Canto: a Hypertext Data Model

The Canto hypertext data model is characterized by a hierarchical schema mechanism that allows a predetermined, open-ended schema to be embedded in the hyperdocument. Canto uses two types of nodes: concept nodes, which provide organizational structure, and information nodes, which contain text and other data. The operations provided by the Canto Data Model are defined formally using the Z specification language. The Canto Schema Language gives the hypertext designer access to these operations. We show that the operations defined in Canto preserve properties of accessibility and data integrity. We evaluated Canto with a controlled experiment involving human users. These tests showed that a hypertext system developed with Canto was easier to use than an otherwise similar system that did not employ a schema mechanism.Severalapplications have been developedusing Canto. One such application, which we describe in some detail, involves the use of Canto to teach students the skill of program reading.