1. in the entity-relationship model, relationships can have attributes. t/f

2. attributes are the smallest division of data in er diagram. t/f

3.which level of abstraction is the er model most concerned with? a. external, b. conceptual, c. physical, d. internal

4. consider the following relationship involving two entities, students and classes: a student can take many classes. a class can be taken by many students.

how many tables can be used to represent this relationship in a schema? a. 1 b. 2 c. 3. d all of them

 1. True  2. True 3. Conceptual 4. 3 tables.

Explanation:

1. In the ER Model relationships can have attributes associated to them. For example in an organisation there is a one-to-one relationship between Employee and Department entities i.e. an Employee manages a Department and each Department is managed by some Employee. If you want to store the Start_Date from which the employee began to manage the department then you can give the Start_Date attribute to the relationship manages.

2. Attributes are the smallest division of data in the ER diagram. Attributes are used to describe an entity.For example an Employee entity can have the attributes Name, DateofBirth, Address, Salary. Attribute is represented by an oval with a name inside in ER diagram.

3. Conceptual  

Conceptual level is the highest level ER model as it contains less but defines the overall scope of the model.  It defines the data entities that are commonly used by the organization. A model on conceptual level of abstraction captures and represents business scope of the problem. It depicts the most important entities and the relationships between these entities.  A conceptual ER model can be used as the base for one or more logical data models. Conceptual level describes or defines the structure of the whole database. It hides details about the physical storage and concentrates on describing entities, relationships, etc.  It is part of the conceptual stage of database design and it provides a high-level data description.

4. 3 tables can be used to represent this relationship. One is a Student table. Second is the Class table. Now if we see the relationship. A student can take many classes. A class can be taken by many students. This is a many-to-many relationship between these two entities. It is not directly possible to implement this type of relationship in a database. To implement this relationship it has to be broken into 2 one to many relationships.  In order to do this, a new entity has to be created. So create one more table to establish a relationship between Student and Class entities. Primary keys of Student and Class tables are added into new table to create a composite primary key. This table can be named as Enrollment. Hence 3 tables are used.