The DZR and DZS extensions are used to identify the format in which The Wind Waker stores the data for a stage's object layout. DZR is used for rooms, and the layouts defined within it are local to that room, while DZS is used for stages themselves, which means that their layouts are always active, independent of what room is currently loaded.
The format made a return in Twilight Princess, albeit with several new chunk types. It was later changed completely in Skyward Sword, though .dzr and .dzs still remain the extensions used for the game's object layout files.
The file header is simply an integer indicating the number of chunks the file contains.
//4 bytes long /*0x00*/ int NumChunks;
A chunk header is made up of a MAGIC denoting the chunk type, the number of entries within the chunk, and the offset of the chunk's first entry. The format of the entry depends on the chunk type.
//0xC/12dec bytes long /*0x00*/ string ChunkMagic; /*0x04*/ int NumEntries; /*0x08*/ int FirstEntryOffset;