Management: Employer and Employee
3. Answer the following questions concerning Figure 2-22.
a) Where is a unary relationship, what does it mean, and for what reasons might the cardinalities on it be different in other organizations?
A unary relationship is shown with the EMPLOYEE entity; An EMPLOYEE Supervises 0:M EMPLOYEEs, An EMPLOYEE Is Supervised By 0:1 EMPLOYEE. This relationship tells us that we can determine what employees are supervised by another employee, as well as determine which employees are supervisors in this company.
In other organizations, there may be different policies regarding employee supervision that could cause the data relationships among EMPLOYEE instances to be different. For instance, another company might allow an employee to have multiple supervisors (e.g., in an organization with a matrix structure).
b) Why is Includes a one-to-many relationship and why might this ever be different in some other organization?
Includes is a one-to-many (1:M) relationship because of the business rules that PVFC has in place: “a product line may group any number of products but must group at least one product; and each product must belong to exactly one product line.” Another organization may have other business rules that could permit a product being assigned to more than one product line (changing Includes to a M:N relationship). Alternatively, another organization might also show Includes as a (1:M) overall relationship but might permit the establishment of a PRODUCT LINE without identifying PRODUCTs that belong to this group (e.g., thus permitting an optional minimum cardinality on the PRODUCT side of the Includes relationship).
c) Does Includes allow for a product to be represented in the database before it is assigned to a product line (e.g., while the product is in research and development)?
No, Figure 22 shows that the PRODUCT must be Included in at least 1 PRODUCT LINE by the mandatory 1 and only 1 cardinality notation near the PRODUCT LINE portion of the Includes
a) Where is a unary relationship, what does it mean, and for what reasons might the cardinalities on it be different in other organizations?
A unary relationship is shown with the EMPLOYEE entity; An EMPLOYEE Supervises 0:M EMPLOYEEs, An EMPLOYEE Is Supervised By 0:1 EMPLOYEE. This relationship tells us that we can determine what employees are supervised by another employee, as well as determine which employees are supervisors in this company.
In other organizations, there may be different policies regarding employee supervision that could cause the data relationships among EMPLOYEE instances to be different. For instance, another company might allow an employee to have multiple supervisors (e.g., in an organization with a matrix structure).
b) Why is Includes a one-to-many relationship and why might this ever be different in some other organization?
Includes is a one-to-many (1:M) relationship because of the business rules that PVFC has in place: “a product line may group any number of products but must group at least one product; and each product must belong to exactly one product line.” Another organization may have other business rules that could permit a product being assigned to more than one product line (changing Includes to a M:N relationship). Alternatively, another organization might also show Includes as a (1:M) overall relationship but might permit the establishment of a PRODUCT LINE without identifying PRODUCTs that belong to this group (e.g., thus permitting an optional minimum cardinality on the PRODUCT side of the Includes relationship).
c) Does Includes allow for a product to be represented in the database before it is assigned to a product line (e.g., while the product is in research and development)?
No, Figure 22 shows that the PRODUCT must be Included in at least 1 PRODUCT LINE by the mandatory 1 and only 1 cardinality notation near the PRODUCT LINE portion of the Includes