The Storage Layer

The storage layer describes the structure of a hypertext as a finite set of components together with two functions: a resolver function and an accessor function. These functions are responsible for retrieving components, such as mapping specifications of components into the components themselves.

In the storage layer, the basic unit and fundamental addressability is the component, it can be an atom, a link or a composite made up from other components.

Atom component

Typically thought of as nodes in a hypertext system (e.g. cards in NoteCards, frames in KMS, documents in Intermedia, statements in Augment).

Link component

Link is an entity to represent relationship between components. A link specifier consists of a component specification, an anchor id, a direction and presentation specification. Link component is basically a sequence of two or more "endpoint specifications" each of which refers to (a part of) a component in the hypertext. Links also have directions. The direction indicates whether the end point is to be considered as a source (FROM), a destination (TO), both a source and destination (BIDIRECT) or neither a source nor destination(NONE).

Composite component

Just a component which is composed of other hypertext components. For example, the content of a composite component may be composed of two atomic components, one composite component and two link components.

Each component is globally unique identify by its unique identifier (UID). The accessor function of the hypertext is responsible for "accessing" a component given its UID, i.e., for mapping a UID into the component "assigned" that UID. UIDs provide a guaranteed mechanism for addressing any component in a hypertext document. Another function is the resolver function, it task is to help component specification resolve to a UID, which then can be used to access the correct components.