1. A computer-implemented method for concern-based processing of a directed acyclic graph (DAG) among one or more DAGs using aspect-oriented programming comprising: instantiating a plurality of aspects for processing a DAG, each aspect of the plurality of aspects associated with one concern for processing the DAG, the DAG comprising a plurality of nodes, whereby the plurality of aspects have been separately coded in response to previously identified and subsequently removed concerns for processing the DAG, the plurality of aspects comprising: a first aspect for determining the structure of the DAG, a second aspect operable to compare each node in a subset of the plurality of nodes to a condition and to remove the compared each node from the subset of the plurality of nodes that satisfies the condition, and a third aspect for processing the subset of the plurality of nodes based on the determined structure of the DAG and a type of each node of the subset of the plurality of nodes, the third aspect comprising an extension of the first aspect; selecting the DAG from among the one or more DAGs; and processing the DAG based on at least the first and third aspects.