E-R図E-R Diagram

Learn in the textbookE-R Diagrams, Key Design, and Normalization

DefinitionAn E-R diagram (E-R図) shows the entities a business manages and the relationships between those entities.

ExplanationAn entity is a group of things you want to record as data, and a relationship shows how entities are connected. Each relationship is labeled with its multiplicity (one-to-one, one-to-many, many-to-many and so on), which tells how many records on one side match a single record on the other.

AnalogyThink of the character map for a TV drama. Each character gets a box, and lines labeled "parent" or "coworker" show at a glance who is connected to whom and how.

Memory hookE stands for Entity and R for Relationship, so the name itself lists the diagram's two building blocks.

Learn in the textbookBusiness Modeling and Business Improvement / Automation

DefinitionAn E-R diagram (E-R図) draws the things to be managed as entities and the links between them as relationships, showing the structure of data.

ExplanationEntities are drawn as rectangles and relationships as lines joining them (a diamond in some notations), and symbols at the line ends show counts such as one-to-many, called multiplicity. An item an entity holds, such as a student's name, is called an attribute. It is a typical data model for organizing the data a business handles, and it is the starting point for designing database tables.

AnalogyIt is like a chart that draws lines between a class roster and a course list to show who attends which course: it shows how things are linked, not the order in which events happen.

Memory hookE stands for Entity and R for Relationship.