0-12-685352-5}}</ref>

=== Determining data relationships ===
Once a database designer is aware of the data which is to be stored within the database, they must then determine where dependency is within the data. Sometimes when data is changed you can be changing other data that is not visible. For example, in a list of names and addresses, assuming a situation where multiple people can have the same address, but one person cannot have more than one address, the address is dependent upon the name. When provided a name and the list the address can be uniquely determined; however, the inverse does not hold – when given an address and the list, a name cannot be uniquely determined because multiple people can reside at an address.  Because an address is determined by a name, an address is considered dependent on a name.

(NOTE: A common misconception is that the [[Relational models theory|relational model]] is so called because of the stating of relationships between data elements therein. This is not true. The relational model is so named because it is based upon the mathematical structures known as [[Relation (mathematics)|relations]].)

=== Conceptual schema ===
The information obtained can be formalized in a diagram or schema. At this stage, it is a [[conceptual schema]].

==== ER diagram (entity–relationship model) ====
[[Image:ER Diagram MMORPG.png|thumb|320px|A sample entity–relationship diagram]]

One of the most common types of conceptual schemas is the ER ([[entity–relationship model]]) diagrams.

Attributes in ER diagrams are usually modeled as an oval with the name of the attribute, linked to the entity or relationship that contains the attribute.

ER models are commonly used in information system design; for example, they are used to describe information requirements and / or the types of information to be stored in the database during the conceptual structure design phase.<ref>{{Cite journal |last1=Javed |first1=Muhammad |last2=Lin |first2=Yuqing |date=2018 |title=Iterative Process for Generating ER Diagram from Unrestricted Requirements |journal=Proceedings of the 13th International Conference on Evaluation of Novel Approaches to Software Engineering |publisher=SCITEPRESS – Science and Technology Publications |pages=192–204 |doi=10.5220/0006778701920204 |isbn=978-989-758-300-1 |doi-access=free}}</ref>