The purpose of the system to capture not only the content of a document but also its structure. The point of capturing the structure is that it contains information too, and when one have multiple documents in the system based on structure information possible to make connections between content and structure.
In order to be able to store content in useful fashion we need to know the structure of the document we want to work with. When capturing the structure we use multiple and nested objects.
A Source describes from we get or request information. It can be and url or organization name, like Gutenberg.org or any unique identifier.
SourceFormat object describes the document format belongs to a source. A Source can be an url, for example a blog from where we query RSS feed, or content in defined format, for example text files from Gutenber.
Understanding what is DimensionStructure one need to be aware of that in this system a document is considered as tree structure. In this tree the nodes may or may not contain information. These nodes are the DimensionStructure objects. However, in the implementation the tree is built by DimensionStructureNode objects. The reason is that we need to separate the information and functionality of a node. Information is the DimensionStructure, while tree functionality is captured in DimensionStructureNode objects.
In case of text a DimensionStructure can be a paragraph, a sentence or a word. In case of HTML document a DimensionStructure can be text wrapped in a HTML tag.
DimensionStructureNode describes the tree structure of DimensionStructures. They provide a wireframe of the document and that objects, like DimensionStructure, can be added to nodes.