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Design Principles and Goals

The graphics design is driven by two observations, neither of which is controversial nor especially insightful, but which do have a far-reaching and clarifying effect:

1.

There are a small number of graphical tasks which come up again and again in the analysis and exploration of radio astronomy data.

2.

These tasks will appear in many different contexts and combinations, some of which we cannot anticipate.

These observations lead quite directly to the following principle of design: AIPS++ must provide a set of GUI components, which are easy to combine and configure, and which may be extended in the future by subclassing. Each GUI component shall be designed so that it can

• be called from an otherwise non-graphical program, thus freeing the casual programmer from learning the intricacies of computer graphics

• assembled, along with other components, into a fancy, integrated application, with many controls and options

• appear as part of a stand-alone application of narrow focus, for example: the AIPS++ TableEditor allows many tables to be viewed simultaneoulsy, with a small control panel providing centralized control (for iconifying and deiconifying windows, raising windows to the top, and opening new windows)

• called and manipulated from the glish command line, or from any process connected to the glish ``software bus''.

• has (as much as possible) an abstract public interface, which describes what the component does: most window-system-specific details should be hidden from view.

Some further principles of design:

3.

Many of the graphical tasks we want to perform are neither unique to our project nor cheap and easy to build, so we should adopt and adapt existing software into our own system whenever possible.

4.

From the start, we should anticipate the problems that will be posed by ``creeping featurism'' as the years go by, and as our components are put to highly specialized and presently unforseen use.² The best way to prepare for these future uses is by the careful use of inheritance: the latest special purpose plotter component, for example, should be just a subclass of a plotter we've already written.