Module 2: Database Architecture, Models and Diagram Flashcards
A Good Data Name 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
word or phrase with specific meaning
Term
association between two or more terms
Fact
Guidelines for Good Data Definition
- A concise description of essential data meaning
- Gathered in conjunction with systems requirements
- Accompanied by diagrams
- Achieved by consensus, and iteratively
person, place, object, event, concept (often corresponds to a row in a table)
Entity Instance
collection of entities (often corresponds to a table)
Entity Type
link between entities (corresponds to primary key-foreign key equivalences in related tables)
Relationship Instance
category of relationship… link between entity types
Relationship Type
properties or characteristics of an entity or relationship type (often corresponds to a field in a table)
Attributes
a special entity that is also a relationship
Associative
specify number of entity types involved
Relationship Degrees
specify how many of each entity type is allowed
Relationship Cardinalities
- are statements that define or constrain some aspect of the business
- are derived from policies, procedures, events, functions
Business Rules
Business rules assert _____.
business structure
Business rules are automated through _____.
DBMS software
A Good Business Rule
- declarative
- precise
- atomic
- consistent
- expressible
- distinct
- business-oriented
what, not how
Declarative
clear, agreed-upon meaning
Precise
one statement
Atomic
internally and externally
Consistent
structured, natural language
Expressible
non-redundant
Distinct
understood by business people
Business-oriented
a person, a place, an object, an event, or a concept in the user environment about which the organization wishes to maintain data
Entity
a collection of entities that share common properties or characteristics
Entity Type
a single occurence of an entity type
Entity Instance
- exists independently of other types of entities
- has its own unique identifier
Strong Entity
Strong entity has its own unique identifier underline with _____.
single line
- dependent on a strong entity (identifying owner)… cannot exist on its own
- does not have a unique identifier (only a partial identifier)
Weak Entity
Weak entity box and partial identifier have _____.
double lines
Identifier is also primary called _____/
Primary Key
links strong entities to weak entities
Identifying Relationship
property or characteristic of an entity or relationship type
Attribute
Classification of Attrubutes
- Required vs Optional Attributes
- Simple vs Composite Attribute
- Single-Valued vs Multivalued Attribute
- Stored vs Derived Attributes
- Identifier Attributes
must have a value for every entity (or relationship) instance with which it is associated
Required
may not have a value for every entity (or relationship) instance with which it is associated
Optional
an attribute that has meaningful component parts (attributes)
Composite Attribute
may take on more than one value for a given entity (or relationship) instance
Multivalued
values can be calculated from related attribute values (not physically stored in the database)
Derived
is saved into the database
Multivalued Attributes
is not saved into the database because its values may change over time
Derived Attributes
an attribute (or combination of attributes) that uniquely identifies individual instances of an entity type
Identifier (Key)
an attribute that could be a key… satisfies the requirements for being an identifier
Candidate Identifier
one attribute only
Simple Identifier
two or more identifier attributes
Composite Identifier
Standard Format for Naming Attributes
[Entity type name {]Qualifier]}] Class
is modeled as lines between entity types
Relationship Type
two entities can have more than one type of relationship between them
Multiple Relationships
combination of relationship and entity
Associative Entity
the instance is between specific entity instances
Relationship Instance
is the number of entity types that participate in it
Degree of a Relationship
one entity related to another of the same entity type
Unary
entities of two different types related to each other
Binary
entities of three different types related to each other
Ternary
each entity in the relationship will have exactly one related entity
One-to-One
an entity on one side of the relationship can have many related entities, but an entity on the other side will have a maximum of one related entity
One-to-Many
entities on both sides of the relationship can have many related entities on the other side
Many-to-Many
can have attributes of its own
A Relationship
the number of instances of one entity that can or must be associated with each instance of another entity
Cardinality Constraints
Minimum cardinality if zero
Optional
Minimum cardinality if one or more
Mandatory
Maximum cardinality
the maximum number
- an entity that has attributes
- a relationship that link entities together
Associative Entities
is like a relationship with an attribute, but it is also considered to be an entity in its own right
Associative Entity
a time value that is associated with a data value, often indicating when some event occurred that affected the data value
Time Stamp
