Database Chapter 4: Database Modeling

attributes

describes the entities characteristics

entity instance

the occurrence of a particular entity

Identifying relationship

links strong entities to weak entities (if weak is ID-dependant, parent entity will be a composite primary key) -represented by a solid line

Data Modeling Process #5: Refine the Data Model

-Consider optionality -Consider cascading / restricted updates / deletions -Review alterations with the client -and finally obtain formal approval from client

Data Modeling Process #4: Define the Attributes

-Create domains -Identify indexes -Create column headings, default values, etc .-Create validation rules -Review the model with the client

Different sources of requirements:

-user interviews -forms -reports -queries -application programs -websites -use cases -business rules

ID- dependent weak entity

A weak entity that cannot exist without its parent entity. -has a composite identifier -first part is the identifier for strong entity -second part is the identifier for weak entity itself

minimum cardinality

the min number of entity instances that must participate in a relationship -typically assume value 0 (optional) or 1 (mandatory)

Data Modeling Process #1: Buisl a List of Entities

-Identify potential entities -Define possible unique identifiers -Define obvious non-key attributes

strong entity

An entity that is existence-independent, that is, it can exist apart from all of its related entities

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. -is used whenever a pure N:M relationship cannot properly hold attributes that are describing aspects of the relationship between two entities - a new entity is created to link 2 original entities and hold the attributes

weak entity

An entity type whose existence depends on some other entity type.

relationships

entities are associated with one another

identifier

an attribute (or group of attributes) whose value is associated with one and only one entity instance -SocialSecurityNumber, StudentID

Subtype Entity

an entity that represents a special case of another entity, called a supertype

prototyping

commonly use to validate forms and reports

Unified Modeling Language (UML)

is a set of structures and techniques for modeling and designing object-oriented programs (OOP) and applications.

If the identifier is unique, the data value..

must be unique for all instances

non identifying relationship

relationship between the strong and weak entity(is weak is (non-id-dependent, identifier of parent entity will be a foreign key) -represented by a dashed line -also used between strong entities

Exclusive subtypes

the supertype relates to at most one subtype

Data Modeling Process #2: Determine Relationships

-Determine cardinalities -Determine relationship types (e.g., associative)

Data Modeling Process #3: Draw Initial Data Model

-Formally define entities and relationships -Review the model with the client

one-to-one relationship (1:1)

between two entities in which an instance of one entity can be related to only one instance of a related entity

many-to-many relationship (M:N)

between two entities in which an instance of one entity is related to many instances of another and one instance of the other can be related to many instances of the first entity

has-a relationship

The relationship demonstrated by a class that contains another class. -an employee has a badge -a badge has an employee

cardinality

count of entity instances in a relationship

An attribute has a..

data type (character, numeric, date, currency) and properties determined from the requirements

degree

number of entity classes in the relationship -degree 2 = binary -3=ternary

maximum cardinality

the maximum number of entity instance that can be involved in a relationship -one, many or some other fixed number

composite

an identifier that consists of 2 or more attributes -(EmployeeNumber and LineItemNumber both required)

Entity Class

a collection of entities and provides the structure of the entities in that class

Three stages of database development:

-Requirements Analysis Stage -Component Design Stage -Implementation Stage -part of 5 stage system development life cycle model

supertype

A generic entity type that has a relationship with one or more subtypes, called a discriminator

recursive relationship

A relationship found within a single entity type. For example, an EMPLOYEE is married to an EMPLOYEE or a PART is a component of another PART.

Integrated Definition 1, Extended (IDEF1X)

A version of the entity-relationship model, adopted as a national standard, but difficult to understand and use. Most organizations use a simpler E-R version like the crow's foot model

one-to-many relationship (1:N)

Relationships involving two entity types in which an instance of one type can relate to many instances of the second type, but an instance of the second type can relate to at most one instance of the first

Information Engineering (IE)

[James Martin 1990] It uses "crow's feet" to show the many sides of a relationship, and is sometimes called the crow's foot model.

inclusive subtype

a supertype instance can relate to one or more subtypes

Business Rules

may constrain the data values and the processing of the database: -Heather Sweeney Design has a business rule that no more than one form letter or email per day is to be sent to a customer•

IS-A relationship

relationship that connected super type and subtypes, because subtype is the same entity as the super type