Rafael:
We integrated to Navision several years ago, and it was not especially difficult. Like any integration, the biggest effort is getting the file contents and layouts agreed on. Unless the Navision API has vastly improved, the process will likely be via flat file exchange - XML format. If your Clarity instance is On Demand, files from Navision, probably Resource data, possibly Non-labor costed items, will be FTP'd to the Clarity SFTP site, and then a process run to XOG them in. And, most likely you will need to FTP files like time and/or costed time from the Clarity SFTP site to a location inside Navision environment and then import them from there. If you have the ability to set up a direct Web file exchange with Navision, the process can be a little simpler, but many organization's security teams do not allow that. Also, if your Navision instance supports REST, that might be used for Resource data (depending on being v14.3 or above), but it will be a while before there will be much in the way of other useful data exchanges with REST.
John