A hypertext system may allow different types of links. The link type can reflect the type of information it is pointing to, making it possible for the user to only view links of a certain type. Different types of links in a document could be references to related articles or reviewers' annotations. To represent this variety of link types, links can have attributes just like nodes.
An important point in hypertext is the support for collaborative work. If several people are reviewing and annotating the same hypertext, they all use the common network made by the author of the document. To this common network each individual can add a personal subnetwork reflecting their own need for referencing across the common network and including references for their annotations. (This is exactly how annotations work in the WWW-browser Mosaic for X.)
A handle is a part of the text inside the slot to which a link can be attached. Handles make it possible to establish connections between the contents of one node and another node. A handle is defined as a consecutive sequence of characters in the textual contents of the slot. It is identified by (the node id and by) its character position in the text and the span in numbers of characters.
When a link is anchored to a handle, that is, there is an outgoing link from a handle, the text span specified by the handle is called a button. When the end-point of a link is a handle it is called a field. The difference between buttons and fields is purely a conceptual one.
Nodes, slots and fields have been discussed as destination points for links. Links pointing at links, called second order links, can be used to point at a collection of connections. It might reflect that a link itself is of special interest, and that the reader, after being guided to the link, can chose to study the anchor or destination of the link. Links are identified as connection points by name of the network in which they are embedded, together with their own name.
Active links are links that have anchors or destinations that are function denotations. That is, instead of having links pointing at fragments of text they contain a function. This function is to be interpreted when you follow the link. This kind of link can be used to generate a view of the data it is anchored to. That could be the generation of a graphical representation of the data each time one is following the link. A function signature is added to the domain of anchors and destinations. The domains of the arguments and the results of the function are not specified in any further detail within the reference model.
The use of the set-structure fits well into card-like hypertexts. The map-structure can extend this unordered collection of cards with a facility of direct access by user-defined names. Sequences can be used to express interrelationships between nodes as the sequence in which they should be visited, e.g. chapters in a book. Defining these structures recursively makes it possible to make tree structures of nodes.
It should be emphasized that it is not the nodes and networks themselves that are organized in these structures. The structures contain only the names of the nodes and networks. Hence it is possible to reuse nodes and networks in several structures. E.g., one can think of a section or figure appearing in more than one book, and thus in several structures.
Structures can be interpreted by filters, to make linear representations of the hyperdocument, e.g. on paper. A tree structure of a book should intuitively be interpreted by a filter in a top-down, left-to-right manner, so that chapter one and the subsections of this chapter are written out before chapter two and so on.
Structures are uniquely identified by their name. Each structure is characterized by having a collection of substructures, each organizing destinations into sets, sequences or maps. The substructures themselves have unique identities and can be destinations, thus making it possible to build more complicated structures. A structure has a root that can identify one of the substructures as being the root of the structure.