Database Systems Assignment
91.3902 Database Systems
Assignment #1
1. Discuss the role of a high-level data model in the database design process. High-level data models assist in conceptual design and helps express data requirements of the users and includes detailed descriptions of the entity types, relationships, and constraints. The high-level data model is also used as a reference to ensure that all users’ data requirements are met and that the requirements do not include conflicts.
2. List the various cases where use of a null value would be appropriate. Null value would be appropriate when a particular entity does not have an applicable value for an attribute. There are two cases for such situations. The first case arises when it is known that the attribute value exists but is missing. An example for cases like such would be if the Height attribute of a person is listed as null. The second case arises when it is not known whether the attribute value exists. An example would be is the HomePhone attribute of a person is null.
3. Define the following terms: entity, attribute, attribute value, relationship instance, composite attribute, multivalued attribute, derived attribute, complex attribute, key attribute, value set (domain).
Entity Entity is a “thing” in the real world with an independent existence. It can also be an object with physical existence (i.e. person, car) or conceptual existence (i.e. company, job).
Attribute An attribute is a particular property that describes entity (i.e. person name company name).
Attribute Value Attribute values are major data stored in the database.
Relationship Instance Relationship Instance is an association of entities, where the association includes exactly one entity from each participating entity type.
Composite Attribute Composite attribute is an attribute that can be divided into meaningful components.
Assignment #1
1. Discuss the role of a high-level data model in the database design process. High-level data models assist in conceptual design and helps express data requirements of the users and includes detailed descriptions of the entity types, relationships, and constraints. The high-level data model is also used as a reference to ensure that all users’ data requirements are met and that the requirements do not include conflicts.
2. List the various cases where use of a null value would be appropriate. Null value would be appropriate when a particular entity does not have an applicable value for an attribute. There are two cases for such situations. The first case arises when it is known that the attribute value exists but is missing. An example for cases like such would be if the Height attribute of a person is listed as null. The second case arises when it is not known whether the attribute value exists. An example would be is the HomePhone attribute of a person is null.
3. Define the following terms: entity, attribute, attribute value, relationship instance, composite attribute, multivalued attribute, derived attribute, complex attribute, key attribute, value set (domain).
Entity Entity is a “thing” in the real world with an independent existence. It can also be an object with physical existence (i.e. person, car) or conceptual existence (i.e. company, job).
Attribute An attribute is a particular property that describes entity (i.e. person name company name).
Attribute Value Attribute values are major data stored in the database.
Relationship Instance Relationship Instance is an association of entities, where the association includes exactly one entity from each participating entity type.
Composite Attribute Composite attribute is an attribute that can be divided into meaningful components.