Unknown Node Types

It may often happen that you read in a file of FARFALLA trees containing nodes that you do not manipulate in your program. The file may be part of a generic DST and someone else at your site has required the creation of some nodes containing information you do not care about. Or the file may have been produced by someone else at another institution using nodes that were custom-developed there, and they give you a copy of the file and ask you to use your software to do some reconstructions, add some nodes to the trees, and give it back to them.

Because FARFALLA's input strategy is to create objects that read themselves off disk, it cannot create nodes of a type that has not been declared to FARFALLA. (Remember that if any routine in your executable #includes the .h file for a FARFALLA node class, that node type is automatically declared to FARFALLA at execution time.) When the FARFALLA input routine encounters a node type that has not been declared, FARFALLA creates an unknownNode. The node will be linked onto the tree as a node of type unknownType. However, in its data area it will contain an indication of what the original node type on disk was. Usually your software will completeley ignore any unknown nodes on the tree.

If you later output the tree to disk, the data from the unknown node will be written to disk in its original form, not as an unknownNode. The following sequence of events illustrates the operation of unknownNodes:

• User A at Boston creates a node type containing QTP information.

• User A creates a DST including erpNodes, wireTrackNodes and qtpNodes.

• User A sends a copy of the DST to User B at Caltech.

• User B runs software that knows nothing about qtpNodes. When B's software inputs a tree from disk, all the data from a qtpNode is read into memory as an unknownNode.

• User B's software matches erp hits to tracks and creates a matchNode which is added to the tree.

• User B's software writes the trees back to disk to a new DST.

• User B sends a copy of the expanded DST to User A.

• When User A's software inputs the expanded tree from disk, the QTP information is in a legitimate qtpNode.