Ch.5 MIS 3320

What are: atomic, composite, and derived attributes?

*atomic- every attribute are atomic (salary, Job title) composite - you do not want - attribute made up of more than one piece of information (name, address) derived- you do not want- one that is the result of a calculation typically , or a comparison (age bc it is derived by DOB, TotalPay) , want to store the source data

What does a relationship represent in an ERD?

- an association between entities - represents a "NEED TO KNOW the relationship" between the instances of each entity - occurs in two directions read it left to right- A department employs ___ employees read it right to left An Employee is employed by ___ department A = always talk about one instance

Know how to model an Order!!! - it will typically contain 3 entities

A business object is not always = 1 Entity.It may require more Step 1: Determine the initial entities• Step 2: Add the initial attributes that you are aware of.• Step 3: Identify/add a primary key• Step 4: Add the initial relationships• Step 5: Add the cardinalities

Know the ERD Rules & Tips.

An entity's name should represent one instance/record in the table! An entity with only one instance should not be modeled

Know the Types of Relationships: one to one, one to many, many to many. What determines the relationship type?

Maximum: • one, many Minimum: • zero - optional(don't have to have)(most of the time 0), one - mandatory

Why did we talk about "Things" in our system?

Nouns - "Things"• Roles - customer, supplier, doctor• Locations - warehouse, office, store• Organizational units - department, division, group• Events - order, payment, complaints, appointment• Tangible things - car, book, computer• Data collecting devices - thermostat, scanner, sensor

Entity nouns

Roles - customer, supplier, doctor • Locations - warehouse, office, store • Organizational units - department, division, group • Events - order, payment, complaints, appointment • Tangible things - car, book, computer • Data collecting devices - thermostat, scanner, sensor

What are attributes?

a characteristic about an entity - within scope -that we need to remember

What is an ERD? Know the various ERD symbols/notation

a data modeling technique

What is an entity?

a noun( a person, place, object, thing) that is : within our scope and that we need to remember (need to store, data base)

Are instances represented via a symbol on an ERD diagram? What will an instance eventually be in implementation?

a record a table in a data base only add an entity to your ERD if it has multiple instances

What will an entity eventually be in implementation?

a table in our data base

What is a primary key?

an attribute (or group of attributes) that uniquely identifies an instance each entity must have a primary key unique- no duplicate values required- cannot be null (empty) statistic- doesn't change

What is an instance?

an occurrence of our entity -record - ex: student entity:___ instance product entity:__instance if you have 1000 products you have 1000 instances

Who initially designs the ERD in the analysis phase? How will this be used in the design phase?

analysis- is used by the BA/SA to annalist in design - it is used by DBA to design

What are the issues concerning composite and derived attributes?

composite- more than one (name, address) derive- calculation( total pay, age)

What is the significance of nouns & verbs in data modeling & process modeling?

entity - is a noun relationship - verbs between entities

data base

is a collect of related tables

What is meant by cardinality? Be able to identify the correct minimum & maximum cardinalities.

maximum- given an instance in one entity, what is the maximum number of related instances in the related entity?(always pushed up next to entity) minimum- can an instance in one entity exist without a related instance in the related entity? (i.e. not eventually but now)

Know how to resolve a Multi-valued Attribute.

remove it make a new entity

What is a surrogate key? candidate key?

surrogate key- an auto-generated integer defined as the Primary Key. (student ID) candidate key- Multiple unique attributes may exist; if so, pick the attribute that is used most often and define it as the primary key

Know the Degrees of Relationships: unary, binary, ternary, n-ary.

unary- (recursive) (relationship self) - referencing entity ↳ a department at a University has a relationship with another department - they are the same type of entity ternary- contains 3 entities ↳ a student is registering for a course and section binary- relationship between 2 entities ↳ student registers for class n-ary- between 3+ entities modeling historical data: make sure to name specific dates and have all necessary attributes

What are the characteristics of a good primary key?

unique - no duplicate values (employee ID) Required - cannot be empty Static - does not change (e.g. build name - poor PK) should not change over time