A highly customizable, portable, and fast control can deal with huge data sets and be tuned for use in many applications, avoiding such common problems as bad performance and usability issues such as the inability to present big data sets in clear way.

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By Egor Kazachkov, software engineer, Data Visualization Controls team, Intel Corp.

This paper is intended for GUI developers who want to write portable, reusable, and fast controls for visualizing big and complex data. There are some common problems such as bad performance and usability issues such as the inability to present big data sets in clear way, so the user can easily navigate and analyze it. Also, program data structures and visual data representation often becomes very dependent. Thus control becomes very specialized and cannot be used in other applications without making significant changes. This paper presents an approach to design complex controls that allow solving the problems discussed above. In this paper, examples of the graph viewer control are used to illustrate the basic ideas. These ideas can also be applied to a variety of other controls.

Definitions
A Graph is a set of objects and relations between them. Objects are called nodes. The relation between the nodes is called edges. So, a visible graph is a set of nodes (squares, rectangles, circles with or without labels, and so on), and edges (lines or curves) connecting the nodes. The algorithm that defines the position of the nodes and edges is called a layout.

Note that the nodes can contain other nodes and edges (subgraphs). All nodes that have edges going from them to any given node are called parents of this node. All nodes that have edges going to them from any given node are called children of this node.

Common problems in graph control
There are many applications where graph control can be used for visualizing data. If you want to use the same graph control for different applications you must provide a way to customize it. Any such customization must not affect the performance of the application. Following is a list of possible problems that you may encounter when you apply control to different applications:

• Appearance of nodes and edges. Graph elements may either have a different color and shape, or may or may not have a text label, and so on. It is impossible to predict the appearance of the graph elements and implement them in advance. Also, there are a lot of possible graph layouts used in different cases. You may need a way to change this according to the application.