What is an instance in the ER diagram

Entity relationship diagram

entityAn entity is the set of similar entities in the business world to be modeled. The term entity set would be more precise, but the term instance is used for a specific entity in this set. viewA view summarizes the attributes of one or more entities in a table. The lines of a view can contain redundant data. The term attribute set is used as a generic term for entity and view. Combined view
Union view

A view can be modeled by sub-views, which are combined with UNION, UNION ALL, INTERSECT or EXCEPT and brackets.

Select statement
Sub-Select like View

As a select statement, a select is part of a union view or is used as a sub-select in expressions of view elements.

attributeThe attributes of an entity describe the characteristics of an instance. Primary keyA key is a subset of the attributes of its entity that can be used to uniquely identify an instance. If the values ​​of the key attributes remain absolutely unchanged over the entire lifetime of their instance, it is a so-called key candidate. From the set of key candidates, the primary key that is best suited for the implementation of a relationship through a foreign key is selected. If an entity in the real world does not have a key candidate, an artificial key is usually defined that contains a number attribute specially modeled for it.Alternative keyView attributeThe values ​​of view attributes are determined from the values ​​of the attributes used. Calculation expressions with functions can also be used.Value testA value check restricts the possible values ​​of attributes. It is the counterpart to an SQL check constraint from the DB model.R typeTechnically speaking, an R-Type is a relationship. These entities are required to ensure the 1st normal form in a model that is to be mapped on a relational database. Classically, these are many-to-many relationships.Extensions for multidimensional modeling:Dimension entity

In a complete model there is an orthogonal ring with respect to the cube, its cube dimensions, and fact sets.

This means that the dimension of a cube dimension has a lowest dimension level that is linked to a dimension entity of the entity relationship model. This dimension entity is in turn referenced in a fact set using a foreign key relationship. And this set of facts is used by the cube via a from clause, so that the cube gets its key figures from the set of facts. The foreign attributes of the fact set are displayed in the cube as dimension attributes.

Fact entityDimensionsviewFact viewExtensions for Data Vault:Hub entityA hub entity describes a core object of the business logic (e.g. product), which is usually very stable, which contributes to the longevity of the data model.Link EntityA link entity represents the relationships between the business objects, e.g. between customer and product.Satellite entityAll information describing the hub entity or the link entity is stored in the satellite entity.Extensions for NoSQL:NoSQL schemeUsed to integrate unstructured NoSQL data.NoSQL GroupNoSQL attributes