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Data & Networks - PowerPoint PPT Presentation

Data & Networks. Problem Solving with Computers. Data & Information. Data is facts and figures Information is presented data But, before we extract information from data … Data often needs to be organized. Questions & Queries. We often ask questions to obtain information

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Data & Networks

Problem Solving with Computers

• Data is facts and figures

• Information is presented data

• But, before we extract information from data …

• Data often needs to be organized

• We often ask questions to obtain information

• The data we receive is organized such that we can readily see it’s information content

• Database

• Data organized to facilitate information retrieval

• Query

• A question we ask of the database

• What data would you need to answer the following questions?

• What percentage of students at WCSU have at least a 3.0 GPA?

• How many students graduated for each of the past five years?

• An object is a “thing” we wish to work with, such as …

• Person

• Sales receipt

• Car

• Music CD

• Objects in a collection share common attributes with each other

• Example:

• Objects: Cars

• Attributes: Make, Model, Year, Color, Price, etc.

• Attributes yield a method for describing an object, but are not the final object description

• Problem

• Develop a set of six (6) attributes for describing college students

• Remember, the actual set of values for these attributes should be unique for each student

• Each object in a collection is represented by a record in a database

• Each attribute identified for the collection is represented by a one or more fields

Collection

• A database is a collection of records

Object

• To be useful, there should be a one-to-one correspondence between objects and records

Record

Database

• Therefore …

• A record is a model for an object

• A database is a model for a collection of objects

• A database can consist of one or more database files

• Databases are often stored as tables

• Each row in a table is a record

• Each column in a table is a field

• Each field has an associated datatype and perhaps a length

• Hmmm … almost sounds like fields are variables, eh?

Record

Tables

Used Cars

• Problem:

• Create a simple table design for college course sections

• Select attributes that will yield a unique record for each course section

• Work in pairs

• You have 15 minutes to complete this exercise

• Primary key

• One or fields that represent a unique set of data for each record

• How did you insure that each record was unique?

• Was there any duplicate data?

• Used to create and edit databases

• Examples:

• Microsoft Access

• Filemaker Pro

• Facilitates

• Creation of tables

• Data entry

• Data retrieval

Demo

• Associations between two tables

• Based on common field(s)

• Often used to reduce errors and/or duplication of data

Example:Car Dealership Database

• Tables

• Car Models

• Cars

Models

Cars

Example:Car Dealership Database

• Each car can be associated with one model

• Each model can be associated with many cars

• This is a one-to-many relationship

Models

1

Cars

n

Example:Car Dealership Database

• Sometimes, a record in one related file cannot exist without a record in another file

• Is that the case here?

• Can you imagine a situation where this was true?

Models

1

Cars

n

Example:Car Dealership Database

• A common field(s) is required to form the link between two related files

Models

Model ID

:

1

Cars

Model ID

:

n

Example:Car Dealership Database

Models

Cars

Do this for homework!

• A structured question “asked” of a database

• Examples:

• How many cars were sold in January?

• What cars were sold in January?

• Were any cars sold in March?

• What is the data type for each answer?