MIS 235 Test 1

• Abstract representation of the date and the associations between them
• Entity Relationship Model is the most common

Also known as table, simple 2D grid of data made of: attributes, fields, columns

• a non null attribute of set of sttributes that uniqely identifies each instance/row of an entity
• every entity should have a primary key

simple is one word while composite is more than one word

• attribute(s) for a child instance/row of an entity that identifies the unique parent instance/row
• parents can be in the same or different entity from the child
• can be null under certain conditions (orphans) 
• typically the foreign key of a child identifies parent primary key

standardized set of notations for representing entities atrributes, primary keys, foreign keys and relationships between them

• unary- one entity
• binary-two entities
• n-ary- n entities

number of records (min and max) in each entity Y that can be associated with each record in X

• 1:N
• parent child, each Y with one X 
• put foreign key in the child that can be associated with each record in X the parent

• 1:1
• spouse relationship
• put FK in Y to identify X AND define a unique index to eliminate copies

• M:N
• siblings table
• create a new associative entity with 2 foreign keys to the associated records in X and Y

convert many to many relationship into a new entity consisting of two FKs to the associated records in X and Y

• actual/possibe
• associative entity works well with low density

Create a new associaive entity or super bridge w/ N foreign keys to point to the N sides of the relationships

process of eliminated redundant and inter dep0endent date from a database in order to improve consistency, maintainability, storage, efficiency and scalability

• duplicate data is eliminated
• pre calculated calues are eliminated
• fewer secondary indives per table

more tables, non intuitive, query complexity, slower queries

• multi value fields (comma deliminated, compud fields, list fields
• Repeating values
• compute field
• multilevel dependencies

• !NF-all data must be accessible by a primary key, each filed must be scalar (single value), no repeating columns
• 2NF-every non key field must depends on the entire PK
• 3NF- every non key field must depends only on the PK

primary key for every table

every non key field must depend on the entire PK

no compound values

• intentionally violating rules to improve performance
• only do when performance is ciritical

• Create
• Alter 
• Drop

defines new object

modify the definition of an existing object

throw away an object

• Select
• Inser
• Update
• Delete

answers quations, generates reports, etc

add new records

modify existing records

throw away records