Paper Topic:

ERD - Entity Relationship Diagram

Entity Relationship Diagram (Student Name

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Entity Relationship Diagram

Databases are used to store structured data that are stored in tables The structure of this data , together with other constraints , can be designed using a variety of techniques . One of which is called as entity-relationship modeling (ERM . The basic object that the entity-relationship model represents is an entity , which is a thing in the real world with an independent existence (such as person , car house , etc ) or it may be an object with a conceptual

existence (such as company , job , courses , etc .Entity is represented as table in database Each entity has attribute that describes it (name , age , address , etc (Elmasri Navathe 2002 . Diagram made for ERM . Process is an entity relationship diagram (ERD

Figure 1 : Entity Relationship Diagram (ERD

Source : Powell (2006 , Beginning Database Design

An ERD is a type of conceptual data model or semantic data model . Tables (entity ) can have various types of relationships between them . The different types of inter-table relationships that can be formed between different tables can be best described as displayed in Entity Relationship Diagrams (ERDs . An ERD displays tables and relationships between those tables . Figure 1 shows an example ERD for tables in a schema containing published books . A table is often referred to as an entity in an ERD (Powell 2006

Multiplicity is the type of relationship that exists between entities in database . There are three types of multiplicities (relationship one-to-one , one-to-many and many-to-many and they are described in details in below paragraphs

One-to-one relationships are often created to remove frequently NULL valued fields from a table (Powell 2006 . This type of relationship rarely exists in any database model . In figure 2 (a ) one-to-one relationship is shown between Rank entity and Edition entity . Here this relationship implies that there is exactly one row in the rank entity for every row in Edition entity

Figure 2 : Relationship (a ) One-to-one (b ) One-to-many

Source : Powell (2006 , Beginning Database Design

One-to-many relationships are extremely common in the relational database model between tables (Powell 2006 . In figure 2 (b ) one-to-many relationship is shown between Author entity and Publication entity . Here this relationship implies that there can be many published work for each author

Figure 3 : Relationship (c ) Many-to-many

Source : Powell (2006 , Beginning Database Design

A many-to-many relationship means that for every one record in one table there are many possible records in another related table , and visa versa for both tables (Powell 2006 . In figure 3 (c ) Many-to-many relationship is shown between Publisher entity and Publication entity . Here this relationship implies that a publisher can publish many books and a single book can be published by many publishers , when assuming multiple editions of a single book . One another example of this type of relationship is many students enrolled in many courses at a university Student can take many courses and similarly course has many students enrolled result in a many-to-many relationship between students and courses

References

Powell Gavin . Beginning Database Design . Indianapolis...

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