The Entity Relationship Model

“The Entity Relationship Model” Please respond to the following:

Defining relationships within a database can improve search capabilities and optimal performance of the database in the long run. Identify at least two relationship strength types that can be used within the entity relationship model.

There are two types of relationship strengths types between entities: weak, or non-identifying, and strong, or an identifying relationship. According to the textbook “the relationship strength is based on how the primary key of a related entity is defined”. It is important to understand that both a primary key and foreign key, can be not just one, but a combination of attributes, this is essential to understand relationship strengths.

In a relationship, the primary key of one entity appears as a foreign key in the related entity. In the case of a weak relationship, the parent entity primary key is not part of the child’s primary key, but only a foreign key. A foreign key on the child entity does refer to the parent one, but since is not part of the combination of primary key attributes, it is determine as a weak relationship.

On the other hand, a strong relationship occurs when on the child entity, its primary key contains one or more elements of the parent primary key. In other words, there is an attribute, or attributes that is present on the primary key of both entities in the relation.

Using the classifications from part one of this discussion; provide a real word scenario that demonstrates each relationship strength classification.

On a database for the Human Resources department on any organization, the relationship and its strengths can be easily identified. Take for example the following simple entities:

EESimpleInfo (empID, empFirstName, empLastName)

ManagerInfo (mgrID, empID, mgrFirstName, mgrLastName)

Department (deptID, deptDescription, mgrID)

EESimpleInfo contains basic info for any given EE in the organization, while managerInfo contains information for any manager. Meanwhile, the department table contains information about all the departments in the company, and who is their respective manager.

The relationship between EESimpleInfo and ManagerInfo is a strong relationship, since the primary key of the child includes a primary key element of the parent entity. The primary key for the child been the combination of both the manager ID and the manager’s respective employee ID. On the other hand, the relationship between manager info and department is a weak one, since the relationship is established by the manager ID, but its reference only by a foreign key on the child entity.

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