Generally, while VRTs are statically defined, VRs are dynamically generated at runtime to be displayed. A visual file is a set of VRs of the same type. VRs belong to formats or to visual access structures. It is often appropriate that more than one format be defined for the same entity, to fulfill the requirements of different interaction contexts. VASs are generally instantiated runtime, to be linked to actual VRs.
Indexes are typical VASs.
The visual design must satisfy operational constraints such as screen limitations and response-time requirements. The first subtask requires to define schemata and layout of VRTs, and connections among VRTs. Definition of visual record schemata Given an interaction task, usage parameters must serve as primary guidelines for the partition of the entity, which defines the allocation of individual data items to separate VRTs. Definition of inter-record connections Logically, data items related to a single entity are still considered to be connected, and links among entity segments must guarantee such connectivity. In this step, given a VRT schema, the data item presenters and the spatial relationships among them are defined.