1. DB Implementation: MS Access Tables

2. RDB Implementation: Overview
Tables
Translation of ER model in RDBMS construct
For data storage
entities, attributes, relationships
Forms
Data input/display user interface
e.g. data entry form, search form
For viewing, editing, entering, dynamic querying
Queries
Relational algebra operations
combination of join, select, sort, filter, modify, etc.
For data retrieval & manipulation
Reports
Data display output
e.g. monthly reports (set query results)
Forms can manipulate data, but reports cannot
Database Design

3. RDB Implementation: Table
Table is the fundamental element in a relational database.
Contains data about a particular subject
row = record = an entity (e.g., an employee, a product)
column = field = an attribute (e.g., last name, product description)
Users seldom see tables if at all.
Data entry is usually done via forms.
Main issues in table design
What are the key attributes?
i.e., primary & foreign keys
What is the data type for each attribute?
e.g. text, number, date, etc.
What are the properties for each attribute?
e.g. size, input/output format, range, etc.
Database Design

4. MS Access Table: Data Types
Text
Alphanumeric data up to 255 characters.
Memo
Alphanumeric data with more than 255 characters
Used for notes or comments: Cannot search or index on memo data type fields
Number
Numeric data for fields that need to have computational operations done
AutoNumber
Unique values created by Access for each new record (sequential number)
→ Cannot be changed once created
Date/Time
Dates and Time values for the years 100 through 9999.
Currency
Monetary values
Yes/No
Boolean (true/false, Yes/No, On/Off) → good for checkbox type field
Hyperlink
Links that opens a file or a Web address (e.g. URL, address)
Attachment
Any supported files to attach (image, spreadsheet, document, chart, etc.)
Lookup Wizard
Tool to create lookup fields (i.e., dropdown list)
Displays values derived from existing table/query or a manually specified list
Calculated Field
Results of a calculation (must be based on fields in the same table)
MS Access 2010: Data Types & Field Properties
Database Design

5. MS Access Table: Field Properties
Field Size
To set the maximum size for data type (e.g., Text, Number)
Affects the stored value (via rounding, truncation) & DB size
Format
To customize the display/print layout of data
Does not affect the stored value (e.g. Currency  $1,234.50)
Input Mask
To set the data input template to guide data entry
e.g. Short Date  MM/DD/YYYY  99/99/0000;0;_
Validation Rule
To validate/restrict data entry
Use with Validation Text to display message on validation failure
An expression that specify valid data values
Database Design
MS Access 2007: Field Properties Quick Reference

6. MS Access: Lookup Field
Lookup Field/Column
Displays a list of choices in a combo box or list box.
The list is retrieved from another table/query or a value list.
Creating a Lookup field via Lookup Wizard
Select Lookup Wizard in Data Type column.
The Lookup Wizard starts
Select the Data Source in Lookup Wizard
Look up the values in a table or a query, or Type in the values.
For Table/Query-based lookup field,
Choose a table/query
Select fields (visible + data store)
For Value List-based lookup field,
Enter the number of columns to include in the lookup field.
Type the values in the grid
Choose the field whose value will be used
List Box
Combo Box
Database Design
MS Access 2007: Lookup Field

7. MS Access: Referential Integrity
Necessary Conditions
Matching field from “one” side of related tables
Must be a primary key or have the Indexed property set to “Yes (No Duplicates)”.
Related fields must have the same data type.
exception: AutoNumber to Number when both have the same Field Size
Effects
Cannot enter a value in the foreign key field that does not exist in the primary key of the primary table
Cannot delete a record in the primary table if matching records exists in the related table
Cannot change a primary key value in the primary table if that record has related records.
Cascading Updates/Deletes
Allows automatic updates/deletes of all related records along with primary record
e.g. change in primary key value in the primary table will be reflected in foreign key value of the related table
Enabled/disabled in the relationships window
Database Design

8. Table How-To: Overview
Create a table.
Table Design in Create tab
Add fields to the table
Data Type
Field Properties
Set the primary key
Select the PK field
Click the Primary Key icon (Design tab)
Save & name the table
Set the Relationships (Database Tools tab)
Database Design

9. Table How-To: Creation
Create a table in a new database
Click the File tab, and then click New.
In the File Name box, type a file name for the new database.
To browse to a different location to save the database, click the folder icon.
Click Create.
A new database opens, and a new table named Table1 is created and opens in Datasheet View.
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3.b
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1.b
Database Design

10. Table How-To: Creation
Create a table in an existing database
Click the File tab, and then click Open.
In the Open dialog box, select the database that you want to open, and then click Open
On the Create tab, in the Tables group, click Table Design
A new table is inserted in the database and the table opens in Design view
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Database Design

11. Table How-To: Fields Add a field to an existing table
Open a table in Design View.
Type a name for the field in the Field Name column.
Select an appropriate data type in the adjacent Data Type column.
Text, Memo, Number, Date/Time, Yes/No, etc.
Set Field Properties.
Field Size, Format, Input Mask, Validation Rule, etc.
Lookup Wizard
Field Properties
Database Design

12. Table How-To: Primary Key
Set a table's Primary Key
Select the table whose primary key you want to set or change.
On the Home tab, in the Views group, click View, and then click Design View.
In the table design grid, select the field or fields that you want to use as the primary key.
To select one field, click the row selector for the field that you want
To select more than one field, hold down CTRL, and then click the row selector for each field
On the Design tab, in the Tools group, click Primary Key.
A key indicator appears to the left of the field or fields that you specify as the primary key
To add an Autonumber primary key
In the Field Name column of an empty row, type a name (e.g., CustomerID)
In the Data Type column, click the drop-down arrow and click AutoNumber.
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2.b
Database Design

13. Table How-To: Relationships
Click Relationships in the Database Tools tab.
Click Show Table in the Design tab.
Select tables and then click Add. When finished, click Close.
Drag the Primary Key from one table to the Foreign Key in the other table.
To drag multiple fields, press the CTRL key, click each field, and then drag them.
Verify that the field names shown in the Edit Relationships dialog box are correct.
If a field name is incorrect, click the field name and select a new field from the list.
Select the Enforce Referential Integrity check box.
Click Create.
Database Design

14. MS Access Field Properties
Field Size
Format
Input Mask
Validation Rule
Database Design

15. Field Property: Field Size
Text Data Type
1 to 255
Number Data Type
Determines the precision of the number that can be stored
precision = number of significant digits
Autonumber is 4 byte
Setting
Storage Value (Min, Max)
Significant Digits
Storage Size
Byte
(0, 255)
N/A
1 byte
Integer
(-32,768, 32,767)
2 bytes
Long Integer
(–2,147,483,648, –2,147,483,647)
4 bytes
Single
(–3.4*1038, +3.4*1038)  7
Double
(–1.797*10308, 1.797*10308)  15
8 bytes
Decimal
(-9.999*1027 , 9.999*1027) 28
12 bytes
Database Design

16. Field Property: Text Format
Symbol
Description
Example @
Required character (including space)
abc  ( abc)
&
Optional character
(&&&&&): abc  (abc)
<
Force all characters to lowercase.
ABC  (abc)
>
Force all characters to uppercase.
abc  (ABC)
[color]
Display the field’s content in the named color
abc  (ABC) \
Display next character as entered.
&\!: abc  abc!
“text”
Display the text btw. quotes.
&“ kg”: 16  16 kg *
Fill all blank spaces with the next character.
&*?: five  five???? (display length=8) !
Fill from left instead of right.
!*?: five  ????five (display length=8)
Determines how to display the contents of data in tables
does not affect the stored value
For enhancing readability
e.g., credit card/phone number 
Syntax
format for non-empty text; format for empty text
 display data as is, or ‘None’ when empty
Database Design
MS Access 2007: Format for Text & Memo Data Types

17. Field Property: Number Format
Symbol
Description
Example
Display a digit or 0.
00,000:  01,234 #
Display a digit or nothing.
##,###:  1,234 %
Multiply by 100 and append % sign
##.#%:  12.3%
Section
Description
First
Format for positive numbers
Second
Format for negative numbers
Third
Format for zero values
Fourth
Format for Null values
Pre-defined formats
Currency e.g. displays ‘ ’ as ‘$1,234.56’
Percent e.g. displays ‘ ’ as ‘ %’ (requires size = “double”)
Scientific e.g. displays ‘ ’ as ‘1.23E+3’
Examples
0;(0);;”Null”
display positive numbers normally, negative numbers in parenthesis, “Null” if the value is null
Database Design
MS Access 2007: Format for Number & Currency Data Types

18. Field Property: Date/Time Format
Symbol
Description d
Day of the month in one or two digits (1 to 31) dd
Day of the month in two digits (01 to 31)
ddd
First three letters of the weekday (Sun to Sat)
dddd
Fullname of the weekday (Sunday to Saturday)
m, mm, mmm, mmmm
Month equivalent to d, dd, ddd, dddd y
Number of the day in a year (1 to 366) yy
Last two digits of the year (01 to 99)
yyyy
Full year (0100 to 9999) w
Day of the week (1 to 7)
h/hh, n/nn, s/ss
Hours, Minutes, Seconds (1 digit/2 digit)
Pre-defined format
Description
Short/Medium/Long Date
e.g. 2/28/2003, 28-Feb-03, Friday, February 28, 2003
Short/Medium/Long Time
e.g. 13:00, 1:00 PM, 1:00:00 PM
General Date
Combination of Short date and Long Time as needed e.g. 2/28/2003 1:00:00 PM
Example: ddd", "mmm d", "yyyy  Fri, Feb 28, 2003
Database Design
MS Access 2007: Format for Date/Time Data Type

19. Field Property: Input Mask
Symbol
Description
Required digit (0 to 9) 9
Optional digit or space (0 to 9) L
Required letter ?
Optional letter A
Required letter or digit a
Optional letter or digit
&
Required character or space C
Optional character or space #
Required digit, space, or +/-
Password
Display entry with *
Section
Description
First
Specifies the input mask
Second
Specifies whether the data is stored with the literal display characters to include literal characters, 1 or blank to store typed characters only
Third
Specifies the display character for data input positions
Data input template
a set of literal and mask characters that control what can and cannot be entered in a field
to prevent invalid data entry
e.g. (999) ;;_
data entry: (___) ___-____  (812)
data storage:
area code is optional
e.g. >L<??????????????
A first of last name with the first letter automatically capitalized
Database Design
MS Access 2007: Input Mask

20. Field Property: Format vs. Input Mask
Input Mask property
To control how data is entered
Affects how data is displayed during data entry
Can affect how data is stored
Format property
To display data in a consistent format
Affects how data is displayed after it is saved
Does not affect how it is stored
Decimal Places property (for Number data type)
Specifies the number of decimal places to display
Must use Field Size property to change how a number is stored
Has no effect if Format property is blank or set to “General Number”
Database Design

21. Field Property: Validation Rule
Validates & Restricts data entry
Validation Text holds the error message to be displayed
Use “expression” to define validation rules
expression is a combination of operators, fields, functions, etc.
expression can be constructed using the Expression Builder
Other Data validation in MS Access
Data Type – e.g., Date/Time
Field Size – e.g., 20 char for last name
Required – e.g., Yes to require data entry
Input Masks – e.g., for zipcode
Examples
Validation Rule
Description
<> 0
Entry must be non-zero
>1000 Or Is Null
Entry must be greater than 1000 or blank
Like “A????”
Entry must be 5 characters and begin with the letter “A”
>= #1/1/96# And <#1/1/97#
Entry must be a date in 1996
Database Design
MS Access 2007: Validation Rule

22. Access Table: Misc. Field Properties
Indexed
create internal record of the field values for searching
Access updates all of its indexes every time a table record is added or updated
too many indexed fields can slow down data entry
Primary key field should be set to “Yes (No Duplicates)”
exception: set composite primary key fields to “Yes (Duplicates OK)”
Required
Yes/No to indicate whether the data entry is mandatory
Allow Zero Length
Yes/No to indicate whether a zero-length string (“”) is a valid entry
Caption
label for the field (default= field name)
Default Value
value automatically entered for new records
Unicode Compression
compresses Unicode character representation
2 bytes to 1 byte when the first byte is 0 (e.g. English)
IME Mode
set Input Method Editor Mode (e.g. Hangul)
Database Design
MS Access 2007: Field Properties Quick Reference

23. MS Access: Null vs. Zero-length string
A variable state indicating missing data
Information that may exist but is unknown
i.e., “I don’t know what the value is.”
e.g., CUS_FAXNUM is set to Null initially.
Created by pressing ENTER key in a field
Zero-length string
To handle unknown values in required fields
Information that does not exist
i.e., “I know there is no value.”
e.g., CUS_FAXNUM is set to zero-length string after discovering that the customer has no fax.
Created by entering two double quotes (“”) in a field
Database Design