Entity types and its attributes
- Discuss how to distinguish between an entity type and an attribute
- Give an example of three entity types and accompanying attributes that might be associated with a database for a car rental agency.
- What is a relationship type? How does a relationship type differ from a relationship instance?
- What is meant by the “degree” of a relationship?
- What is the value of using role names to describe the participation of an entity type in a relationship type?
- What is the difference between a binary relationship that exhibits a 1:1 cardinality constraint and a binary relationship that exhibits
The report discusses the different topics related to entity types and its attributes. First of all, the report demonstrates the difference between the entity type and an attribute. It provides the introduction about entity type that demonstrates the data which is related to some person, organization or concept. The report also explains about the attributes which are also a significant part of explaining the relationship between two or more entities because it presents the specific characteristics of the different entity types. Secondly, it describes different entity types, then it provides the information regarding relationship type and degree of relationships. In the last, it defines the importance of role name in an entity type.
It is known as a set of entities that have the same attributes. Each entity type in a database is recognized by a name and a list of various types of attributes. An entity denotes a person, place, object, or thing. (IBM, 2016) For example, the employee is considered to be an entity type in which his/her name, age, and salary are mentioned as its attributes.
In the entity connection modeling, the characteristics of various types of entities are called attributes. On the other hand, attributes are a subgroup of information or some kind of object that mainly represents the specific type of entity. It defines the occurrences of an individual and helps to distinguish between each occurrence by demonstrating it’s all characteristics. (IBM, 2016)
|Entity type represents the real world object or things which is unique and independent. (Więch & Krycuń, 2015)||Attributes demonstrate the specific properties of entities. (Więch & Krycuń, 2015)|
|Each row in database table represents the individual occurrence in an entity.||While attributes are represented as a column in database tables.|
|The entity defines the thing that exists independently.||Attributes define the individual instances.|
|Example, in a Worker database, each row resembles the records of an individual worker of the organization, where ‘worker’ is an entity.||Example, attributes of the entity ‘worker’ represents the significant characteristics of a such as its age, salary, rank, and department.|
Example of three entity types related to the attributes of car rental agency
An organization records the information of its employees or staff, clients, products, etc. so that could record the data into one database. Examples of entity types related to attributes of car rental agency are employee, client, and car.
Employees are the important perspectives of any organization or a company. Suppose, in a car rental agency management system, ‘employee’ is an entity and its various attributes would be employee name, age, salary, employee ID, date of birth, designation, etc. Similarly, ‘client’ is an entity and its related attributes are client name, client ID, address, contact, Order number, Car model, car color, etc. When the object or thing is sold to some customers, it is necessary to record its details and other specifications of the product. In a car rental agency management system, ‘car’ is an entity and its various attributes would be color, model, price, etc.
A relationship type R shows the different types of entities i.e. E1, E2, and En. En is a set of relations that demonstrate the relationship between those entities. In the case of entity types or sets, a relationship type and its corresponding relationships are commonly referred by the same name (Elmasri, 2017). R is a set of relationship instances where each ri is the tuple of entities and on the other hand, each entity is a member of the entity type.
A relationship type is different from relationship instance because it represents the numerous types of entities by demonstrating its name and some other significant characteristics. But the relationship instance is that which associated or connected with an entity from a one entity type to another entity of entity types. It establishes the relationship between various participating entity types (Elmasri, 2017).
“Degree” of a relationship
The degree of relationship is referred as quantity of occurrences which is present in one object and these are connected with the quantity of occurrences in another entity. It also indicates that how many entity modules are mainly contributing to the relationship. It states that if two entity classes are in the relationship then it is said to be the degree two and it referred to as a binary relationship. On the other hand, if there are three entity classes occurring in the relationship then it is said to be the degree three and it is known as a ternary relationship. For example, if we have the two objects or entities in a relationship i.e. customer and product, then it is said to be the degree of two and they have a binary relationship.
There are mainly three types of degree of relationship that are mention below-
- One to one
- One to many
- Many to many
Importance of role name
The participation of an entity type in a relationship type is always represented by its role name. On the other hand, when it is used in the recursive relationship types then the role name describes the functions of the participation in each entity type. These are also used when two entity types are connected with more than one relationship type. For example, the Nurse is an entity and the use of role name would denote the Manages relationship type. The participation of Nurse with role name manages to reflect that nurse may manage other staff nurses. So, it represents that use of role names can help to clarify the participation of an entity in the relationship type. (Thalheim, 2011)
Binary relationship that exhibits a 1:1 cardinality constraint and a binary relationship that exhibits 1: n cardinality constraint
In a binary relationship that exhibits a 1:1 cardinality ratio, each occurrence of entity type E1 is associated with at most one occurrence of entity type i.e. E2 and a vice versa. On the other hand, the binary relationship that exhibits a 1: n cardinality constraint, the relationship occurrence of each entity type i.e. E1 is connected or associated one time. While the occurrence of each entity type i.e.is E2 is associated with at most one existence of object type i.e. E1.
The report provides a brief information about the entity and its types that how they are necessary or useful to represent the relation of some individual, place or object within its environment. We can take advantageous information about entity types, attributes, and relationship types explained in this report.
Elmasri, R., & Navathe, S. B. (2017). Relationship Types, Relationship Sets, Roles, and Structural Constraints – study Material lecturing Notes assignment reference wiki description explanation brief detail. Retrieved September 22, 2017, from http://www.brainkart.com/article/Relationship-Types–Relationship-Sets–Roles–and-Structural-Constraints_11431/
IBM. (2016). Key concepts: Entity, attribute, and entity type. Retrieved from https://www.ibm.com/support/knowledgecenter/en/SSWSR9_11.6.0/com.ibm.mdmhs.overview.doc/entityconcepts.html
Thalheim, B. (2011). The Enhanced Entity-Relationship Model. Handbook of Conceptual Modeling, 165-206. doi:10.1007/978-3-642-15865-0_6
Więch, A., & Krycuń, A. K. (2015, December 1). Database Modeling Course (2): Entities and Attributes. Retrieved from http://www.vertabelo.com/blog/technical-articles/database-modeling-course-entities-and-attributes