Chapter 2 - Business Data Management
Entity-Relationship Diagram (E-R Diagram)
A graphical representation of an entity-relationship model
Entity-Relationship Model (E-R Model)
A logical representation of the data for an organization or for a business area, using entities for categories of data and relationships for associations between entities.
Relationship Type
A meaningful association between (or among) entity types
Entity
A person, a place, an object, an event, or a concept in the user environment about which the organization wishes to maintain data
True
T/F A multivalued attribute may take on more thank once value for a particular entity instance
True
T/F A time stamp is a time value that is associated with a data value
True
T/F Data names should always relate to business characteristics
True
T/F In an E-R diagram, an associative entity is represented by a rounded rectangle
True
T/F Participation is a relationship may be optional or mandatory
True
T/F Relationships represent action being taken using a verb phrase
False
T/F The degree of a relationship is the number of attributes that are associated with it
False
T/F The intent of a business rule is to break down business structure
False
T/F The purpose of data modeling is to document business rules about processes
False
T/F The relationship among the instances of three entity types is called a unary relationship
Entity Type
A collection of entities that share common properties or characteristics
Attribute
A property or characteristic of an entity or relationship type that is of interest to the organization
Unary Relationship
A relationship between instances of a single entity type
Binary Relationship
A relationship between the instances of two entity types
Cardinality Constraint
A rule that specifies the number of instances of one entity that can (or must) be associated with each instance of another entity.
Ternary Relationship
A simultaneous relationship among the instances of three entity types
Entity Instance
A single occurrence of an entity type
Business Rule
A statement that defines or constrains some aspect of the business. It is intended to assert business structure or to control or include certain the behavior of the business
Time Stamp
A time value that is associated with a data value, often indicating when some event occurred that affected the data value
Relationship Instance
An association between (or among) entity instances where each relationship instance associates exactly one entity instance from each participating entity type
Identifier
An attribute (or combination of attributes) whose value distinguishes instances of an entity type
Simple (or atomic) attribute
An attribute that cannot be broken down into smaller components that are meaningful to the organization
Composite Attribute
An attribute that has meaningful component parts (attributes).
Optional Attribute
An attribute that may not have a value for every entity (or relationship) instance with which it is associated
Multivalued attribute
An attribute that may take on more than one value for a given entity (or relationship) instance
Required Attribute
An attribute that must have a volume for every entity (or relationship) instance with which it is associated
Derived Attribute
An attribute whose values can be calculated from related attribute values
Strong Entity Type
An entity that exists independently of other entity types
Associative Entity
An entity type that associates the instances of one or more entity types and contains attributes that are peculiar to the relationship between those entity instances
Weak Entity Type
An entity type whose existence depends on some other entity type
Composite Identifier
An identifier that consists of a composite attribute
False
T/F A Cardinality constraint tells what kinds of properties are associated with an entity
True
T/F A business rule is a statement that defines or constrains some aspect of the business
True
T/F A good data definition is always accompanied by diagrams, such as the entity-relationship diagram
True
T/F A single occurrence of an entity is called an entity instance
False
T/F A ternary relationship is equivalent to three binary relationships
True
T/F An attribute whose values can be calculated from related attribute values is called a derived attribute.
True
T/F An entity is a person, place, object, event, or concept in the user environment about which the organization wishes to maintain data
True
T/F Data modeling is about documenting rules and policies of an organization that govern data.
False
T/F In an E-R diagram, strong entities are represented by double-walled rectangles
False
T/F Most systems developers believe that dat modeling is the least important part of the systems development process.
True
T/F One reason to use an associative entity is if the associative entity has one or more attributes in addition to the identifier
True
T/F The relationship between a weak entity type and its owner is an identifying relationship.
True
T/F When choosing an identifier, choose one that will not change its value often
True
T/F Τhe E-R model is used to construct a conceptual model
Identifying Owner
The entity type on which the weak entity type depends.
Maximum Cardinality
The maximum number of instances of one entity that may be associated with each instance of another entity.
Minimum Cardinality
The minimum number of instances of one entity that may be associated with each instance of another entity
Degree
The number of entity types that participate in a relationship
Identifying Relationship
The relationship between a weak entity type and its owner