This excerpt from "Microsoft Office Access 2007 Forms, Reports, and Queries" introduces several techniques that serve to either make data entry less of a chore, or to reduce or eliminate data entry errors (or both).

Chapter 3: Designing Forms for Efficient and Accurate Data Entry

In this chapter

• Preventing Errors by Validating Data
• Using Controls to Limit Data Entry Choices
• Case Study: Using an Option Group to Select the Shipper
• Entering Data with ActiveX Controls
• Collecting Form Data via Email
• From Here

Data entry is one of those tasks that I describe as "dangerous" because it's a chore that's both tedious and important. It's tedious because entering dozens or hundreds of records is no one's idea of fun. It's important because the data must be entered accurately; otherwise, any analysis of the data becomes at best misleading and at worst just plain wrong. The danger, then, lies in the fact that data entry is prone to errors but can't afford to have any.

As a forms designer, you can help to reduce this danger by setting up your forms so that data entry is both as efficient as possible and as accurate as possible. In some cases you can achieve both goals with a single technique. For example, asking someone to type a customer name manually is both slow and prone to misspellings. However, suppose you already have a Customers table with a CustomerName field. If you relate the current table with the Customers table (using, say, a common CustomerID field), Access adds the CustomerName field to the current form using a drop-down list that contains all the customers. This makes data entry more efficient (the users just select a name from the list instead of typing it) and more accurate (the users can't misspell the customer name).

This chapter introduces you to several techniques that serve to either make data entry less of a chore, or to reduce or eliminate data entry errors (or both).

Preventing Errors by Validating Data

If, as the cooks say, a recipe is only as good as its ingredients, a database is only as good as its data. Viewing, summarizing, and analyzing the data are meaningless if the table you're working with contains erroneous or improper data. For basic data errors (for example, entering the wrong date or transposing a number's digits), there's not a lot you can do other than exhorting yourself or the people who use your forms to enter data carefully. Fortunately, you have a bit more control when it comes to preventing improper data entry. By "improper," I mean data that falls in either of the following categories:

• Data that is the wrong type. For example, entering a text string in a cell that requires a number.

• Data that falls outside an allowable range. For example, entering 200 in a cell that requires a number between 1 and 100.

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Note - To stress the importance of data entry, consider the story told to me by computer book author Greg Perry. Greg used to work for a large Fortune 500 company, and he says that the company made its data entry clerks enter all data twice: One clerk would enter the data in a file and then, when finished, another clerk would enter the same data. Then a comparison would be run to find exceptions where data didn't match, and that would then be reconciled. The lesson, he says, is that to the company, accuracy was far less costly than paying its employees to do the same job twice.

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The next few sections show you several techniques that can help you reduce these types of errors.

Helping Users with Text Prompts

You can prevent improper entries to a certain extent by adding text that provides details on what is allowable inside a particular cell. You have two choices:

• Add status bar text. This is a string that appears in the Access status bar when users enter the field. You specify this text by opening the field's property sheet, displaying the Other tab, and then entering the string in the Status Bar Text property.

• Add a label. Place a Label control near the field and use it to enter text that describes the field's data requirements or shortcut keys. For example, if the field requires a date, the label might say Press Ctrl+; to enter today's date.

For example, Figure 3.1 shows the Mortgage Calculator form. Notice the labels added beside the Interest Rate and Term text boxes that specify to the users that they must enter the interest rate per annum and the term in years. Note, too, the status bar text that appears when the users enter the Interest Rate field.

Figure 3.1
Use form labels and status bar text to give the users text prompts about the data they must enter.

Preventing Errors with Data Validation Expressions

The problem with text prompts is they require other people to both read and act on the text. The better solution for preventing data entry errors is the Access data validation feature. With data validation, you create rules that specify exactly what kind of data can be entered and in what range that data can fall. You can also specify pop-up input messages that appear when a cell is selected, as well as error messages that appear when data is entered improperly.

Follow these steps to define the settings for a data validation rule:

1. Display the property sheet of the field to which you want to apply the data validation rule.

2. Click the Data tab.

3. Click inside the Validation Rule property.

4. Enter a formula that specifies the validation criteria. You can either enter the formula directly into the property box, or you can click the ellipsis (...) button and enter the formula using the Expression Builder.

5. If you want a dialog box to appear when the users enter invalid data, click inside the Validation Text property and then specify the message that appears.

6. Close the property sheet to apply the data validation rule.

For example, suppose you want the users to enter an interest rate. This quantity should be positive, of course, but it should also be less than 1. (That is, you want users to enter 6% as 0.06 instead of 6.) Figure 3.2 shows the property sheet for a field named InterestRate that meets these criteria by defining the following expression in the Validation Rule property:

>0 And <1

Figure 3.2
Use the Validation Rule property to enter a data validation expression for a field.

Figure 3.2 also shows a string in the Validation Text property. If the users enter invalid data (that is, any value for which the Validation Rule expression returns False), the Validation Text appears in a dialog box, as shown in Figure 3.3.

Figure 3.3
If the users enter invalid data in the field, Access displays a dialog box such as this one, which uses the string entered into the Validation Text property.

Using Input Masks for Consistent and Accurate Data Entry

One of the major headaches that database administrators have to deal with is data entered in an inconsistent way. For example, consider the following phone numbers:

(123)555-6783
(123) 555-6783
(123)5556783
123555-6783
1235556783

These sorts of inconsistencies might appear trivial, but they can cause all kinds of problems, from other users misreading the data to improper sorting to difficulties analyzing or querying the data. And it isn't just phone numbers that cause these kinds of problems. You also see them with Social Security numbers, ZIP codes, dates, times, account numbers, and more.

One way to avoid such inconsistencies is to add a label or status bar message that specifies the correct format to use. As with data validation, however, these prompts are not guaranteed to work every time (or even most of the time).

A better solution is to apply an input mask to the field. An input mask is a kind of template that shows the users how to enter the data and prevents them from entering incorrect characters (such as a letter where a number is required). For example, here's an input mask for a phone number:

(___)___-____

Each underscore (_) acts as a placeholder for (in this case) a digit, and the parentheses and dash appear automatically as the user enters the number.

Using the Input Mask Wizard

The easiest way to create an input mask is to use the Input Mask Wizard. Here are the steps to follow:

1. Display the property sheet of the field to which you want to apply the input data.

2. Click the Data tab.

3. Click inside the Input Mask property.

4. Click the ellipsis (...) button to start the Input Mask Wizard, shown in Figure 3.4.

   Figure 3.4
   Use the Input Mask Wizard to choose a predefined input mask or to create your own input mask.

5. In the Input Mask list, click the input mask you want (or that's close to what you want) and then click Next.

6. Use the Input Mask box to make changes to the mask (see "Creating a Custom Input Mask Expression," next, for the specifics of which symbols to use); use the Placeholder Character list to choose the character you want to appear in the input mask as a placeholder; click Next.

7. Click the option that matches how you want the field data stored in the table (click Next after you've made your choice):

   • With the Symbols in the Mask—Click this option if you want the extra symbols (such as the parentheses and dash in a phone number mask) stored along with the data.

   • Without the Symbols in the Mask—Click this option to store only the data.

8. Click Finish.

Creating a Custom Input Mask Expression

If your data doesn't fit any of the predefined input masks, you need to create a custom mask that suits your needs. You do this by creating an expression that consists of three kinds of characters:

• Data placeholders—These characters are replaced by the actual data typed by the users. The different placeholders specify the type of character the users must enter (such as a digit or letter) and whether the character is optional or required.

• Modifiers—These characters aren't displayed in the mask; instead, they're used to modify the mask in some way (such as converting all the entered characters to lowercase).

• Literals—These extra characters appear in the mask the same as you enter them in the expression. For example, you might use parentheses as literals to surround the area code portion of a phone number.

Table 3.1 lists the data placeholders you can use to build your input mask expressions.

Table 3.1 Data Placeholders to Use for Custom Input Masks

Table 3.2 lists the modifiers and literals you can use to build your input mask expressions.

Table 3.2 Modifiers and Literals to Use for Custom Input Masks

You can enter your input mask expressions directly into the Input Mask property, or you can modify a predefined input mask using the Input Mask Wizard.

For example, suppose your company uses account numbers that consist of four uppercase letters and four digits, with a dash (-) in between. Here's an input mask suitable for entering such numbers:

>aaaa\-0000

Note, too, that input masks can contain up to three sections separated by semicolons (;):

first;second;third

first—This section holds the input mask expression.

second—This optional section specifies whether Access stores the literals in the table when you enter data. Use 0 to include the literals; use 1 (or nothing) to store only the data.

third—This optional section specifies the placeholder character. The default is the underscore (_).

For example, here's an input mask for a ZIP code that stores the dash separator and displays dots (.) as placeholders:

00000\-3333;0;.