1. A computerized method for processing a graph containing a set of nodes, said method comprising: providing a forest of trees comprising two or more trees, the forest of trees corresponding to a directed acyclic graph containing a set of nodes, each of said nodes having a type chosen from a set of types comprising at least an observation node type which implements receivers of one or more events, an invocation node type which implements calls to start one or more other activities, and a control node type which implements one or more control structures; determining a depth for each node in said forest of trees; in a breadth-first traversal manner, checking compliance of each node in said forest of trees with a model by comparing the node depth and node type of each node in said forest of trees to a predefined matrix providing at least four columns with each column representing a semantic level of node depth and each successive one of the columns being hierarchical dependent on a preceding one of the columns, said matrix defining following actions to be carried out: no action, creating a new sub-tree, triggering exception handling based on each node depth and node type combination; wherein no action is carried out upon determining that the node type is allowed in an actual matrix-column, a new sub-tree is created upon determining that the node type is not allowed in an actual matrix column and the not allowed node type is shifted to a next following column and exception handling is triggered upon determining that the node type cannot be shifted to the next following column; in response to the comparing, non-compliant nodes are normalized by performing action defined in said matrix.