ITM 310: Chapter 2

An attribute that cannot be broken down into smaller components that are meaningful to the organization.

Simple (or Atomic) Attribute

A simultaneous relationship among the instances of three entity types. All 3 entities must be set up and exist at the same time.

Ternary Relationship

*Declarative-what, not how *Precise-clear, agreed-upon meaning *Atomic-one statement *Consistent-internally and externally *Expressible-structured, natural language *Distinct-non-redundant *Business-oriented-understood by business people

A Good Business Rule Is:

-Related to Business, NOT Technical, Characteristics. -Meaningful and Self-Documenting -Unique -Readable -Composed of words from an approved list. -Repeatable -Written in Standard Syntax

A Good Data Name Is:

What is a derived attribute, and how is it different from a stored attribute?

A derived attribute is an attribute whose value can be calculated from other related attributes. A derived attribute is not stored in the physical table which is eventually created from the ERD. A stored attribute, as its name implies, is stored as a column in the physical table.

How is a strong entity different from a weak entity?

A strong entity type exists independently of any other entities. A weak entity type depends on another (strong) entity type. When an instance of the strong entity type no longer exists, any weak entity instances which depend upon the strong entity cease to exist.

What is an associative entity?

An associative entity is 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. A many-to-many relationship is converted to an 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. *A special entity that is also a relationship.

Associative Entity

A person's name, birthday, and social security number are all examples of:

Attributes

Properties or characteristics of an entity or relationship type (often corresponds to a field in a table).

Attributes

Most popular. Two entities linked together. A relationship between the instances of two entity types.

Binary Relationship

A 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. -Are statements that define or constrain some aspect of the business. -Are derived from policies, procedures, events, functions. -Assert business structure. -Control/influence business behavior. -Are expressed in terms familiar to end users. -Are automated through DBMS software.

Business Rules

A ________ specifies the number of instances of one entity that can be associated with each instance of another entity.

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.

Cardinality Constraint

Formulated by one or more attributes to have a full meaning. Ex: Telephone Number, Address, Course Information

Composite Attribute

An identifier that consists of a composite attribute.

Composite Identifier

Data modeling may be the most important part of the systems development process because:

Data characteristics are important in the design of programs and other systems components.

What are some of the guidelines for good data names of objects in general?

Data names always should: 1. Relate to the business, not technical characteristics. Student would be a good name but not filest023 2. Be meaningful so that the name tells what the object is about 3. Be unique 4. Be readable 5. Be composed of words taken from an approved list 6. Be repeatable 7. Follow a standard syntax

The number of entity types that participate in a relationship is called the:

Degree

The number of entity types that participate in a relationship.

Degree

Age- Not good because it changes every year. An attribute whose values can be calculated from related attribute values.

Derived Attribute

Customers, cars, and parts are examples of:

Entities

Person, place, object, event, concept (often corresponds to a row in a table).

Entity

A single occurrence of an entity type.

Entity Instance

A collection of entities that share common properties or characteristics

Entity Type

A graphical representation of an entity-relationship model.

Entity-Relationship Diagram (ER Diagram)

A logical representation of the data for an organization or for a business area.

Entity-Relationship Model (ER Model)

An attribute (or combination of attributes) whose value distinguishes instances of an entity type.

Identifier

Primary Key

Identifier Attribute

The entity type on which the weak entity type depends.

Identifying Owner

The relationship between a weak entity type and its owner.

Identifying Relationship

Business policies and rules govern all of the following EXCEPT:

Managing Employees.

A student can attend five classes, each with a different professor. Each professor has 30 students. The relationship of students to professors is a ________ relationship.

Many-to-Many

The maximum number of instances of one entity that may be associated with each instance of another entity.

Maximum Cardinality

The minimum number of instances of one entity that may be associated with each instance of another entity.

Minimum Cardinality

All different values or even more than one value. An attribute that may take on more than one value for a given entity (or relationship) instance. O Ex: Employee and Skills

Multivalued Attribute

The number of entity types that participate in a Unary relationship is:

One

Has a value or not. An attribute that may not have a value for every entity (or relationship) instance with which it is associated. *Not=NULL: WITHOUT value

Optional Attribute

Foreign Key

Partial Identifier Attribute

A meaningful association between (or among) entity types.

Relationship Type

Link between entities (corresponds to primary key-foreign key equivalencies in related tables).

Relationships

An attribute that must have a value for every entity (or relationship) instance is a(n):

Required Attribute

An entity that exists independently of other entity types. Stand on its own Ex: Employee

Strong Entity

An entity that exists independently of other entity types.

Strong Entity Type

What are the three different degrees of relationship?

The three possible degrees are: Unary (an instance of one entity is related to an instance of the same entity type), Binary (an entity instance of one type is related to an entity instance of another type), and Ternary (instance of three different types participate in a relationship).

A single occurrence of an entity is called an entity instance. T/F

True

An entity type name should always be a singular noun.

True

When choosing an identifier, choose one that will not change its value often. T/F

True

In an E-R diagram, there are/is ________ business rule(s) for every relationship.

Two

Record has relationship with itself. A relationship between instances of a single entity type.

Unary Relationship

An entity type whose existence depends on another entity type is called a ________ entity.

Weak

Does not exist unless the strong entity exists. DEPENDENT

Weak Entity