Introduction to Merging

4

For explicit details on using Merging, together with an example, see Chapter 15, "Starting and Loading Merging."

Merging loads and displays two text files for side-by-side comparison, each in a read-only text pane. Merging marks lines that differ between the two files and displays a merged version in a third text pane. When automatically activated, the merged version contains two types of lines:

• Lines that are common to both input files (these lines always appear in the output file)

• Marked lines that are different in each file (these lines appear as the result of the default automerge process)

At the time you load the two files to be merged, you can also specify a third file, called the ancestor of the two files (which are called its descendants). When you have specified an ancestor file, Merging marks lines in the descendants that are different from the ancestor and produces a merged file based on all three files. To automatically merge (automerge) the two input files, you must specify an ancestor file.

Difference

Current, Next, and Previous Difference

Resolved and Remaining Difference

While focusing on a difference, you can accept a line from one of the original files, or you can edit the merged version by hand. When you indicate that you are satisfied with your changes (by clicking on a command button), the current difference is then resolved.

If the Auto Merge feature is on, Merging resolves differences automatically. For more information on how Merging resolves differences, see the discussion in "Merging Glyphs."

After a difference is resolved, Merging identifies it by changing its associated glyphs from solid to outline font. Merging then automatically advances to the next difference (if the Auto Advance property is on) or moves to the difference of your choice.

A remaining difference is one that has not yet been resolved.

Merging Window

Merging Glyphs

Two Input Files

• If two lines are identical, no glyph is displayed.

• If two lines are different, a vertical bar (|) is displayed next to the line in each input text pane, and the different characters are highlighted.

• If a line appears in one file but not in the other, a plus sign (+) is displayed next to the line in the file where it appears, and the different characters are highlighted.

• If a line is identical in all three files, no glyph is displayed.

• If a line is not in the ancestor but was added to one or both of the descendants, a plus sign (+) is displayed next to the line in the file where the line was added, and the different characters are highlighted.

• If a line is present in the ancestor but was removed from one or both of the descendants, a minus sign (-) is displayed next to the line in the file from which the line was removed, and the different characters are highlighted and in strikethrough.

• If a line is in the ancestor but has been changed in one or both of the descendants, a vertical bar (|) is displayed next to the line in the file where the line was changed, and the different characters are highlighted.

Table 4-1 summarizes the automerging algorithm. Ancestor is the version of a text line that is in the ancestor file; Change 1 is a change to that line in one of the descendants; Change 2 is another change, different from Change 1. Only when a line is changed differently in the left and right descendants does automerging fail.

Table  4-1 Automerging Rules Summary

Left Descendant	Right Descendant	Automerged Line
Ancestor	Ancestor	Ancestor
Change 1	Ancestor	Change 1
Ancestor	Change 2	Change 2
Change 1	Change 1	Change 1
Change 1	Change 2	No Automerge

When Merging automatically resolves a difference, it changes the glyphs to outline font. Merging lets you examine automatically resolved differences to be sure that it has made the correct choices.

You can disable automatic merging in the Properties window. When automatic merging is disabled, Merging constructs a merged file using only lines that are identical in all three files and relies on you to resolve the differences.

If you do not specify an ancestor file, Merging has no reference with which to compare a difference between the two input files. Consequently, Merging cannot determine which line in a difference is likely to represent the desired change. The result of an automerge with no ancestor is the same as disabling automatic merging: Merging constructs a merged file using only lines that are identical in both input files and relies on you to resolve differences.