Common User Access

Common User Access (CUA) is a set of guidelines for the user interface to personal computer operating systems and computer programs, developed by IBM in 1987 as part of their Systems Application Architecture. Used originally in the OS/2 and Microsoft Windows operating systems, parts of the CUA standard are now implemented in programs for other operating systems, including Mac OS X and Unix.

The CUA contains standards for the operation of dialog boxes, menus and keyboard shortcuts that have become so influential that they are implemented today by many programmers who have never read the CUA.

Some of these standards can be seen in the operation of Windows itself and DOS-based applications like the MS-DOS 5 full-screen text editor EDIT. CUA hallmarks include:

• A menu bar across the top of the screen;
• Menus opened by pressing Alt plus the underlined letter of the menu name; alt on its own activated the menu bar;
• Menu commands which require further information are indicated by a suffixed ellipsis ("...");
• Options are requested using dialog boxes;
• Navigation within fields in dialog boxes is by cursor key; navigation between fields is by pressing [Tab] or [Shift]+[Tab] to go backwards;
• Dialog boxes should have a "Cancel" button, activated by pressing the [Esc] key, which discards changes, and an "OK" button, activated by pressing [Return];
• The program should have online help, with a Help menu as the last option on the menu bar; context-sensitive help should be summoned by pressing [F1];
• The first menu should be called "File" and contain operations for handling files, quitting the program and so on; the next is called "Edit" and contains cut, copy, paste commands; the next is "View";
• The Cut command was [Shift]+[Del]; Copy was [Ctrl]+[Shift]+[Del]; Paste was [Shift]+[Ins]
• And so on.

CUA was a detailed specification and set strict rules about how applications should look and function. Its aim was in part to bring about harmony between MS-DOS applications, which until then has existed in a hell of totally different user interfaces.

Examples:

• In WordPerfect, the command to open a file was [F7], [3].
• In Lotus 1-2-3, a file was opened with [/] (to open the menus), [W] (for Workspace), [R] (for Retrieve).
• In Microsoft Word, a file was opened with [Esc] (to open the menus), [T] (for Transfer), [L] (for Load).
• In WordStar, it was [Ctrl]+[K]+[O].

Some programs used [Esc] to cancel an action, some used it to complete one; WordPerfect used it to repeat a character. Some programs used [End] to go to the end of a line, some used it to complete filling in a form. [F1] was often help but in WordPerfect that was [F3]. [Ins] sometimes toggled between overtype and inserting characters, but some programs used it for "paste".

Thus, every program had to be learned individually and its complete user interface memorized. It was a sign of expertise to have learned the UIs of dozens of applications, since a novice user facing a new program would find their existing knowledge of a similar application absolutely no use whatsoever.

This detailed specification drew some of its inspiration from Apple Computer's lavishly detailed Human Interface Guidelines. The Apple HIG is a detailed book specifying exactly how software for the Apple Macintosh computer should look and function. When it was first written, the Mac was new and GUI software was a novelty, so Apple took great pains to ensure that programs would conform to a single shared look and feel. CUA had a similar aim, but faced the more difficult task of trying to impose this retroactively on an existing, thriving but chaotic industry.

However, CUA did not only cover DOS applications; it was also the standard to which the user interface of Windows was designed, as well as that for OS/2 applications - both text-mode and the Presentation Manager GUI - and IBM mainframes which conformed to the Systems Application Architecture. Thus CUA was more than just an attempt to rationalise DOS applications - it was part of a larger scheme to bring together, rationalise and harmonize the overall functions of software across IBM's entire computing range, from microcomputers to mainframes, their UIs, functioning, communications and storage protocols. As this encompassed PCs and compatibles, it extended to the entire PC industry - which is perhaps part of the reason it was not completely successful.

References

• IBM, Systems Application Architecture: Common User Access: Panel Design and User Interaction, Document SC26-4351-0, 1987.
• IBM, Systems Application Architecture: Common User Access: Advanced Interface Design Guide, Document SC26-4582-0, 1990.
• IBM, Systems Application Architecture: Common User Access: Basic Interface Design Guide, Document SC26-4583-0, 1990.