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Questions and Answers
A dependent entity exists only when it is related to a ______ entity.
parent
Surrogate primary keys are especially helpful when there is no ______ key.
natural
A unique index and not null constraints should be used if you use a ______ key.
surrogate
In a 1:1 relationship, a foreign key is placed on the 'many' side of the ______ relationship.
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Data modeling and design requires skills acquired through ______.
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The proper identification of ______ keys is essential for flexible database design.
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In implementation of relationships, foreign keys work with ______ keys.
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Experience in database design is acquired through ______.
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The result of adding more semantic constructs to the original entity relationship model is called the ______ model.
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An EER diagram is also known as an ______.
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An entity supertype is a generic entity type related to one or more entity ______.
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Entity subtypes contain unique ______ of each entity subtype.
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At the end of this module, students are expected to identify the main characteristics of entity relationship ______.
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Partial completeness is symbolized by a circle over a single ______.
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Specialization is a top-down process that identifies more specific entity ______ from higher-level entity supertype.
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Generalization identifies more generic entity supertype from lower-level entity ______.
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Entity clustering is considered 'virtual' because it is not actually an entity in the final ______.
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Total completeness is symbolized by a circle over a double ______.
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Every subtype has only one ______ to which it is directly related.
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Subtypes exist only within the context of their ______.
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Entity subtypes inherit attributes and relationships from their ______.
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The subtype discriminator is an attribute in the ______ entity.
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Disjoint subtypes are also called ______ subtypes.
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Subtypes can have many levels of ______/subtype relationships.
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Entity subtypes inherit their primary key attribute from their ______.
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Overlapping subtypes contain ______ subsets of the supertype entity set.
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The primary key’s function is to guarantee ______ integrity.
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A natural key is a ______ identifier used to uniquely identify real-world objects.
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Primary keys and ______ keys work together to implement relationships.
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A composite primary key is useful as identifiers of ______ entities.
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The main function of a primary key is to uniquely identify an entity instance or ______ within a table.
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A surrogate key is an alternative to using a ______ key as the primary key.
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______ keys implement relationships among entities behind the scenes.
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Using composite primary keys helps ensure that there cannot be ______ values.
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Study Notes
Identifiers and Surrogate Keys
- Weak entities depend on other entities for existence; they do not exist outside a parent-child relationship.
- Surrogate primary keys are beneficial when there is:
- No natural key available.
- A candidate key with complex semantic content.
- A candidate key that is excessively long or cumbersome.
- When using surrogate keys:
- Ensure the candidate key functions correctly.
- Implement “unique index” and “not null” constraints for integrity.
Data Modeling and Design
- Data modeling requires practical skills developed through experience and practice.
- Four key design cases emphasize:
- The need for flexible design.
- Accurate primary key identification.
- Correct placement of foreign keys.
Design Case 1: 1:1 Relationships
- Foreign keys are essential for establishing relationships in a relational model.
- Place the primary key of the parent entity onto the dependent child entity as a foreign key.
- In 1:1 relationships, a foreign key can either:
- Be placed in both entities (not recommended), or
- Reside in only one entity, referencing the primary key of the other.
Extended Entity Relationship (EER) Model
- EER models enhance the basic ER model with additional semantic constructs.
- EER diagrams (EERDs) represent this advanced modeling.
Entity Supertypes and Subtypes
- Supertype: A generic entity with common characteristics shared by one or more subtypes.
- Subtype: A specific entity containing unique attributes pertaining to the subtype.
Specialization Hierarchy
- Illustrates the relationship between supertypes and subtypes, represented as “IS-A” relationships.
- Each subtype is strictly defined within its supertype context.
- Supertypes can have multiple levels of hierarchical relationships.
Inheritance
- Subtypes inherit attributes and relationships from their supertype.
- Each subtype receives its primary key attribute from the supertype.
- Implementation maintains a 1:1 relationship between supertypes and subtypes.
Subtype Discriminator
- An attribute in the supertype that distinguishes which subtype an instance belongs to.
- By default, comparison is performed with equality but can involve other conditions.
Disjoint and Overlapping Constraints
- Disjoint Subtypes: Unique subsets of the supertype.
- Overlapping Subtypes: Nonunique subsets that can share members from the supertype.
Completeness Constraints
- Addresses whether occurrences of the supertype must belong to at least one subtype.
- Partial Completeness: Indicates some supertype instances may not have a subtype (represented with a circle over a single line).
- Total Completeness: Indicates all supertype instances must belong to at least one subtype (represented with a circle over a double line).
Specialization and Generalization
- Specialization: A top-down approach identifying specific subtypes from a supertype based on unique characteristics.
- Generalization: A bottom-up approach defining a generic supertype from lower-level subtypes by grouping common attributes.
Entity Clustering
- Represents multiple entities and relationships using a "virtual" entity type in an ERD.
- Functions as a temporary entity to avoid displaying attributes directly.
Entity Integrity and Primary Keys
- The primary key uniquely identifies each entity instance, ensuring entity integrity.
- Primary keys and foreign keys jointly maintain relational integrity.
- Proper selection of primary keys significantly affects database efficiency.
Natural Keys and Primary Keys
- Natural keys represent real-world identifiers familiar to users, often serving as primary keys.
- Alternatively, composite primary keys or surrogate keys may be utilized.
Primary Key Guidelines
- Primary keys may consist of single or multiple attributes.
- Their main role is to identify instances uniquely and guarantee entity integrity.
- Primary keys must be distinct and not used to describe the entity.
Composite Primary Keys
- Useful for:
- Identifying composite entities in M:N relationships.
- Establishing weak entities with a strong identifying relationship with their parent entities.
- Provide an automatic mechanism to prevent duplicate values.
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Description
Explore the concepts of weak entities and identifying relationships in information management. This quiz will test your understanding of how dependent entities relate to their parent entities in a data model. Dive deep into the intricacies of real-world object representation.
