To compare two Salesforce data models, follow these steps:
1. On the main menu, navigate to “Tools | Compare”.

2. In the “Compare” window, you must now select the target
data model. Click the Browse button
and
load the data model file you want to compare with (The file extension should
be “.ABLX” or “.ERB” for the older projects).
Note: The source model is the opened project.

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Available in: Standard, Professional and Enterprise Editions |