Course: Database Systems Week 4: Discussion 1 Discussion 1 (Chapter 9): Discuss the correspondences between the ER model constructs and the relational model constructs. Show how each ER model construc
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Post 1:
Michael
RE: Anil_week 4 Discussion #1
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The entity relationship model is essential to database design as it outlines the general structure of the schema. How do each of the constructs within the ER model relate to the relational model though? Elmasri and Navathe (2017) connect each part of the ER model to the relational model as such:
Entity type – Entity-relationship
1:1 or 1:N relationship type - Foreign key
M:N relationship type – relationship relation and two foreign keys
N-ary relationship type – relationship relation and n foreign keys
Simple attribute – attribute
Composite attribute – set of simple component attributes
Multivalued attribute – Relation and foreign key
Value set – domain
Key attribute – Primary (or secondary) key
Each of the entity relationships and attributes are mapped to a specific attribute or key within the relational model. They also define a seven-step process for creating these relationships.
Reference
Elmasri, R., & Navathe, S. B. (2017). Fundamentals of database systems (7th ed.). Pearson.
Post 2:
Ricardo
Week 4 Dis # 1
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Hello,
For this week’s first discussion, we are asked to examine the differences between the ER model and the relational model. At first glance, the major differences are distinct. According to Taylor, the ER model specifically relates to entities and the relationships between the entities (Taylor, 2019). In contrast, the relational model deals with the tables, data, and relationships between the data. When we examine the ER model, the entities are clear, the relationships are highlighted, and the data attributes are detailed. When looking at the relational model, the structure of the tables, constraints for the columns, and data types are highlighted.
Taking a closer look at the two models, the ER diagram allows visual representation of entities and simply describes the high-level relationships between the entities. Research shows that the ER model is easier understood and gives a quick glance at the structure (Taylor, 2019). In contrast, the relational model is more difficult to determine the relationships between the tables in the database (Taylor, 2019). Moreover, research shows that the ER model shows data as an entity set, a relationship set, and attributes. The relational model describes data within the tables as domain, attributes, and tuples. It is important to understand that the ER model represents cardinality whereas the relational model does not take this constraint into consideration. If we were to map the ER model to the relational model, each strong entity would be represented as a new table. Additionally, a tuple can be mapped as an entity instance in the database. In relation to the weak entity, the use of the foreign key is defined, and each corresponding attribute is made unique.
Regards,
Ricardo
References
Taylor, A. (2019). Converting an E-R model into a relational model. Introducing SQL and Relational Databases. https://doi.org/10.1007/978-1-4842-3841-7_13
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