ACG4401 Chapter 5
Multiple Choice Questions
1C 2E 3B 4E 5B 6B 7D 8C 9E 10D 11C 12B 13D 14A 15D
Explain the difference between conceptual, logical, and physical database models.
A conceptual model attempts to represent reality as faithfully as possible and is independent of any particular type of database model, software or hardware. A logical model represents reality in a format compatible with a specific type of database, such as relational or object-oriented. A logical model is independent of any particular type of hardware and may be implemented in any software that conforms to the logical model type. For example, a relational logical model may be implemented using a number of different relational database software packages but it may not be implemented using object-oriented database software. A physical database model represents the actual implementation of the logical model in conformance with a specific software package's requirements. For example, a model that portrays the specifications of a database implemented in Microsoft Access is a physical database model.
What is the purpose of a primary key attribute
A primary key uniquely and universally identifies each instance of a class
What is the purpose of a foreign key?
Foreign keys are key attributes of an object that are posted into another object table. The sole purpose of foreign keys is to link tables so the tables can be used collectively to store business data and to generate useful information
Given the conceptual model of the association between Alpha and Omega, if 74% of alphas are related to omegas and 46% of omegas are related to alphas, what is the best relational table implementation .
Look at the word document
Given the tables below and assuming entered data conforms to the multiplicities, what must have been the underlying conceptual model?
Look at the word document
What are the multiplicities for a class that has mandatory participation in an association and can be related to at most one instance of the associated class? Where should these multiplicities be placed on the UML class diagram?
Minimum = 1; maximum = 1; the 1..1 should be placed next to the associated class on the UML class diagram (i.e., on the opposite side of the association from the class whose participation they describe).
How are minimum multiplicities used when designing enterprise systems?
Minimum multiplicities are used to represent and model business rules; they indicate whether a class's participation in an association is optional or mandatory
Does every table in a relational database contain a foreign key? Explain
No. Foreign keys can only be posted into tables for which the class' participation in a relationship has a maximum of 1. Most resource and agent tables will not contain foreign keys because they can participate many times in the associations with related events. Sometimes they may have foreign keys representing associations with other agents or resources (e.g. customer may have a salesperson identifier posted as a foreign key to represent the one salesperson that is assigned responsibility for the customer).
What is referential integrity and how can one tell if a relational database has referential integrity?
Referential integrity is a principle in the relational database model that requires a value for a foreign key attribute to either be null (blank) or to match exactly one of the data values in the table in which the attribute is a primary key. Referential integrity may be enforced in Microsoft Access by marking the appropriate relationship property checkbox in the relationship layout.
How are maximum multiplicities used when designing enterprise systems
maximum multiplicities are used to communicate the maximum number times a class can participate in an association