5. A computer readable storage media embodying computer readable program code for execution by a processing device, the computer readable program code adapting the processing device for capturing expert knowledge and data, the computer readable program code comprising: receiving expert knowledge and data entered via an editing device; storing the received expert knowledge and data into one or more tables of a database system, a first subset of the data being represented in the one or more tables as conclusion data, a second subset of the data being represented as observation data, and a third subset of the data being represented as relationship data; and generating based on the one or more tables a probabilistic model that captures entered expert knowledge and data, the probabilistic model including a structure of layers of nodes with at least one grouping layer disposed in-between a conclusion layer having a plurality of conclusion nodes designated as parent nodes and formed based on the stored conclusion data, and an evidence layer having a plurality of observation nodes designated as children nodes and formed based on the stored observation data, wherein a group node in the at least one grouping layer represents an aggregation of conclusions in two or more of the conclusion nodes in the conclusion layer, wherein the structure of layers of nodes includes directed arcs between the nodes based on the stored relationship data, with none of the directed arcs connecting two nodes in a same layer, and wherein at least one of the arcs is between the group node and at least one of the plurality of observation nodes, wherein, the generated probabilistic model is configured to be invoked by a reasoning engine for outputting probabilities of one or more conclusions or aggregation of the conclusions, in response to input observations, during a decision making process.
8. The computer readable storage media of claim 5 , wherein the structure of layers of nodes further includes a plurality of grouping layers of increasing levels, and the structure of layers of nodes further comprises: a first set of one or more directed arcs, each directed arc of the first set originating at a node of the conclusion layer and ending at a node of a grouping layer of a first level; if there is more than one grouping layer, a second set of one or more directed arcs, each directed arc of the second set originating at a node of a first grouping layer of any level and ending at a node of a second grouping layer of any level, the level of the first grouping layer being one less than the level of the second grouping layer; and a third set of one or more directed arcs, each directed arc of the third set originating at a node of the conclusion layer or at a node of any of the grouping layers, and ending at a node of the evidence layer.