Enhanced Entity-Relationship (EER) Model – Lecture Review

These flashcards review key concepts, notation, constraints, examples, and practical considerations of the Enhanced Entity-Relationship (EER) model, entity clustering, and packaged data models as covered in the lecture.

What primary purpose does the Enhanced Entity-Relationship (EER) model serve beyond the basic E-R model?

It extends the basic E-R model to better handle complex business data and relationships such as supertype/subtype hierarchies and entity clustering.

In EER, what is a supertype?

A generic entity type that is related to one or more specialized entity types called subtypes.

In EER, what is a subtype?

A meaningful subgrouping of entities within a supertype that inherits its attributes and relationships, but may also have its own unique ones.

How do subtypes obtain the attributes of their supertype?

Through inheritance; subtypes automatically inherit all attributes and relationships of their supertype.

Which modeling choice exploits common properties while still recognizing distinct ones for employee categories?

Creating a supertype EMPLOYEE with subtypes HOURLY EMPLOYEE, SALARIED EMPLOYEE, and CONSULTANT.

Give an example of a common attribute shared by all EMPLOYEE subtypes in the lecture example.

Employee Number (other acceptable answers: Employee Name, Address, Date Hired).

What EER technique helps simplify very large E-R diagrams by grouping related entities and relationships?

Entity clustering.

Why might data modelers explicitly draw supertypes and subtypes in an E-R diagram?

To make relationships, cardinalities, and constraints more explicit and meaningful.

Define generalization in the context of EER.

A bottom-up process that defines a more general entity type from a set of more specialized entity types.

Define specialization in the context of EER.

A top-down process that defines one or more subtypes from an existing supertype based on distinguishing characteristics.

Which symbol indicates a disjointness constraint in an EER diagram?

A "d" inside the circle connecting the supertype to its subtypes.

Which symbol indicates an overlap constraint in an EER diagram?

An "o" inside the circle connecting the supertype to its subtypes.

What does the Total Specialization Rule require?

Every instance of the supertype must be a member of at least one subtype (double line notation).

What does the Partial Specialization Rule allow?

An instance of the supertype may exist without belonging to any subtype (single line notation).

When would you choose to model subtypes? Name one of the two main conditions.

When attributes apply to some but not all instances of an entity type OR when instances of a subtype participate in a unique relationship.

What is a subtype discriminator?

An attribute of the supertype whose values determine to which subtype(s) each instance belongs.

Provide an example of a subtype discriminator from the lecture.

EMPLOYEE.Employee Type coded as H (Hourly), S (Salaried), or C (Consultant).

How is a discriminator modeled for overlapping subtypes in the PART example?

As a composite attribute with Boolean components Manufactured? and Purchased? each storing Y/N.

What is an EER supertype/subtype hierarchy?

A hierarchical arrangement where each subtype has exactly one supertype, and subtypes may themselves be supertypes of further subtypes.

In the university HR example, which entity is the root of the hierarchy?

PERSON.

Name the subtypes directly under PERSON in the university HR model.

EMPLOYEE, STUDENT, and ALUMNUS.

Under EMPLOYEE in the university HR model, what two subtypes are defined?

FACULTY and STAFF.

What specialization constraints apply to FACULTY and STAFF?

Partial specialization and disjoint rule (an employee may be neither, but cannot be both).

What specialization constraints apply to GRADUATE STUDENT and UNDERGRAD STUDENT?

Total specialization and disjoint rule (every student is one of the two, but not both).

Why is attribute assignment pushed to the highest logical level in a hierarchy?

So the attribute can be shared by as many subtypes as possible, reducing redundancy.

Define entity clustering in one sentence.

A technique that groups related entity types and relationships into higher-level abstract entities to provide a macro-level view and simplify large models.

List two example clusters from the Pine Valley Furniture model.

SELLING UNIT, CUSTOMER, ITEM SALE, ITEM, MANUFACTURING, or MATERIAL (any two).

What is functional decomposition and how does it relate to entity clustering?

An iterative approach to breaking down a system into related components; entity clustering is a form of functional decomposition applied to data models.

What are packaged data models?

Predefined universal or industry-specific data models that can be customized to fit an organization’s business rules.

Give two advantages of using packaged data models.

Faster project timelines, reduced cost, proven components, up-to-date with standards, error reduction, holistic view, readability, or easier vendor integration (any two).

What crucial artifact comes with a purchased data model and helps in understanding it?

Metadata describing the model, usually inside a structured data-modeling tool.

What is data profiling in the context of customizing a packaged model?

Analyzing existing data to uncover patterns, inconsistencies, and hidden business rules for better model alignment and data quality.

Describe the PARTY – PARTY ROLE – PARTY RELATIONSHIP pattern.

PARTY represents persons or organizations; PARTY ROLE captures a party in a specific role; PARTY RELATIONSHIP is an associative entity that links multiple parties in their roles.

Why does the PARTY ROLE entity simplify large subtype structures?

It distinguishes the actor (PARTY) from the various roles it may play over time, reducing the need for extensive subtyping of PARTY.

In packaged models, how are most strong entities linked for flexibility?

With many-to-many relationships via associative entities.

What rule about specialization and overlap do universal data models typically follow?

All supertype/subtype relationships are modeled with total specialization and overlap to maximize completeness and flexibility.

What is the role of business-rule verification when adopting a packaged model?

Reviewing each rule with subject matter experts to confirm it fits the organization, adjusting or discarding rules as necessary.

Explain the difference between disjointness and completeness constraints using one sentence each.

Disjointness determines whether a supertype instance can belong to multiple subtypes simultaneously; completeness determines whether a supertype instance must belong to at least one subtype.

What notation shows the Total Specialization Rule in Visio?

A double line under the category circle connecting the supertype to its subtypes.

Give an example of a disjoint constraint from the hospital case.

A patient can be either OUTPATIENT or RESIDENT PATIENT but not both at the same time (disjoint).

Give an example of an overlap constraint from the part case.

A PART can be both MANUFACTURED and PURCHASED simultaneously (overlap).

What main benefit does entity clustering give to different user communities?

It allows each community to focus on only the clusters relevant to its interests, providing multiple tailored views of the overall model.

Why is the role of data modeler compared to moving from artisan to engineer?

Because modelers increasingly adapt pre-engineered packaged models instead of crafting every model from scratch, emphasizing efficiency and standards.

State one reason universal data models make inter-organizational data sharing easier.

They use standardized structures and terminology that multiple companies within an industry can adopt, facilitating compatibility.

What is aggregation in EER, and give the example cited.

A relationship where an entity is composed of other entities; e.g., a PC composed of disk drive, RAM, and motherboard.

Summarize when supertype/subtype relationships are most useful.

When certain attributes or relationships apply only to some instances of an entity type, or when those instances participate in unique relationships.