Get the Fields Available for Retrieval
By getting the fields available for retrieval, you can identify what kind of information is returned on a Retrieve call.
The Retrievemethod takes a list of properties to retrieve on a given object. To build a dynamic list of retrievable properties, use the Describe call and filter out the retrievable fields using the IsRetrievable property.
You can use the Describe method to build your integration. However, do not use this call before every Retrieve call. These fairly static nature of these values make frequent retrieval impractical and unnecessary.