MIS week 3
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- Created by: jmf00632
- Created on: 03-01-20 11:07
What is an informationn system?
An information system is a set of interrelated components that collect and process data to produce information.
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which means......
we need a way to store data
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how do we store data effectively and efficiently?
To store data efficiently and effectively in a database we need to model it.
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what 3 things consist of modelling data?
entities, attributes and relationships
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what is an entity?
o What “things” are the data about? - . its a category of things.
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what is an example of entities?
e.g. students name, ? People, objects, events, etc. e.g., employee, product, order
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entity is an......
abstract concept
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an example of an entity - student
first name surname date of birth address phone no
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instance is a....
concrete example of the concept
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Abstract
not physical
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concrete
physical
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FYI
LOOK IN BOOK FOR ABSTRATC/ CONCRETE
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What is an attribute?
What are the characteristics of the “things” ? e.g. address
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an attriribute is…..
a property of an entity
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attributes have....
values from specific instances
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an instance may have…..
missing values (null)
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there are 5 types of attributes - what are they?
single, composite, simple valued, multi, store versus derived
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simple
o A simple attribute cannot be broken down into a smaller component.
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composite
A smaller attribute can be divided into smaller components, which represent more basic attributes that have their own meanings
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single valued
Having only a single value of each attribute of an entity.
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multi valued
• Having the potential to contain more than one value for an attribute. • An entity in relational database cannot have multi-valued attributes. Those attributes must be handled by creating another entity to hold them
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store versus derived
• If an attribute can calculated using the value of another attribute, it is called a derived attribute. • The attribute that is used to derive the attribute is called a stored attribute.
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business rules intend to convey......
the behaviour and rules of a business
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for example in a book store.....
o A customer can purchase many books. o Books can be purchased by many customers. o A book title can have many copies.
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another example in terms of uni...
• for example a student needs access to slides, a timetable, • then the lecturer needs access to the students number • from this we can identify the entities and then the attributes- city, post code e,c,t,
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• One of the main reasons for creating an ERD is to ....
identify and represent the relationships between entities.
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what do entity relationship diagrams (ERD) do for the organisation?
ER diagram depicts the organisation of data with simple graphical symbols
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relationships - Entities are related in one way or another - this can through
cardinality relationships or Optionality of relationships
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cardianlity relationships.....
o One-to-One Relationships o One-to-Many Relationships o Many-to-Many Relationships
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o Many-to-Many Relationships – example
for example a lecture can be presented to may stidents at one time
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Optionality of relationships
o Mandatory o Optional
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Cardinality of Relationship - husband to wife
one to one
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Cardinality of Relationship - student to project
one to many
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Cardinality of Relationship - player to team
one to many
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Cardinality of Relationship- child to parent
one to one
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Cardinality of Relationship - stuent to module
one to many
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why do we need ERD (ENTITY REL DIAGRAMS)
Its the first step to build a database
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so what is a database?
A bunch of logically related tables (R-tables) with data
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why do we need databases?
Each entity corresponds to exactly one table in a database
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what are the 6 challenges of managing data?
data redundancy, data inconsistency, data quality, lack of flexibility, poor security, lack of data sharing and availability
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data redundancy
the same data stored in many places
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data base solution - how can we solve these issues?
logically integrating and linking all the tables
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by logically integrating and linking all the tables we achieve,,,, (5)
• Centralised and integrated data storage • Minimal data redundancy • Limited inconsistency • Service of multiple applications • Enforcement of data standards, access rules, integrity constraints and security
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what do we need befroe we link the tables?
we need keys
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what does a primary key do?
A “primary key” (PK) uniquely identifies a record
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an example.......
–e.g., emplID in the Employee table
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what is a foreign key?
a foreign key is a primary key in another table - not neccasirily uniwue in this table
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what is database normalisation?
Normalisation is the process of eliminating data redundancy and ensuring data integrity
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what is data redundancy?
• Duplicate records in a table • Same field in two different tables • Data can be derived from other fields (e.g., total price of an order)
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goals of normalisation
oSave space - store each piece of data only once oAvoid inconsistency - changing data once changes it everywhere oMore rapid updates
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Other cards in this set
Card 2
Front
which means......
Back
we need a way to store data
Card 3
Front
how do we store data effectively and efficiently?
Back
Card 4
Front
what 3 things consist of modelling data?
Back
Card 5
Front
what is an entity?
Back
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