a special set of nodes usually called u2018 leaf u2019 nodes for the dsu tree u2018 leaf u2019 nodes signify that no further distinction between related elements is required a node with a u2018 parent u2019 and u2018 children u2019 is called a u2018 branch u2019 the u2018 lineage u2019 or u2018 ancestry u2019 of a node refers to its u2018 parent u2019 its parent 39 s u2018 parent u2019 and on and on up to and including the u2018 root u2019 the set of nodes with the same u2018 parent u2019 are called u2018 siblings u2019 the dsu tree structure of the invention supports two important concepts inheritance and membership a u2018 child u2019 node inherits information from its u2018 parent u2019 for example suppose that a dsu for a history test is called u2018 history u2019 and it has two u2018 children u2019 nodes one called u2018 wwi u2019 and one called u2018 wwii u2019 this indicates that this history test is made up of a set of questions on world war i and another set of questions on world war ii further suppose that the test is essay based such that each section has several prompts to which the test takers must respond this test has a special scoring model requirement that every essay must be assessed twice within the data model this information need only be configured for the u2018 history u2019 dsu node because the fact that u2018 history u2019 is double scored implies that u2018 wwi u2019 question and u2018 wwii u2019 questions are also.