9

Ace your homework & exams now with Quizwiz!

IF one, M (Mandatory) THEN participation in the relationship by the entity is mandatory, and at least one entity instance must participate in the relationship. True or False

True

IF zero, O (optional) THEN participation in the relationship by the entity is optional, and no entity instance must participate in the relationship. True or False

True

In a one-to-many relationship: -The entity on the one side of the relationship is called the parent entity or just the parent. -The entity on the many side of the relationship is called the child entity or just the child. True or False

True

Minimums are generally represented as either zero or one in E-R diagrams (but written with a O for optional or M for mandatory): True or False

True

Relationships connecting supertypes and subtypes are called IS-A relationships, because a subtype is a supertype. True or False

True

The ID-dependent entity is a logical extension or subunit of the parent: True or False

True

The principal difference between an entity and a table (relation) is that you can express a relationship between entities without using foreign keys True or False

True

The supertype contains all common attributes, while the subtypes contain specific attributes True or False

True

Two entities have a binary relationship of degree two. True or False

True

•If subtypes are exclusive, one supertype relates to at most one subtype. True or False

True

•If subtypes are inclusive, one supertype can relate to one or more subtypes. True or False

True

•Subtypes are used to avoid value-inappropriate nulls. (Why give a undergraduate student a null value for GMAT score? It's not that the test is missing from their records, it's that the test is inappropriate for admission as an undergrad. So to avoid this we create subtypes.) True or False

True

•The identifier of the supertype and all of its subtypes must be identical; i.e., the identifier of the supertype becomes the identifier of the related subtype(s). True or False

True

Identifiers

are attributes that name, or identify, entity instances.

Composite identifiers

are identifiers that consist of two or more attributes.

Relationship classes:

associations among entity classes

Relationship instances:

associations among entity instances

Information Engineering (IE)

by James Martin (1990); uses "crow's foot" notation, is easier to understand, and we will use it

Original E-R model

by Peter Chen (1976)

Unified Modeling Language (UML)

by the Object Management Group; it supports object-oriented methodology [see Appendix C]

Entity instance

the occurrence of a particular entity

The degree of the relationship is not the number of entity classes in the relationship True or False

False

Three entities have a ternary relationship of degree two True or False

False degree of three

The subtypes may have a discriminator attribute which indicates the subtype True or False

False supertype may have a discriminator attribute

Minimum cardinality

is the minimum number of entity instances that must participate in a relationship.

The Three Phases of Database Design are

Conceptual schema (E-R Model) Logical schema (relational model) Physical schema

All ID-Dependent entities are not considered weak True or False

False

There are three types of maximum cardinality:

One-to-One [1:1] One-to-Many [1:N] Many-to-Many [N:M]

Physical schema

Tables Columns and data types Database rules: e.g. referential integrity constraint Foreign Key / Primary key

A data model is a plan or blueprint for a database design. True or False

True

A data model is more generalized and abstract than a database design. True or False

True

All entity instances of a given entity class have the same attributes but change in the values of those attributes. True or False

True

Entity class

a collection of entities of a given type

IDEF1X

a national standard developed by the National Institute of Standards and Technology [see Appendix B]

Attributes

describe an entity's characteristics.

Extended E-R model

extensions to the Chen model

Entity-Relationship model

is a set of concepts and graphical symbols that can be used to create conceptual schemas.

A subtype entity

is a special case of a supertype entity:

ID-dependent entity

is an entity (child) whose identifier includes the identifier of another entity (parent).

A weak entity

is an entity whose existence depends upon another entity.

Maximum cardinality

is the maximum number of entity instances that can participate in a relationship.

What is the advantage of learn E-R model

•Communication - between developers •Documentation—for maintenance/future projects and for liability...we may need to show standard design practices were used in the construction of the databases

Conceptual schema (E-R Model)

•Entities •Attributes •Relationships and Cardinality •Identifiers

Logical schema (relational model)

•Relations •Attributes •Functional dependencies •Determinants

Cardinality

•Relationships in the E-R model are classified by their cardinality •means "count" and is expressed as a number


Related study sets

Risk Analysis Techniques Chapter 11

View Set

PART 1 (FINGER, THUMB, & HAND) Radiographic Procedures 2: Chapter 4 Upper Limb

View Set

Oncology and hematological problems

View Set