Database Management: Chapter 2

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