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An entity–relationship model (or ER model) describes interrelated things of interest in a specific domain of knowledge. A basic ER model is composed of entity types (which classify the things of interest) and specifies relationships that can exist between entities (instances of those entity types).
For example, as soon as you want to find seasonal or geographical trends in the sales of the item, you need information from the related Order record. An order would not exist without a product and a person to create the order, so it could be argued that an order would be described as a weak entity and that products ordered would be a ...
In systems analysis, a one-to-many relationship is a type of cardinality that refers to the relationship between two entities (see also entity–relationship model). For example, take a car and an owner of the car. The car can only be owned by one owner at a time or not owned at all, and an owner could own zero, one, or multiple cars.
An associative entity is a term used in relational and entity–relationship theory. A relational database requires the implementation of a base relation (or base table) to resolve many-to-many relationships. A base relation representing this kind of entity is called, informally, an associative table. An associative entity (using Chen notation)
Overview of a data-modeling context: Data model is based on Data, Data relationship, Data semantic and Data constraint. A data model provides the details of information to be stored, and is of primary use when the final product is the generation of computer software code for an application or the preparation of a functional specification to aid a computer software make-or-buy decision.
Example of supply chain Some additional descriptions for the supply chain. SCOR improves on this by offering a "standard" solution. The first step is to recover the Level 1 and Level 2 process descriptions. Caption from SCOR 8.0 Completed mappings of the supply chain processes with SCOR SCOR thread diagram. The example is of a simple supply chain.
In this example, the three lines next to the song entity indicate that an artist can have many songs. The two vertical lines next to the artist entity indicate songs can only have one performer. In the real world, data modeling is critical because as the data grows voluminous, tables linked by keys must be used to speed up programmed retrieval ...
Instead, the C4 model recommends using simple diagrams based on nested boxes in order to facilitate interactive collaborative drawing. The technique also promotes good modelling practices such as providing a title and legend on every diagram, and clear unambiguous labelling in order to facilitate the understanding by the intended audience.