M2 Flashcards
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 equivalencies 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
specify how many of each entity type is allowed
Relationship cardinalities
specify number of entity types involved
Relationship degrees
Entities are represented by X
X go in the softboxes
Entity names are always X and X
softboxes
Entity names
singular
written in capital letters
are listed under entity names
Attributes
X are marked with an asterisk: “*”
X are marked with a circle: “o”
X are marked with a hash sign: “#”
Mandatory attributes
Optional attributes
Unique identifiers
Business Rules
- Are statements that X or X some aspect of the business
- Are X from policies, procedures, events, functions
- Assert X
- X business behavior
- Are expressed in terms X to end-users
- Are X through DBMS software
define,,, constrain
derived
business structure
Control/influence
automated
A good business rule is:
- X–what, not how
- X–clear, agreed-upon meaning
- X–one statement
- X–internally and externally
- X–structured, natural language
- X–non-redundant
- X–understood by business people
- 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 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 occurrence of an entity type
Entity instance –
property or characteristic of an entity or relationship type
Attribute
X entity
• exists X of other types of entities
• has its own X identifier
• identifier underlined with X line
Strong
independently
unique
single
X entity
• dependent on a X (identifying owner)…cannot exist on its own
• does not have a unique identifier (only a X)
• entity box and partial identifier have X lines
Weak
strong entity
partial identifier
double
links strong entities to weak entities
Identifying relationship
•
Naming Attributes
• Name should be a X noun or noun X
• Name should be X
• Name should follow a X
• e.g. [Entity type name { [ Qualifier ] } ] Class
• Similar attributes of different entity types should use the
X
singular,,, phrase
unique
standard format
same qualifiers and classes
