Application Software: Databases

CHAPTERS 15-16

Databases

A database is a collection of dataDatabase software helps you find, organize,

update, and report information stored in a database

Database Concepts Database Management System Software is

used to create, maintain, and access information in an electronic database.

Common Database Management SystemsMicrosoft AccessBorland dBasemySQLOracle

Data Organization “Hierarchy”

Databases: a collection of files with the connections between them

Files : Information dealing with different types of data are stored in different files

(i.e. addresses, transcripts, and schedules)Records : Each instance in a file is called a record

(i.e. all information about one student)Fields : Each part of a record is called a field

(i.e. Zip Code for a student)

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Database Terminology Field Record Table Database

A database is made up of one or more tables

Individual tables in a database

Records

Individual fields

Tables in a Database

Each DB file has a table structure for its records.

The table structure is created first and given a table name as well as a set of fields.

Table Design Considerations

Just as you first create a blueprint to build a house, you should first sketch or outline the design of a database table

Careful pre-planning

will save you much time

in the future

Tables in a Database Each Field in the table has…

namedata type field width

After the table structure is complete, data can be entered into the table’s fields.

default valuesrequired?primary key?

Data Types for the Fields

Text alphanumeric, alpha, string – holds any character

Numeric byte, short, long, integer floating point (decimal) , currencies

Date Memo Logical (binary or boolean or yes/no) Hyperlink Object

Table Design Considerations – Field Size Property

Set the field size in Table Design View Always anticipate the current field size,

may one day need to be larger

Set field size in the Field Properties grid of Table Design View

Data Validation

Make sure the data in the computer matches the real-world information it representsData Type EnforcementDefault ValuesRangesRequired FieldsUnique KeysNon-Null Keys

Data Validation

Make a field numeric types ONLY when you plan to do arithmetic with the field and it makes sense to do it!

Social security numbers, for example, should be TEXT not Long integers – you do not want someone to total them by accident, it would be meaningless

Table Design Consideration – Sarbanes Oxley Act (SOX)

Protects the general public and companies shareholders against fraudulent practices and accounting errors. Requires that all business records be saved

for a period of five years and be made available to the SEC upon request

SOX RECORDS

Do Not

Discard

Table Design Considerations - PNPI

Short for Personal, Non-Public, Information PNPI laws govern the safeguarding of data such as:

social security numbers credit card numbers Educational records (FERPA) bank account numbers medical records (HPAA)

Table Design Considerations – Store Data in its Smallest part

For greater flexibility, store data in its smallest part Instead of one field for an address, use many Instead of one field for a name, two or three

Like this

Not like this

Table Design Consideration - Plan for Date Arithmetic

Using a data type of date/time for all date fields allows the use of date arithmetic

Fields declared as a data type of Date/Time

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Work with Table Views

Datasheet (Table) View – used to add, modify, delete and view records

Design View – used to create and modify the fields in a table

Datasheet View

Design View

Work with Properties

Field Properties can be used to specify characteristics for individual fields

Located in the lower pane of Table Design View

Caption property

Field Size property

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Objects

Tables Queries Reports Forms Macros Modules

Objects

Reports

Reports are created when a more formal printout is desired. Use a wizard to create a reportExecutes one or more queries and presents

the results in a more organized fashionCan sort the data, can do simple arithmetic

(totals)

Queries Queries are questions used to retrieve

information from a database. Contain criteria to specify the records and

fields to be included in the query results. Can contain wild cards or logical operators to

make more complex queries * and ? <, >, <=, >=, <>, =, AND, OR, etc…

Named and saved so they can be run again at a later time.

Query Languages A query language such as SQL (Structured

Query Language) provides a set of commands for locating and manipulating dataLIST ALL FOR STATE = “KY”Not user friendly

Query By Example is another query language Fill out a form that describes your queryMore friendly

Queries

Queries allow us to ask questions about data This record set that answers our question is called

a dataset

Employees table

Dataset resulting from querying table for only employees who are Sales Representatives

Using Query Design View

Query Design grid has two panes – the table pane and the design pane

Striking the F6 key will toggle you between sections

Tables pane

Design pane

Specifying Criteria in a Select Query

Field row – displays the field name Sort row – enables you to sort the dataset Show row – controls whether or not you see a

field in the dataset Criteria row – determines the records that will be

selected for display

Fields in design grid allow us to specify criteria for the dataset

Specifying Criteria – Currency and Operands

Specify criteria with currency Without the dollar sign With or without the decimal point

Use operands such as: Less than and greater than Equal to or not equal to

Greater than (>) operand

Currency amount entered without dollar sign

Specifying Criteria – Wildcards

Asterisk - searches for a pattern that includes any number of characters in the position of the asterisk

Question mark - searches for a pattern that includes a single character in the position of the question mark

Query with asterisk wildcard and resulting dataset

Query with question mark and asterisk wildcard and resulting dataset to specify criteria for the dataset

Specifying Criteria – And and Or

OR finds records that can match one or more conditions

AND finds records that must match all criteria specified

Or Criterion and resulting dataset

And criterion and resulting dataset

Run a Query

Running, or executing, a query is done by clicking the Run command

Run command

Add a Total Row in a Query

The total row can be added to the design grid by clicking the Totals Icon

Totals Icon

Total row added to the query

Calculated Queries

Will find averages, max, min, sum, std Work with ONE field – NOT more! Add Totals row to query Open “Group By” menu Choose appropriate function Run query

Sorting Records

Can sort records in a database by field values Single Field Sort

Sort all students in the DB by home state Multi-Field Sort (Field A within Field B)

Sort all students in the DB by home state then by alphabetical order of last name (Name within State) State is primary sort field, Name is secondary sort field

Access sorts multiple fields left to right

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Sorting Table Data

Lists records in ascending or descending order according to one or more fields

Last Name field sorted ascending

Last Name field sorted descending

Concurrent Processing Large databases allow more than one person to

access a file at one time Have to be careful to control access - can lose data

that way - who writes LAST? MS Access uses a .ldb file to control this .ldb file created when a mdb file is opened, says that it

is "locked" so no one else can use it .ldb file goes away when mdb file is closed DO NOT submit it INSTEAD of your mdb!

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Compact and Repair

Compact and Repair is located under the Manage menu

Fixes problems due to inefficient file storage and growth of a database Should be performed everyday Often decreases the file size by 50% or more

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Access or Excel?

You are working with large amounts of data

You need to create relationships between your data

Your data is of a manageable data size

There is no need for relationships between data

You are primarily creating calculations and statistics

Use Access when: Use Excel when:

Understand Large Database Differences Most large companies separate their

database into front and back ends Front end – contains the objects needed to

interact with data, but not the tables where the record values reside

Back end – contains the tables where the data resides

Data Mining – a question for society

the process of extracting hidden patterns from data (from Wikipedia)

Businesses and governments do it all the time (finding prospects, detecting terrorism)

For Knowledge Discovery and Prediction Privacy concerns – identifying specific

individuals