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Computer Science & Engineering 2111

Computer Science & Engineering 2111

Lecture 10Introduction to Database Management Systems

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Database Terms

– Data• A collection of numbers and text

– 273459368

– Information• Meaning derived from the data

– SSN: 273-45-9368

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What is a database?• A large collection of data stored in a well-defined structure

– You can think of a database as• An electronic filing system• A repository for large amounts of information

– Example of a paper database• Telephone book

• Examples of computer databases– Ohio State stores student information in a database– Insurance companies store policy holder information in a

database– Your employer stores your information in a database

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Database Software• How do I create a database?– Purchase the software

• We will use MS Access 2010, but there are many database software products– Oracle– Sybase– SQL Server

• How do I access information in the database?– Purchase a Database Management System (DBMS)

• A DBMS is a collection of programs that enable you to enter, organize, and select data in a database.– We will use MS Access 2010, but there are many database

management software products

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Tables - a list of data organized into fields and records Queries - question structures to sort, filter and select

specific information Forms - structures for screen views of data Reports - structures for written output of data Program Modules & Macros - program code to perform

specific actions

Access DBMS “objects”:

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What is a database Form?• Structures for screen view and input of information• Used to simplify viewing and inputting of information

Datasheet View Form View

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• Structures for viewing written output of information

What is a database Report?

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FileTablePrimary Key

Each Record is made up of 8 Fields Data Type/Field Type

Field Properties

A field, or combination of fields, which uniquely identifies a record in a database

Primary

Key

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How is a database Organized? (Hierarchy of Data in a database)

Table

Each Record is made up of 8 Fields

File

16 Records

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Defining Properties for each Field in a TableFor a person’s social security number use:• What field type?– Text, Number - Short Integer, Number- Long

Integer etc. • Should it be optional or required?• Does the value need to be within certain

limits or from a predefined list?• Is there a default value?• Would an input mask be appropriate

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How should you decide what information goes on which table?

• If a fact appears in more than one record of a table, then this fact should probably be defined in another table.– Example: Account number

• Each fact should change in only one place– Example: Address

• Calculations shouldn’t be part of the database– Example: Current Balance

• Select a Primary Key where applicable so you can relate your tables– Example: Account number

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• The design should be initially created schematically, and then the database should be created using the chosen database software

Steps when setting up a Database

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1. Decide what information you will store in the database

Research Papers databaseFirst Name Charge Amount

Last Name Charge Date

Address Payment Amount

City Payment Type

State Payment Date

Zip Code

Home Phone

This database is a very simplistic one. Most databases you create will be much more complex.

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2. Create the layout of the database

• What tables do you need in your database?• How will you set them up?– Divide Tables into Inseparable Fields•Address as 1 field – • 17 Main St. New York, New York 10002

•Address as 4 fields• Street Address - 17 Main St. • City - New York• State - New York • Zip code – 10002

• What will be the field properties of each field?• What will be the primary key for each table?

• A field, or a collection of fields, whose values uniquely identify each record in a table

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Research Papers DatabaseTable Name: Client Field Type Properties

Fields: Client ID Text 5 Characters long Primary Key

First Name Text 25 Characters long

Last Name Text 50 Characters long

Address Text 60 Characters long

City Text 25 Characters long

State Text 2 Characters long Default Value

Zip Code Text 5 Characters long

Home Phone Text 10 Characters long Input Mask

Table Name: Charges Field Type Properties

Fields: Client ID Text 5 Characters long

Charge Amount Currency None

Charge Date Date Input Mast

Table Name: Payments Field Type Properties

Fields: Client ID Text 5 Characters long

Payment Amount Currency None

Payment Type Text 2 Characters long

Payment Date Date Input Mask

Table Name: PaymentMethod Field Type Properties

Fields: MethodID Text 2 Characters long

MethodType Text 20 Characters long

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3. Create a relationship diagram to identify the table, relationships, primary keys and foreign keys

• We know the information we want to store, but how do we match a customer’s name to their charges and payments?

• We need a way to relate these two tables to extract useful information.• We can relate these two tables by matching the Client ID

• Foreign key• A field that defines the relationship between 2 tables• Must be a primary key (unique) in at least one of the tables• The field names on each table do not have to match as long as the information is

the same.• The related fields must be the same data type• number, text etc.

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Table Name:ClientPrimary Key:ClientID

Table Name:ChargesPrimary Key:None

Foreign Key:ClientIDOn Charges table

Foreign Key:ClientID On Payments table

Table Name:MethodTypesPrimary Key:MethodID

Foreign Key:PaymentType On Payments table

RELATIONSHIP DIAGRAM FOR RESEARCH PAPERS DATABASE

1 1

1

∞

∞

∞Table Name:PaymentsPrimary Key:None

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4. Create the database using the database software

• Create tables– Fields– Primary keys– Field Types– Field Properties

• Create Relationships– “Join” tables– Enforce Referential Data Integrity

• A set of rules that specifies what records may exist in each table– A record input with a foreign key must always have a matching record in the primary key

table in the relationship

• Cascade Delete Related Records– Removing any entry in a primary key field will automatically remove all entries in foreign key

fields of related tables.

• Cascade Update Related Records– Updating any entry in a primary key field will automatically update all entries in foreign key

fields of related tables.

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ENFORCING REFERENTIAL DATA INTEGERITYCASCADE UPDATE & CASCADE DELETE

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Once Relationships are established you can gather information from one or more tables to answer questions

• Create a list of account numbers and owner names and total transactions

• What are the total deposits made by accounts starting with 5?

• What is the total balance of all accounts held by Jane Doe ?

These requests are known as Queries