Entity Relationship Model in DBMS

Entity Relationship Model in DBMS

The conceptual simplicity of relational database technology triggered the demand for RDBMSs.

In turn, the rapidly increasing requirements for transaction and information created the need for more complex database implementation structures, thus creating the need for more effective database design tools.

Although the relational model was a vast improvement over the hierarchical and network models, it still lacked the features that would make it an effective database design tool.

Because it is easier to examine structures graphically than to describe them in a text, database designers prefer to use a graphical tool in which entities and their relationships are pictured.

Entity Relationship Model in DBMS

Thus, the entity relationship model in DMBS, or ER Model in DBMs, has become a widely accepted standard for data modeling.

ER models are normally represented in an entity relationship diagram (ERD) or ER diagrams in DBMS, which uses graphical representations to model database components.

The Components of Entity Relationship Model in DBMS:

Entity:

An entity was defined as anything about which data are to be collected and stored.

An entity is represented in the ERD by a rectangle, also known as an entity box.

The name of the entity, a noun, is written in the center of the rectangle.

The entity name is generally written in capital letters and is written in the singular form: PAINTER rather than PAINTERS, and EMPLOYEE rather than EMPLOYEES.

Relationships:

Relationships describe associations among data. Most relationships describe associations between two entities. when the basic data model components were introduced, three types of relationships among data were illustrated:

one-to-many (1:M),

many-to-many (M:N),

and one-to-one (1:1).

The ER model uses the term connectivity to label the relationship types.

The name of the relationship is usually an active or passive verb.

For example, a PAINTER paints many PAINTINGs; an EMPLOYEE learns many SKILLs; an EMPLOYEE manages a STORE.

The following figure the different types of relationships using two ER notations:

The original Chen notation and the more current Crow’s Foot notation.

The left side of the ER diagram shows the Chen notation, based on Peter chen’s landmark paper.

In this notation, the connectivities are written next to each entity box.

Relationships are represented by a diamond connected to the related entities through a relationship line.

The relationship name is written inside the diamond