XML Unordered Differencing and Merging

Comparing two or more files consists of identifying the parts that have been added, deleted, changed or moved. However, in many cases, movement is not such an important issue and does not necessarily lead to any fundamental differences. For example, moving a template in an XSLT file or a global complexType definition in an XML Schema does not alter the underlying meaning. As a result, normal (or Ordered) differencing can often report spurious changes and where many such moves have occurred in the input, the over-zealous reporting of such occurrences can render the differencing report useless. In light of this, the current release of Exchanger XML provides an Unordered differencing tool, specifically for those formats where document order is not an overriding concern when making comparisons. It goes without saying that this may not always be appropriate, particulary for textual data, and a future release will enhance the current offering with an Ordered Differencing mechanism as well. Note particularly that even when the two compared files are not identical, the Unordered Differencing tool may not always signal modifications.

Differencing

In the projects/XML Differencing project, open the files input/contacts.xsd and input/contacts2.xsd. Use the View->Split Vertically function to visually compare the two files side-by-side. Notice how some elements/attribues have been added, deleted, changed and moved. Now open the differencing window by selecting Tools->XML Diff and Merge.... In the dialog, choose contacts.xsd as the Base URL and contacts2.xsd as the Modified URL.

Figure 1. XML Diff

A tree view will be displayed to show additions (in Green), deletions (in Red) and changes (with the new version in Blue and a line through the original). An asterisk is displayed on any element that contains a difference (either directly or in a descendant node). Use the normal "+" and "-" buttons to expand and collapse the tree nodes and use the Show First Difference button , Show Next Difference , Show Previous Difference and Show Last Difference buttons to easily navigate between the reported changes. Notice how the XPath for the location of each diffference is shown in the status bar at the bottom of the window - this is useful if you want to navigate to the difference outside of the Diff window. Notice also that although the relative positions of the Contacts and Address element definitions have changed between the 2 files, no difference is reported for this as it is not significant.

Merging

Changes in the Modified document can be selectively merged on top of the Base document using the Merge Tree. Click the Show Merge Tree button on the XML Diff and Merge toolbar and a second tree view will appear to the right of the original view.

Figure 2. XML Merge

Navigate to the first difference (the Firstname element definition) and right-click with the mouse placed on the highlighted difference in the Diff view. A pop-up will appear asking if you would like to use the Modified version or just retain the Base version. Choose to use the Modified version and it will appear in the Merge Tree on the right-hand side, highlighted in pink.

Figure 3. XML Merge Using Modified Version

To undo the merge and revert to original version, simply click right-click again on the difference in the Diff Tree and this time choose to use the Base version. The modified (pink) element definition will disappear and revert to its original form.

Now, in the Diff Tree, navigate to the fourth change, the "deleted" node that was an element reference for Address. Right-click with the mouse on the highlighted difference and you will be prompted to choose whether or not to delete the node in the merged version. Choose Delete and the node will be removed in the Merge Tree. Navigate to the last change in the Diff Tree where an attribute definition has been inserted in the Modified version, and a right-click will prompt whether or not to insert the new node in the merged version. Choose to Insert and the node will be added to the Merge Tree, again highlighted in pink. Note that when the Merge Tree view has focus, the navigation buttons apply to it and move the cursor to the first, next, previous and last changes that have been merged.

When you have completed the merging process, press the Edit on the top right of the Merge Tree to create a new document that can be further edited or saved to disk and then close the Diff/Merge window.