with any migration of content from one system to another, the approach is usually to use ETL, Extract Transform and Load. Essentially you are extracting the content from the source system, then transforming this into a format that the target system understands and then you load it into AEM. This is a very basic overview, you can get more details in the links below. The extract/transform phase involves understanding the content in the source system and mapping the content/properties/metadata to the equivalent properties/values in AEM.
