Holon implements a structure of modules, sections and units. The units contain the actual source; the sections and modules (or chapters) serve as headers and provide space for additional comments.
Each item (unit, section, module) has its own record in the linear database. The order of the database items is independent of the browser structure, it is simply the order of creation of the items.
The structure is implemented with three fields in the database records:
next -- points to the next item on the same level (next chapter, next section, next unit)
list -- points to the first item on the lower level (from a chapter to the list of its sections, from a section to the list of its units, the list field in a unit is empty).
active -- points to the currently active item in the list.
The pointer to the first chapter is kept in the system base. The system base is a separate list in the database that contains the system parameters.