simple representation of a 3D object. e.g. protein. Most data in pdb file is either a feature or a mapped alignment, no need to provide it here. Structure service is really for serving 3D coordinates, not annotations description of object. id e.g. 1tim.A,8tim.B, P001228, ...; type: type of object e.g.: protein, dna. version: last time this object has been changed (sometimes not so easy to know ...) contains multiple groups. A structure can consist of several chains. a group of atoms representing e.g. a single amino acid or a hetero atom. Most of the time will occur within a chain. But there are groups that can occur without clear association to a chain.e.g. H2O. type: amino,nucleotide, hetatom; groupID: PDB code of aminoacid e.g. 25,26,27A. name: name of amino acid. single letter code tony! a single atom. x,y,z: coordinates. atomName e.g. N,CA,C,O,CB,... atomID: e.g. 148,149,150A,151B a group of atoms representing e.g. a single amino acid or a hetero atom. Most of the time will occur within a chain. But there are groups that can occur without clear association to a chain.e.g. H2O. type: amino,nucleotide, hetatom; groupID: PDB code of aminoacid e.g. 25,26,27A. name: name of amino acid. single letter code tony! a single atom. x,y,z: coordinates. atomName e.g. N,CA,C,O,CB,... atomID: e.g. 148,149,150A,151B connectivity between atoms. not mandatory for amino acids but mandatory for HET! atoms that are connected