CHCS and DHCP FileMan both offer developers the ability to build "CHUI" (Character-oriented User Interface) screens which will handle input to FileMan databases. In both systems, the name "ScreenMan" has been used to designate the subset of FileMan utilities that handle the building and running of these screen-oriented input sessions. In DHCP, the sequence of screens used in one such session is called a "Form".

The two "ScreenMen", developed quite independently, have some basic characteristics in common. For example, both use a transaction-oriented mode of processing: the user enters data (usually for a single Entry in a File, although both systems allow "Relational Jumps") into the windows on one or more screens, and only when he has completed this sequence of input is the data filed, en masse, into the FileMan database. The user can always abort the data-entry process at any point up until the final filing, in which case no change to the FileMan database takes place at all. (In both systems, the exception to this rule is that a deleted Entry or Multiple Field remains deleted even if the data-entry session is subsequently aborted.) Furthermore, in both systems the developer can write MUMPS code that controls "branching logic" from one window to the next, or that intervenes between the user's input and the filing, to evaluate and/or validate the data entered before it is written into the 'real' FileMan globals. Both systems allow "display-only" literals or Computed Expressions to be put anywhere on the screen.

Unfortunately from the standpoint of portability, the differences between the two systems are more striking than the similarities. The discussion below will make two basic points:

  1. From the end-user's standpoint, the data-display and data-entry conventions of the two systems are different enough that 'cross-training' between the systems would certainly cause some annoyance and confusion for most users.
  2. From the developer's standpoint, and from the standpoint of internal Global structure, the way in which screens are designed, created and organized is completely different in the two systems. This, disappointingly, means that a screen developed in one of the systems is unlikely to be automatically portable to the other system.

A. Incompatibilities in Screen Layout

Any porting of CHCS screens to DHCP would be particularly problematic because of the fact that CHCS ScreenMan allows data entry to take place on lines 2 through 23 of the 24-line screen, whereas DHCP ScreenMan allows data entry only on lines 1 through 17. Thus, in general, it would be impossible simply to map the graph-paper design of a screen in CHCS into a layout acceptible to DHCP. Given the way existing CHCS application screens have been designed, taking full advantage of 22 editing lines, it would be typical that one CHCS screen would have to be 'mapped' to two DHCP screens.

Porting to CHCS would seem to be more straightforward; seventeen lines, one supposes, can always fit in a 22-line space. Even here there are caveats, however.

First of all, DHCP ScreenMan allows a data window, as it appears on screen, to be shorter than the allowed length of the corresponding data being edited. In fact, when the DHCP user is editing a very long free-text field (say, 200 characters long), the screen necessarily shows (perhaps misleadingly?) only a trucated version of the data (no more than 80 characters, depending on the screen designer's specification). In this case, the user accomplishes the entry of the "overflow" characters either by continuing to type, and watching his input "wrap around" out of view, or else (in Version 21) he hits a special keystroke sequence to invoke multi-line "Zoom editing" in the "Command Area" at the bottom of the screen. CHCS ScreenMan, on the other hand, allows one to edit only what one can see; free-text data longer than 80 characters appears in place in a multi-line display. Thus, if we imagine a screen containing this kind of "long" data being ported from DHCP to CHCS, we can see that the screen layout would have to be "blown up" to map data element to data element.

Further complicating the mapping possibilities, DHCP ScreenMan (Version 21) allows a multiple field to be handled in two different ways: either using a single display line, a la scrolling-mode:


with a pop-up window handling all the 'lower-level' information, or, alternatively, using a multiple-line display (multiple 'replications') within the 'upper-level' data:




Now, CHCS ScreenMan only uses this second, 'replicated' way of displaying multiples. Hence it is possible that a screen layout designed in DHCP would not fit into a CHCS screen, if it contained many multiples of the first type.

Moreover, DHCP allows the "scrolling multiples" to occupy only part of the width of the 80-column screen, whereas CHCS ScreenMan requires such scrolling to take place across the whole width of the display. In DHCP ScreenMan, therefore, Fields might appear to the right or left of a repeating multiple, as, for example --

Name: Select MULTIPLE: FIRST ID1 Height:

Sex: SECOND ID2 Weight:

Phone: THIRD ID3... BP:

where CHCS ScreenMan would not accommodate the equivalent layout.

Finally, and perhaps most annoyingly, whereas CHCS ScreenMan allows FileMan Word-Processing text Fields to be displayed along with other Fields on the same screen, DHCP requires that any Word-Processing Field text appear and be edited on its own screen (with its characteristic tab-and-margin ruler at the bottom). Obviously, this means that any display screens that include one or more Word-Processing Fields must look dramatically different in the two systems.

B. Features in DHCP ScreenMan not found in CHCS ScreenMan

The two packages differ in the way an 80-by-24 display is conceptualized. In CHCS, one such display corresponds to a "Screen", and there is thus in CHCS FileMan a File of SCREENS. In DHCP there is a File of FORMS, and each Form is conceptually broken down into PAGES, which are in turn broken down into BLOCKS, which are Entries in the Block File. A Block may correspond to an entire 80-by-24 display, or to just a part of one display. By adding the concept of a Block, DHCP ScreenMan allows for the ability to combine "sub-screens" easily in the design and construction of many displays that look somewhat alike.

Portability effect: Requires conversion. CHCS ScreenMan doesn't include the concept of a "Block". Therefore, any attempt to port DHCP screens into a CHCS system would need to include a mechanism to "flatten" DHCP Forms and Blocks into what CHCS ScreenMan simply calls Screens. Contrariwise, when CHCS screens are moved to DHCP, a converse mechanism would be required to create Blocks within Forms.

In the previous Section, we mentioned that DHCP FileMan Input Templates allow the Specifier ";REQ" to make a Field "required" for that Template, even if it is not "required" by its Data Dictionary definition. In the same way, a Field on a DHCP ScreenMan screen can be denoted as "required" only there. Again, CHCS does not provide for the equivalent design functionality.

Portability effect: Requires conversion. Again, we must judge that if a developer wants a data-entry event to be "required", he must have a reason for it. Therefore, conversion of a DHCP ScreenMan screen to CHCS would have to take into account any "Required" Fields. Within CHCS ScreenMan, though, we have a rough-and-ready way to try to mimic the "required" functionality: we can use some specially-programmed "Pre-filing logic" in the "CHK" node of the associated Input Template. This logic would look for the absence of entered values for the "required" Fields on the screen. If it found, for example, that Field 6 was blank and still needed to be entered, it would set the MUMPS variable "Y" equal to "6" and QUIT, which would return the user to the editing window for Field 6. The 'check logic', though, only happens at the end of all data entry, so it would not work exactly the same way as DHCP ScreenMan's "required" Fields do, where errors of omission are caught immediately.

A basic screen-design feature found in DHCP ScreenMan and not in CHCS is the so-called Form-only Field. This is a data-entry 'window' that can be defined only for the purpose of a specific Form (screen), and does not correspond to any permanent Field in any FileMan File. A simple example is a window that asks a YES/NO query like

Do you want to stop at this point:

Portability effect: SERIOUS. Since CHCS ScreenMan does not offer "form-only" fields, some workaround would be needed to port DHCP screens containing such fields into a CHCS environment. One distasteful way of doing this would be to add new Fields into the DataBase definition of the Files involved, at the CHCS end, just so that each such dummy Field could be used on a Screen.

Another DHCP ScreenMan feature never implemented in CHCS is the concept of a Display-only Block. DHCP developers can effectively use ScreenMan as a tool for simply building read-only output screens.

Portability effect: Requires conversion. No DHCP "Display-only" Block should ever be moved unmodified into a CHCS environment! Editing would there be allowed of data which the developer intended to be "seen but not touched". The conversion would require turning every Field on a Display-only Block into a Computed-Expression field in CHCS.

DHCP ScreenMan allows Field Captions (like "AGE:") to be "Executable", i.e., generated on-the-fly by MUMPS code. CHCS ScreenMan offers no equivalent.

Portability effect: Uncertain. It seems that this functionality would be seldom used. Nevertheless, if it were present in a DHCP screen (Block), it would be just possible to program a workaround in porting to CHCS. The workaround would probably involve code that actually did a MUMPS WRITE command to that place on the screen where the Caption was known to appear. Messy!

Although not directly related to application portability, it should be mentioned that the DHCP's characteristic boxed pop-up displays have a more sophisticated "look" than does CHCS Screenman. And for the designer of screens, the DHCP Form Editor is far more sophisticated than its CHCS equivalent, which essentially just turns a Word-Processed document, with Field "|WINDOWS|" in it, into a Screen sequence.

It's also worth noting that DHCP ScreenMan has a user keystroke functionality (not included in CHCS) that can significantly reduce user anxiety: the user can type "PF1-S" to "Save" permanently all data thus far entered, without leaving the screen-editing process.

Finally, the following Word-Processing functionalities are available to the DHCP ScreenMan user, and are not found in CHCS:

True Tab stops (CHCS merely lets the "TAB" key generate five spaces).

Delete from cursor to end of word (which also deletes the space at the end of the word!).

Move to end of line.

Status line toggle.

Wrap/nowrap toggle.

Switch back to scrolling-mode editing.

Again, these user features, per se, do not impact on the portability of screens. They are counterbalanced by the awkwardness of having to edit every Word-Processing text on a separate display screen, and having to hit more than a simple "return" to leave a blank text.

C. Features in CHCS ScreenMan not found in DHCP ScreenMan

Certainly the most significant feature of CHCS ScreenMan not available in DHCP is the basic ability to create a screen sequence from an existing FileMan Input Template. To see the advantage in this approach, consider a developer who needs to upgrade an existing "legacy" FileMan system to screen-oriented input. Using CHCS ScreenMan, he can simply name all the existing Input Templates that he wants to convert to screens, and, for each such Template, a first-pass screen sequence will automatically be built. In this process, ScreenMan assigns Field positions on the screens it builds using the Data Dictionary information about the maximum lengths of each Field value, and also obeys Template specification such as those pertaining to branching logic and alternative Field captions (e.g., NAME;"Patient Name"). After this speedy Template-to-Screen conversion, the developer can go into each Screen in turn, and start to refine the specification of where fields are placed on the screen, how many multiples are shown, etc. He does this by editing the Input Template associated with the Screen, because in CHCS, virtually all the information that specifies a screen sequence can be stored in the Input Template File. This interchangeability between Templates and screens allows many ScreenMan screens to be run, unmodified, as old-fashioned scrolling-mode Input Templates, in case the user happens to be at a terminal (e.g. a printer with keyboard) that cannot be used in screen mode. Indeed, at the higher level of package construction, CHCS developers put together input applications by referring to Input Templates (with MUMPS code calling "^DIE", just as in the old scrolling-mode days), rather than explicitly to Screen Sequences or "Forms".

Portability effect: SERIOUS. Not only does porting screens from DHCP to CHCS require the 'flattening' of screen design, as mentioned in Part B. of this Section, it also implies that a link must somehow be built from each DHCP "Form" to a brand-new CHCS Input Template -- a Template that wouldn't exist in the DHCP source! Porting from CHCS to DHCP, on the other hand would require somehow constructing explicitly the hierarchy of Blocks and Pages that is only implicit in CHCS screen design, while at the same time dropping the CHCS link between Input Templates and Screens.

A recent development at SAIC seems to offer some hope that this screen-conversion problem might be less troublesome in the future. In the most recent SAIC development version (called Version 26), an alternative screen-handler, often referred to as "WindowMan" is supplanting CHCS ScreenMan for application development. "WindowMan" has an internal structure much more similar to the DHCP tool, although it still lacks the distinction between "Blocks" and "Forms". Encouragingly, too, a rough "ScreenMan-to-WindowMan" translating tool has been written for internal use at SAIC (the "^DWUX" routine). The existence of this tool implies that the job of turning CHCS ScreenMan Templates into DHCP screens is at least partially susceptible to automation, although a programmer is needed to "tidy up" a lot of the converted Screens

In spite of the "WindowMan" development in CHCS, the layout problems presented above seem to indicate that any attempt to port screens from one system to the other would have to be done by developers "from scratch" by re-inputting screen designs in the target system. Complete automation of the process seems impracticable.

CHCS ScreenMan offers the developer a rarely-used ";B" Specifier on any Field, which makes the input "Blind". In operation, the user types an answer and does not see it, because character-echo is turned off within that one data window.

Portability effect: Requires conversion. This feature was obviously instituted because of a security concern that some password or confidential piece of data might be observed by someone else as it was typed. It is unlikely that this functionality would need to be carried over to the less-paranoid environment of

DHCP. If the equivalent were required, one might effect it by inserting "ECHO-OFF" MUMPS code into the "blind" Field's "Pre Action", and "ECHO-ON" code into the "Post Action". This workaround, of course, would have to be done carefully, to avoid Operating-System-dependence.

Although it does not impact so obviously on the conversion of applications from one system to the other, another distinctive feature of CHCS ScreenMan worth noting is that user keystrokes are associated with each functionality by tables, rather than being hard-coded. The tables can be customized by a non-programmer who understands ASCII. Thus, on the same CHCS computer at the same time, one user may be using "ESC" to signal the "abort" functionality, while another is using "PF1-Q". CHCS ScreenMan is thus easily customizable to a greater variety of terminals, including non-ANSI-Standard terminals such as QUMEs. As regards DHCP-CHCS interchange, note that, while one could construct within CHCS ScreenMan a table of keystrokes that would match what a DHCP user was familiar with (PF1-Q means "abort", and so on), a CHCS user migrating to DHCP would be required to learn DHCP's keystroke conventions.

Finally, we mention the following user functionalities, which are available in CHCS ScreenMan, and are not found in DHCP:

Move cursor to last window on screen.

Undo editing of current window or text line.

Print copy of screen to another device while in the middle of editing.

Spell-check while in the middle of Word-Processing.

Transfer text from another Entry, as in scrolling-mode Word-Processing.

Grab boilerplate text with a "window" code while in Word-Processing.

Again, these features are only noted for comparison purposes; their availablity does not directly relate to portability of screen-based applications. It must be said, though, that CHCS users, especially in areas like Radiology, have come to consider the availability of dynamic spell-checking an important feature of their "applications".