Database Management: Chapter 2 – Flashcards
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Entity-Relationship Model
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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
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Entity-Relationship Diagram
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Graphical representation of an entity-relationship model
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Business Rule
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Statement that defines or constrains some aspect of the business. It is intended to assert business structure or to control or influence the behavior of the business.
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Characteristics of a Good Business Rule
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Declarative, precise, atomic, consistent, expressible, distinct, business-oriented
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Data Name Guidelines
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Relate to business, not technical characteristics, are meaningful, are unique, are readable, are composed of words taken from an approved list, are repeatable, and follow a standard syntax
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Term
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Word or phrase that has a specific meaning for a the business
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Fact
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Association between two or more terms
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Entity
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Person, place, object, event, or concept in the user environment about which the organization wishes to maintain data
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Entity Type
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Collection of entities that share common properties or characteristics
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Entity Instance
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Single occurrence of an entity type
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Strong Entity Type
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Entity that exists independently of other entity types
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Weak Entity Type
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Entity type whose existence depends on some other entity type
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Identifying Owner
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Entity type on which the weak entity type depends
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Identifying Relationship
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Relationship between a weak entity type and its owner
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Attribute
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Property or characteristic of an entity or relationship type that is of interest to the organization
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Required Attribute
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Attribute that must have a value for every entity (or relationship) instance with which it is associated
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Composite Attribute
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Attribute that has meaningful component parts, or attributes (address)
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Simple (Atomic) Attribute
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Attribute that cannot be broken down into smaller components that are meaningful to the organization
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Multivalued Attribute
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Attribute that may take on more than on value of a given entity, or relationship, instance (skill)
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Derived Attribute
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Attribute whose values can be calculated from related attribute values
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Identifier
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Attribute (or combination of attributes) whose value distinguishes instances of an entity type
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Composite Identifier
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Identifier that consists of a composite attribute
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Relationship Type
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Meaningful association between or among entity types (line and verb that denotes relationship between entities)
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Relationship Instance
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Association between or among entity instances where each relationship instance associates exactly one entity instance from each participating entity type (lines that connect each employee to each course they have taken)
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Associative Entity
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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
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Degree
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Number of entity types that participate in a relationship
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Unary Relationship
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Relationship between instances of a single entity type (person is married to another person)
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Binary Relationship
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Relationship between the instances of two entity types
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Ternary Relationship
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Simultaneous relationship among the instances of three entity types
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Cardinality Constraint
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Rule that specifies the number of instances of one entity that can or must be associated with each instance of another entity
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Minimum Cardinality
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Minimum number of instances of one entity that may be associated with each instance of another entity
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Maximum Caridnality
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Maximum number of instances of one entity that may be associated with each instance of another entity
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Time Stamp
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Time value that is associated with a data value, often indicating when some event occurred that affected the data value (transaction time)
