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Understanding Entity Relationship Diagrams: Symbols and Relationships Explained

An Entity Relationship Diagram (ERD) is a visual representation used to illustrate the relationships between entities in a database. ERDs utilize specific symbols: boxes represent entities, diamonds depict relationships, and ovals indicate attributes. There are three primary types of relationships: one-to-one, where each record in a table corresponds to exactly one record in another; one-to-many, where one record links to multiple records; and many-to-many, where multiple records relate to multiple counterparts. These diagrams are essential for effective database design and management.

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Understanding Entity Relationship Diagrams: Symbols and Relationships Explained

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  1. What is an Entity Relationship Diagram?

  2. An Entity Relationship Diagram is a graphic that is speacialized to illustrate or give examples of the inter –relationships between entities in a database.

  3. What are the symbols used in Entity Relationship Diagrams?

  4. Entity relationship diagrams often use symbols to represent three different types of information • Boxes –are commonly used to represent entities. • Diamonds-are normally used to represent relationships. • Ovals-are used to represent attributes.

  5. What is one-one relationship?

  6. One-one relationship occurs when there is exactly one record in the first table

  7. Example of One-one relationship

  8. If a database table contains a few columns of data that is frequently used and the remaining columns being infrequently used, the database designer may split the single table into 2 tables linked through a one-to-one relationship. Such a design would reduce the overhead needed to retrieve the infrequently used columns whenever  query is performed on the contents of the database table.

  9. What is One-many Relationship?

  10. One –many Relationships occurs when each record in a table labelled “A” have many linked records in a table labelled “B” which has only one corresponding recording in Table A

  11. Example of One-many Relationship

  12. All the customers belonging to a business is stored in a customer table while all the customer invoices are stored in an invoice table. Each customer can have many invoices but each invoice can only be generated for a single customer.

  13. What is Many-many Relationship?

  14. Many-many relationship is when one record in either table can relate to many records in the other table .

  15. Example of Many-many relationship

  16. All the customers belonging to a bank is stored in a customer table while all the bank's products are stored in a product table. Each customer can have many products and each product can be assigned to many customers.

  17. Name: Melisa LangleyForm:6BQ

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