Major Relationships are expressed in CSDL as binary associations with association sets; navigation properties reference these associations and describe target and source "ends" of these associations.
The requirement of defining binary associations for each relationship makes the CSDL more verbose, harder to read, and moves the information that is interesting about the navigation property out of line.
A simpler way to express navigation properties is summarized in the following presentation, presented at the first OData TC Meeting in July:
https://www.oasis-open.org/apps/org/workgroup/odata/download.php/46576/Association%20Simplification.pptx.
A complete proposal would be the application of these concepts to [OData-CSDL].