Most people who use a computer in an office connect to others via a network. In fact, networks have also become common in homes. By enabling users to easily share data (and peripheral devices), networks make it much easier for people to work together on projects. Excel has a number of features that facilitate this type of cooperation, and those features are the subject of this chapter.
Note
If you’re working on a corporate network, you may need to consult with your network administrator before using any of the features described in this chapter.
A computer network consists of a group of PCs that are linked electronically. Users on a network can perform these tasks:
Access files on other systems
Share files with other users
Share resources, such as printers, scanners, and fax modems
Communicate with each other electronically
Excel has tools that enable you to work cooperatively with other Excel users on a project.
Networks provide users with the ability to share information stored on other computer systems. Sharing files on a network has two major advantages:
It eliminates the need to have multiple copies of the files stored locally on user PCs.
It ensures that the file is always up-to-date. For example, a group of users can work on a single document, as opposed to everyone working on his or her own document and then merging them all together.
Note
Some networks—generally known as client-server networks—designate specific computers as file servers. On these types of networks, the shared data files are normally stored on the file server. Excel doesn’t care whether you’re working on a client-server or a peer-to-peer network (where all the PCs have essentially equal functions).
Some software applications are multiuser applications. Most database software applications, for example, enable multiple users to work simultaneously on the same database files. One user may be updating customer records in the database, while another is extracting information for a report. But what if two users attempt to change a particular customer record at the same time? Multiuser database software contains record-locking safeguards that ensure that only one user at a time can modify a particular record.
Excel is not a multiuser application. When you open an Excel file, the entire file is loaded into memory. If the file is accessible to other users, you wouldn’t want someone else to change the stored copy of a file that you’ve opened. If Excel allowed you to open and change a file that someone else on a network had already opened, the following scenario could happen.
Assume that your company keeps its sales information in an Excel file that is stored on a network server. Esther wants to add this week’s data to the file, so she loads it from the server and begins adding new information. A few minutes later, Jim loads the file to correct some errors that he noticed last week. Esther finishes her work and saves the file. A while later, Jim finishes his corrections and saves the file. Jim’s file overwrites the copy that Esther saved, and her additions are gone.
This scenario can’t happen because Excel uses a concept known as file reservation. When Esther opens the sales workbook, she has the reservation for the file. When Jim tries to open the file, Excel informs him that Esther is using the file. If he insists on opening it, Excel opens the file as read-only. In other words, Jim can open the file, but he can’t save it under the same name. Figure 30.1 shows the message that Jim receives if he tries to open a file that is in use by someone else.
Jim has three choices:
Select Cancel, wait a while, and try again. He may call the person who has the file reservation and ask when the file will be available.
Select Read Only. This option lets him open the file to read it, but it doesn’t let him save changes to the same filename.
Select Notify, which opens the file as read-only. Excel pops up a message that notifies Jim when the person who has the file reservation is finished using the file.
Figure 30.2 shows the message that Jim receives when the file is available. If Jim opens the file as Read-Write, he receives another message if he makes any changes to his read-only version. He will have an opportunity to discard his changes or to save his file with a new name.
Although Excel isn’t a true multiuser application, it does support a feature known as shared workbooks, which enables multiple users to work on the same workbook simultaneously. Excel keeps track of the changes and provides appropriate prompts to handle conflicts.
Caution
Although the ability to share workbooks sounds great in theory, it can be confusing if more than a few users are sharing a single workbook. Also, be warned that this feature has been known to cause problems, and it’s certainly not 100 percent reliable. Therefore, use caution and make frequent backup copies of your workbooks.
You can share any Excel workbook with any number of users. Following are a few examples of workbooks that work well as shared workbooks:
Project tracking: You may have a workbook that contains status information for projects. If multiple people are involved in the project, they can make changes and updates to the parts that are relevant to them.
Customer lists: With a customer list, records are often added, deleted, and modified by multiple users.
Consolidations: You may create a budget workbook in which each department manager is responsible for his or her department’s budget. Usually, each department’s budget appears on a separate sheet, with one sheet serving as the consolidation sheet.
If you plan to designate a workbook as shared, be aware that Excel imposes quite a few restrictions on the workbook. For example, a shared workbook may not contain any tables.
In addition, you can’t perform any of the following actions while sharing the workbook (the relevant commands are grayed out in the Ribbon):
Delete worksheets or chart sheets.
Insert or delete a blocks of cells. However, you can insert or delete entire rows and columns.
Merge cells.
Define or apply conditional formats.
Change or delete array formulas.
Set up or change data-validation restrictions and messages.
Insert or change charts, pictures, drawings, objects, or hyperlinks.
Assign or modify a password to protect individual worksheets or the entire workbook.
Create or modify pivot tables, scenarios, outlines, or data tables.
Insert automatic subtotals.
Write, change, view, record, or assign macros. However, you can record a macro while a shared workbook is active as long as you store the macro in another unshared workbook (such as your Personal Macro Workbook).
To designate a workbook as a shared workbook, choose Review Changes 
Share Workbook. Excel displays the Share Workbook dialog box, shown in Figure 30.3. This dialog box has two tabs: Editing and Advanced. In the Editing tab, select the check box to allow changes by multiple users and then click OK. Excel then prompts you to save the workbook.
When you open a shared workbook, the workbook window’s title bar displays [Shared]. If you no longer want other users to be able to use the workbook, remove the check mark from the Editing tab of the Share Workbook dialog box and save the workbook.
Tip
Whenever you’re working with a shared workbook, you can find out whether any other users are working on the workbook. Choose Tools Share Workbook, and the Editing tab of the Share Workbook dialog box lists the names of the other users who have the file open, as well as the time that each user opened the workbook.
Excel enables you to set options for shared workbooks. Choose Tools Share Workbook and click the Advanced tab in the Share Workbook dialog box to access these options (see Figure 30.4).
Excel can keep track of the workbook’s changes—which is known as change history. When you designate a workbook as a shared workbook, Excel automatically turns on the Change History option, enabling you to view information about previous (and perhaps conflicting) changes to the workbook. You can turn off change history by selecting the option labeled Don’t Keep Change History. You can also specify the number of days for which Excel tracks change history.
While you’re working on a shared workbook, you can choose Office Save to update the workbook with your changes. The Update Changes settings determine what happens when you save a shared workbook:
When File Is Saved: You receive updates from other users when you save your copy of the shared workbook.
Automatically Every: Lets you specify a time period for receiving updates from other users of the workbook. You can also specify whether Excel should save your changes automatically, too, or just show you the changes made by other users.
As you may expect, multiple users working on the same file can result in some conflicts. For example, assume that you’re working on a shared customer information workbook, and another user also has the workbook open. If you and the other user both make a change to the same cell, a conflict occurs. You can specify the manner in which Excel resolves the conflicts by selecting one of two options in the Advanced tab of the Share Workbook dialog box:
Ask Me Which Changes Win: If you select this option, Excel displays a dialog box to let you determine how to settle the conflict.
The Changes Being Saved Win: If you select this option, the most recently saved version always takes precedence.
Caution
Notice that the second option, The Changes Being Saved Win, has slightly deceptive wording. Even if the other user saves his changes, any changes you make will automatically override his changes when you save the workbook. This option may result in a loss of data because you won’t have any warning that you’ve overwritten another user’s changes.
The final section of the Advanced tab of the Share Workbook dialog box enables you to specify settings that are specific to your view of the shared workbook. You can choose to use your own print settings and your own data-filtering settings. If you don’t place check marks in these check boxes, you can’t save your own print and filter settings.
Excel has a feature that enables you to track changes made to a workbook. You may want to use this feature if you send a workbook to someone for reviewing. When the file is returned, you can then see what changes were made and then accept or reject them accordingly.
To enable change tracking, choose Review Changes Track Changes Highlight Changes, which displays the Highlight Changes dialog box, shown in Figure 30.5. Then place a check mark in the Track Changes While Editing check box.
You can also specify the period to track (When), which users to track (Who), and specify a range of cells to track (Where). If you enable the Highlight Changes on Screen option, each changed cell displays a small triangle in its upper-left corner. And when a changed cell is selected, you see a cell comment that describes what change was made (see Figure 30.6).
After you select the option(s) that you want, click OK to close the Highlight Changes dialog box and enable tracking. To stop tracking changes, choose Review Changes Track Changes Highlight Changes again, and then remove the check mark in the Track Changes While Editing check box.
Caution
When tracking changes is enabled, the workbook always becomes a shared workbook—which severely limits the types of changes you can make. Shared workbooks are discussed earlier in this chapter (see “Sharing Workbooks”).
Following are some points to keep in mind when using the Track Changes feature:
Changes made to cell contents are tracked, but other changes (such as formatting changes) aren’t tracked.
The change history is kept only for a set interval. When you turn on Track Changes, the changes are kept for 30 days. You can increase or decrease the number of days of history to keep in the Highlight Changes dialog box (use the When setting).
If you would like to generate a list of the changes made, choose Review
Changes Track Changes Highlight Changes and then enable the List Changes On A New Sheet check box. Click OK, and Excel inserts a new worksheet named History. This sheet shows detailed information about each change made.Only one level of changes is maintained. Thus, if you change the value of a cell several times, only the most recent change is remembered.
To review the changes made while using the Track Changes features, choose Review Changes Track Changes Accept/Reject Changes. The Select Changes to Accept or Reject dialog box appears, enabling you to select the types of changes that you want to review. This dialog box is similar to the Highlight Changes dialog box. You can specify When, Who, and Where.
Click OK, and Excel displays each change in a new dialog box, as shown in Figure 30.7. Click Accept to accept the change or click Reject to reject the change. You can also click Accept All (to accept all changes) or Reject All (to reject all changes).
