Recently I am working with Windows Installer and think ProductCode, UpgradeCode and PackageCode are very basic but very important concepts, so I make a conclusion here for references. Both ProductCode and UpgradeCode can be viewed from Property table in MSI package, and PackageCode can be reviewed from View->Summary information if you view MSI through Orca (which is shipped with Windows SDK.)
What is UpgradeCode in the MSI package?
The upgrade code is the unique GUID of identifying a family of a product. That is, the same products with different versions have probably been shipped for a few releases. These products have different ProductCodes, but they are linked together by using SAME UpgradeCode. For example, assuming that we wrote a product called "Happy MSI" and this product only has one MSI package for deployment on client system. The first release of this product is actually the MSI package with name "version_1.msi", and the second release is "version_2.msi". Then, these two MSI must have same UpgradeCode. When users run "version_2.msi" on their system, the windows installer will use the UpgradeCode to decide if previous versions of this product are already present on the system. Installer API "MsiEnumRelatedProducts()" uses the UpgradeCode to query all the family products.
What is ProductCode in MSI Package?
The product code is the unique GUID of identifying an application or product release; In other words, different versions and languages of Product must have different product codes. http://msdn.microsoft.com/en-us/library/aa370854(VS.85).aspx. Also, ProductCode can be used to query feature state, and product state. For example, installer API "MsiQueryFeatureStateEx()" and "MsiQueryProductState()", etc.
What is PackageCode in MSI Package?
Similar, the package code is the unique GUID identifying a particular Windows Installer package. Here, package mapps to a physical file with extension name ".MSI". Remember, a product consists of one or multiple (MSI) packages, and one package also can be shared among different products. The combination of ProductCode and PackageCode is used to determine if the users want to reinstall the product or not. I found the book "The Definitive Guide to Windows Installer" has the best explaination on this. There are four scenarios: