The graphical XP environment is, in essence, a shell that acts as an interpreter between the user and a model. The XP graphical interface provides the user with a very high-level interface to various numerical simulation programs oriented towards solving problems that may be represented as some form of link-node structure.
The main theme of this interface is Decision Support Graphics. At the front end of the interface the process of creating data for the model is made as visual as possible, with the aim of emulating real world problems as closely as possible. For example, most dialogs contain graphics that visually link the data being entered to the physical system being modelled.
The user is given continual guidance and assistance during data entry. For parameters that are difficult to estimate, the user may be advised of literature to aid in selecting a value, or an explanation of a parameter and some proposed values may be shown on the screen. If there are other ways to pick the value, typically, if the parameter is a function of other variables, the equation is shown to the user.
The user interface is intelligent and offers expert system capabilities based on the knowledge of the software developers and experienced users. For example, as various graphical elements are connected to form a network, XP filters the user's actions so that a network that is beyond the scope of the model is not created. The general philosophy is to trap any data problems at the highest possible level - at the point the users create the data.
At the back end of the user interface the results of model analysis and design are presented graphically to maximize comprehension, assist in the interpretation of results and support decision-making.