Question

In 300 words or more, describe the advantages and concepts of a Chen ER diagram and how the diagram will help shape the overall relationship between tables.

Answer 1

Hi,

What is Chen's ERD?

The basic Chen diagram is the original entity relationship diagram that was developed by Peter Chen in 1976. The diagram is a graphical representation of entities and their relationships to each other.

Here Entity means a person, things, events , place or role for which you want to store data in table.

Relationship means the relation b/w the two entity exists. Like teacher and students, shop and customers etc.

Cardinality , which is most important part of ER diagram and it refers number of instances of one entity that can be related to an instance of another entity. like Cardinality is one to many or many to many.

Below image is showing notation(symbols) of Chen's ERD:

Image: Chen's ERD Notations

ERD graphical representations are used to embody database components. Included in these diagrams are entities, attributes, relationships, and cardinalities which are most important parts of any database. Every entity is described by attributes that identify characteristics of the entity.

In Chen's ERD notations ,

Entities are represented by rectangles with the entity name written inside.

Weak Entity , double rectangle The existence of a weak entity is dependent upon another entity called the owner entity. The weak entity’s identifier is a combination of the identifier of the owner entity and the partial key of the weak entity.

Associative entity, represent by diamond sign inside rectangle. An entity used in a many-to-many relationship (represents an extra table). All relationships for the associative entity should be many

Relationships are represented by a triangle;

Two entities can be connected with a line between them and their respective cardinalities written were the line connects each entity. An example of entities and relationships in written form is “one library hold many books.” In this instance, many books can only be hold by one library.

There are two types of relation exist in Chen ERD.

Strong relationship – a relationship where entity is existence-independent of other entities and PK of Child doesn’t contain PK component of Parent Entity. A strong relationship is represented by a single rhombus.

Weak relationship – a relationship where Child entity is existence-dependent on parent, and PK of Child Entity contains PK component of Parent Entity. This relationship is represented by a double rhombus:

Mandatory Relationship, is represented by solid line.

An optional relationship is represented by a dashed line.

Attributes, each attribute represented by oval symbol in chen notation and they are linked with entity by a straight lines.

Key attribute – an attribute that uniquely identifies a particular entity. underline attribute with line.

partial key attribute, an attribute that, when combined with the key attribute of the owner entity, provides a unique identification for the weak entity. We underline the discriminator with a dashed line:

Multivalued attribute ,an attribute that can have many values (there are many distinct values entered for it in the same column of the table). Multivalued attribute is depicted by a dual oval.

Derived attribute ,an attribute whose value is calculated (derived) from other attributes. The derived attribute may or may not be physically stored in the database. Its represented by single dashed oval.

Cardinality relationship:

one-to-one, one-to-many , many-to-one , many-to-many

There are many ERD which are derived from Chen notation like Crows Foot notation is derived from Chen notation. It is very similar to Chen notation and the only real differences are in the way that relationships are represented by symbols instead of letter or numbers. But except this , they are same.

Chen entity-relationship diagram (ERD) is crucial to creating a good database design. It is used as a high-level logical data model, which is useful in developing a conceptual design for databases. An entity is a real-world item or concept that exists on its own and many ERD are derived from Chen ERC.

Why Chen ERD:

• ER model allows you to draw Database Design
• It is an easy to use graphical tool for modeling data
• Widely used in Database Design
• It is a GUI representation of the logical structure of a Database
• It helps you to identifies the entities which exist in a system and the relationships between those entities

How the diagram will help shape the overall relationship between tables.

-It helps you to define terms related to entity relationship b/w two models.

-Define how two tables should be related with each other.

-What would be the fields/attributes in tables

-ERD describe entities, attribute and relationshiop b/w two tables.

Thanks

-