WHAT IS DIFFERNCE BETWEEN DEF FORMAT AND GDS II FORMAT?

WHAT IS THE DIFFERNCE B/W DEF FORMAT AND GDS II FORMAT?
WHAT ARE THE INFORMATION WILL BE AVAILABLE IN BOTH? WHEN THEY WILL BE PREFERED OVER ANOTHER?

THANKS IN ADVANCE

DEF => Design Exchange Format,

Design Exchange Format (DEF) is an open specification for representing physical layout of an integrated circuit in an ASCII format. It represents the netlist and circuit layout. DEF is used in conjunction with LEF to represent complete physical layout of an integrated circuit while it is being designed.

GDS II stream format, commonly known as GDSII is a database format, which in the integrated circuit industry has been the de facto standard for IC layout data exchange for more than two decades
Originally it was designed as a format of data files used to control integrated circuit photomask plotting. Despite its limited set of features and low data density, it was ubiquitously used for transfer IC layout data between design tools from different vendors which operated with proprietary data formats.

GDSII files are considered to be the final output of the IC design cycle and are passed to IC foundries for IC fabrication. These GDSII files were originally produced on magnetic tapes, hence the final moment of the IC design process became known as tapeout

LEF (and DEF) format contains information only about metal layers. Information about layers like poly, n-well etc are not represented. The reason is that you only need metal layer layout knowledge to perform place and route.

GDSII format is a complete layout description that contains all layers and is the file that is sent to foundry. Hope this helps