ITM 310: Chapter 3

Advantages of Packaged Data Models

-Use proven model components. -Save time and cost. -Less likelihood of data model errors. -Easier to evolve and modify over time. -Aid in requirements determination. -Easier to read. -Supertype/subtype hierarchies promote reuse. -Many-to-many relationships enhance model flexibility. -Vendor-supplied data model fosters integration with vendor's applications. -Universal models support inter-organizational systems.

Disjointness Constraint

A Constraint that addresses whether an instance of a supertype may simultaneously be a member of two (or more) subtypes.

Universal Data Model

A generic or template data model that can be reused as a starting point for a data modeling project. *Also called a "Pattern"

Supertype/Subtype Hierarchy

A hierarchical arrangement of supertypes and subtypes in which each subtype has only one supertype.

False

A subtype is a generic entity that has a relationship with one or more entities at a lower level. T/F

True

Because a purchased data model is extensive, you begin by identifying the parts of the data model that apply to your data modeling situation. T/F

The business environment has drastically changed since the relational model was first introduced in the 1970s. Business relationships are more complex, and organizations must have ways to represent data to represent the complexity. Organizations must be prepared to segment their markets as well as customize their products. The enhanced E-R model has evolved to represent these changes and also is similar to the object-oriented data model.

Explain why the E-R model needed to be expanded into the enhanced E-R model.

A packaged data model is quite extensive, so you would begin with the part of the data model that you will use for your situation. You would start first with entities, then attributes and then relationships. The next step is to rename the data elements to terms that are meaningful to your organization. Since the packaged data model may be used to replace an existing system, the next step is to map the packaged model to the current database. This mapping will be used later for data migration. Perhaps the most challenging step is to determine the business rules for the new system.

How is the data modeling process different when starting with a purchased solution?

Supertypes

In a supertype/subtype hierarchy, subtypes that are lower in the hierarchy inherit attributes from not only their immediate supertype but from all ________ in the hierarchy.

True

It is easy to miss the opportunity to visualize future requirements shown in the full data model when using a packaged data model. T/F

Packaged Data Models

Predefined Data Models. -Could be Universal or Industry-Specific. -Often are Customizable *Can buy them and they are based on best practices.

Supertype

Relationships at the _________________________ level indicate that all subtypes will participate in the relationship.

There are attributes that apply to some but not all instances of an entity type.

Subtypes should be used when:

Subtype

The instances of a_______________ may participate in a relationship unique to that subtype. In this situation, the relationship is shown at the subtype level.

True

The most important challenge of customizing a purchased data model is determining the business rules that will be established through the data model. T/F

Determining the business rules that will be established through the data model.

The most important challenge of customizing a purchased data model is:

Supertype

Which of the following is a generic entity type that has a relationship with one or more subtypes?

Most organizations can no longer afford to have data models developed in house, both in terms of labor costs as well as time. As such, the role of data modeler is evolving from artisan to that of engineer. A packaged data model allows one to customize an organization's database needs using a superset of the model needed by the organization.

Why are packaged data models gaining popularity?

False

You will never need to map data in current databases to data in a packaged data model. T/F

Supertype

A generic entity type that has a relationship with one or more subtypes.

Enhanced Entity Relationship Model (EER)

A model that has resulted from extending the original E-R model with new modeling constructs.

Attribute Inheritance

A property by which subtype entities inherit values of all attributes and instances of all relationships of their super type. -An instance of a subtype is also an instance of the supertype.

Partial Specialization Rule

A rule that specifies that an entity instant of a super type is allowed not to belong to any subtype. *Single Line

Disjoint Rule

A rule that specifies that an instance of a super type may not simultaneously be a member of two (or more) subtypes.

Overlap Rule

A rule that specifies that an instance of a super type may simultaneously be a member of two (or more) subtypes.

Total Specialization

A rule that specifies that each entity instance of a supertype must be a member of some subtype in the relationship. *Double Line

Entity Cluster

A set of one or more entity types and associated relationships grouped into a single abstract entity type.

Subtype

A subgrouping of the entities in an entity type that is meaningful to the organization and that shares common attributes or relationships distinct from other subgroupings.

Subtype Discriminator

An attribute of a super type whose values determine the target subtype or subtypes. *The attribute tells you which subtype to put the data in.

It is best to use a supertype/subtype hierarchy when there are attributes that apply to some but not all instances of an entity type. For example, if we have an employee entity type and there is an hourly wage attribute that only applies to hourly employees, it may be best to use a supertype/subtype relationship. Another reason for using supertype/subtype relationships is when you have instances of a subtype that participate in a relationship unique to that subtype. For example, if we have a contractor subtype of employee that has a relationship with staffing agency, then it would be best to use supertype/subtype relationship.

Discuss the reasoning behind using supertype/subtype relationships.

A subtype is an entity which represents data meaningful to the organization. For example, an undergraduate student and a graduate student might be a subtype. A supertype is a generalization of various subtypes and contains attributes which are common to both. Supertypes and subtypes may have relationships with other entities. Also, a subtype inherits the attributes of its supertype.

Explain the terms subtype and supertype. Discuss the differences between them.

Completeness Constraint

A type of Constraint that addresses whether an instance of a super type must also be a member of at least one subtype.

False

Adapting a packaged data model from your DBMS vendor makes it difficult for the application to work with other applications from the same vendor. T/F