Entity-Relationship A database or information system's structure can be modelled and described using a diagram. It aids in comprehending how data is arranged and the connections between various system elements. In order to plan and record database structures, ERDs are frequently used in database design and development.
Entities
The essential building elements of a database system's representation of actual things, ideas, or entities are known as entities in the context of database design. These things, which are frequently nouns, act as data storage and organisation units. A company database may contain the following entities: "Customer," "Product," "Employee," and "Order."
Attributes
The qualities or traits attached to entities are known as attributes, and they specify the types of data that may be stored by each object. An entity's attributes are used to specify the specific information that relates to it. For example, the "Customer" entity has attributes like "CustomerID," "FirstName," "LastName," and "Email." Similar to the fields or columns in a database table, attributes are a kind of data.
Cardinalities
The relationships between entities are described by cardinalities, which count the instances or records that are involved. The number of entities of one kind that are connected to entities of another type is specified by cardinalities. "1" (one instance), "0..1" (zero or one instance), "0..n" (zero to many instances), and "1..n" (one to many instances) are common cardinality notations Song (1995). Understanding the nature and restrictions of relationships inside a database schema requires knowledge of these cardinality constraints.
Relationships
Relationships in a database refer to the links or affiliations between two or more elements. They explain how entities relate to or interact with one another inside the framework of the database system. Relationships are frequently marked with labels that describe the type of affiliation, such as "Is a part of," "Works for," or "Has." Relationships are visually depicted by linking the relevant things with lines or symbols like diamonds. A well-structured database schema may be created with the aid of the relationships specified in an Entity-Relationship Diagram (ERD), which gives a clear understanding of the links between entities.
References:
Song, I.Y., Evans, M. and Park, E.K., (1995) A comparative
analysis of entity-relationship diagrams. Journal of Computer and Software
Engineering, 3(4), pp.427-459.
Comments
Post a Comment