Contains model declarations and usages.
Revert "Contains model declarations and usages."

This reverts commit 116ad31b9fed54d7ab2d8e71d2bce44fc75862d9.
Revert "Revert "Contains model declarations and usages.""

This reverts commit 5da23f66e2acf780a27139edf33afa067d5579d5.