15. A distributed parallel processing system according to claim 11 , wherein: said data store includes said data structure created by said manager based on said description; said data structure represents said graph; said one or more identifications of vertices include one or more unique identifications and information about software for one or more vertices; said one or more identifications of edges include one or more unique identifications and indications of two or more vertices; said one or more identifications of inputs identifies at least one vertex; and said one or more identifications of outputs identifies at least one vertex.
11. A distributed parallel processing system, comprising: at least one or more processors; a network; a plurality of computing machines connected to said network, where the computing machines comprises the at least one or more processors; a data store that stores a description of a user customizable graph, said user customizable graph includes a set of vertices corresponding to a set of program units to be executed and edges corresponding to data channels, said description of said graph includes syntax for replicating, connecting and merging sub-graphs, said connecting includes connecting a first output of a first sub-graph only to a first input of a second sub-graph, and connecting a second output of said first sub-graph only to a second input of said second sub-graph; and a manager connected to said network and in communication with said computing machines and said data store, said manager manages execution of a job defined by said graph, said manager reads said description and builds said graph based on said description, said manager assigns said program units for execution on said computing machines based on said graph, said manager creates a data structure that includes one or more identifications of the set of vertices corresponding to the set of program units to be executed, one or more identifications of said edges, one or more identifications of inputs and one or more identifications of outputs, said manager identifies at least one vertex ready for execution according to inputs associated with the vertex and creates an execution record including a ready state associated with the at least one vertex identified.