Entity-Relationship (ER) Model Quiz

Data Modeling Using the Entity-Relationship (ER) Model 21 October 2019 Lecture 4 Dr. Ahmed Alnasheri Dr. Ahmed Alnasheri Objectives  Understand concepts of data modeling and its purpose  Understanding the database design process  Introduce the major components of ER diagram  Learn how relationships between entities are defined  Learn how ERD components affect database design and implementation  Learn how to interpret the modeling symbols Dr. Ahmed Alnasheri 2 Data Model  Model: an abstraction of a real-world object or event – Useful in understanding complexities of the realworld environment  Data model – A diagram that displays a set of tables and the relationships between them – Next Slide: “Restaurant” Access data model using Entity Relationship Diagram (ERD) Dr. Ahmed Alnasheri 3 Access Data Model using ERD Dr. Ahmed Alnasheri 4 What is ER Model. And Why.  ER is modeling tool used to depict graphically a database design before it is actually implemented.  ER Model is used.

Relation = A table with columns and rows Attribute = A named column of a relation Cardinality = The number of tuples in a relation Domain = The set of allowable values for an attribute

Each cell of relation contains exactly one atomic value = Each entry in the table holds a single value Values of an attribute are all from the same domain = All values in a column belong to the same set of allowable values Each tuple is distinct; there are no duplicate tuples = No two rows are identical Order of attributes has no significance = The sequence of columns does not affect the data

Relation schema = Named relation defined by a set of attribute and domain name pairs Relational database schema = Set of relation schemas, each with a distinct name Database Relations = Collection of normalized relations with distinct relation names Relational Keys = Keys that uniquely identify tuples in a relation

Relation name is distinct from all other relation names in relational schema = Each table has a unique name within the database Each attribute has a distinct name = Every column is uniquely labeled within a table Order of tuples has no significance, theoretically = The sequence of rows does not affect the data Relational Database = A collection of normalized relations with distinct relation names

Relation = Each tuple is distinct; there are no duplicate tuples Attribute = Values of an attribute are all from the same domain Cardinality = The number of tuples in a relation Domain = The set of allowable values for an attribute