DN line - breakthrough in VFS by Nikolai Bezroukov

The DOS Navigator (DN) is an extremely interesting and influential implementation of OFM. I discover DN existence rather late and the first version that I checked was version 1.5 released in April 1997. But analyses of previous versions and correspondence with one of the authors suggest the DN was the leader since early 1993 (from version 1.10). By implementing three additional VFS DN opened a new generation of OFMs. It should be considered as an ultimate DOS-based classic implementation of OFM and it is difficult to compete with DN featurewise. It was distributed as shareware and not all features were available for unregistered users.

Like MC it is a team effort under the leadership of Stefan Tarnukov. The initial version of DN I (v 0.90) was released in 1991 and written by Stefan Tanurkov, Andrew Zabolotny and Sergey Melnik (all from Kishinev, Moldavia). After that DN was rewritten using TurboVision by Stefan Tanurkov and Dmitry Dotsenko (currently in Moscow State University). This versions are sometimes referred as DN II. DN II was actively developed till the beginning of 1995 (until the version 1.35 that should be considered as a milestone in the OFM implementations). After the development mostly took bugfixing direction. So most material below is applicable to v.1.35 although I did not test it.

Several other programmers participated in the development on that stage: after v. 1.37 Slava Filimonov (he is now an author of the MRP Navigator - a file shell, designed for use for Win95/NT) and Ilya Bagdasarov were in charge for bug fixing. The version 1.5 was authored by Stefan Tanurkov and Max Masyutin.

Although it is a text based, DN seems to be more close to GUI-based OFM counterparts as it is using Borland Turbo Vision for the interface implementation. The size of DN distribution is also more close to GUI-based OFMs (1M). Although it seems to be a little bit overloaded with additional utilities, the core OFM functionality is really impressive.

Disclaimer: The author has a very limited experience working with DN and tested only the demo of v .150. The demo does not provide some advanced features. In this case documentation was used.

DN Contributions

DN 1.35 should be considered as a milestone in the OFMs virtual file system implementations. It had made a very important contributions in this area. The feature set and flexibility of DN in this area are really amazing. Among a long list of DN innovations I would like to single out the following three VFS:

Xtree VFS -- the ability to view a directory with all subdirectories as a single virtual directory. Drive a directory can then be viewed as a flat list of files. This idea was pioneered in Xtree file manager and is a natural and very important extension of the OFM paradigm. Filters on subtree are essentially a search function for subtree and in future implementations this two functions should be merged.

Briefcase VFS that links to files and directories on existing drives into single virtual directory(or drive). Semantically it is an implementation of the link operation in UNIX, so a briefcase should be a standard feature in all UNIX implementations of OFMs. It is possible to copy files from different directories to the briefcase drive and then work with this links as if they are were stored on this drive. All file operations are supported. Of course implementation of briefcase on a regular FAT file system is not as simple as in UNIX, but this is a Microsoft fault ;-). For drives on some versions of MS DOS and all version of PC DOS join operation was available (strange mix of link and mount operations), so limited capability of creating briefcase was present even in DOS.

List-based VFS - the panel will show only files that are results of the search for the files, that are present in the text-file list. This is a very important generalization of the find file function and panel filters. Panel filters as currently implemented are not very useful. In DN the user activates list-based VFS using Panel|Read. After getting the name of the file with the list DN will read the list, for example files.bbs, and search for file present in the list. Much better way of implementing this feature is generalization of panel filters. One need just to add the capability to read the specification of the filter from the file and to apply the filter to subtreee rather than single directory. The panel will display the list of files found. In DN files can be not only in different directories, but on different drives and that possibility should be preserved. Here we see a difference between this VFS and Flat subtree VFS although they are somewhat similar and definitely can share considerable part of the implementation code. Again I would like to stress that OFM implementers just need to generalize filters to have this feature - an old concept can be extended into new domain.

This three new types of VFS are really a milestone in OFM development. The Xtree VFS is an important productivity enhancement tool. It was first introduced in Xtree (as early as in 1987) and this capability probably was the single most important reason of XTree popularity. As a limited implementation of Xtree VFS exists in NC 5.0 this VFS should be a standard in all modern OFMs. It provides really superior functionality to any known to me Windows-style file manager. With Xtree-line of file managers discontinued (by the way by Symantec :-(), it can became a distinctive mark of OFMs.

Three other innovations are also very important:

The ability to have several sets of panels and switch between them like in a real multi-windows editor. Usefulness of the ability to have several sets of panels is proved by attempts by other authors to add similar features to OFM (for example early attempts to introduce 4 panels in the PIE Commander by Valentin Chernyak) and experience with Windows-style file managers where multiple windows are a standard feature.
DN was probably the first OFM implementation that introduced keyboard macrorecoder in OFMs. DN permits to record a key sequence and replay it.
History lists for directory visited, selection masks, etc.

As I already mentioned DN introduced many other innovations. Among them:

The first correct implementation of the panel information window concept. Lines in the panel information windows are customizable via file manager options menu. Default information windows in DN is a three line entity with a current file as the first line, the number of selected files is the second and number of files in the directory in the third line.
According to Max Masyutin additional macro variables have existed in DN since 1991, i.e. they has been implemented earlier that in VC.
Several color styles that can be assigned to groups of extensions (file groups are provided by default).
Movable panel delimiter can make the panels asymmetric so that one can view descriptions and additional columns on the single panel.
Custom video modes (30-line panel view implementation).
Drag and drop implementation for groups of files and single files (from information window) !
Compare directories operation (permits comparing contents);
Collapsible tree views (although I did not find the key to return to regular tree view);
Directory tree has expand/collapse options:

+ : Expands/reads the tree starting at the current directory for one subdirectory level
- : Collapse the subdirectory tree below the current directory.
* : Expands/reads all subdirectories starting at the current directory.

Persistent command history as an option
Advanced file search:

List of selection masks (e.g. *.bak; *.$$$; *.tmp ),
Find words.
Search inside archives.
Find file not older that N days.
Persistent history for search.
FileFind operation in DN can work in background.

Some(limited) steps toward mask-selection language. DN does not use UNIX style regular expressions, but there is an option of negating the mask in the selection panel. Also there is a "mask construction windows" that can be displayed using Alt-Del. It seems to be somewhat similar to the Foxpro expression construction windows and permits constructing expression from several masks use negation for any single mask (JC solution seems to be simpler and more flexible, see below).
Alt key activated top menu like in VC.
Additional operations on selection lists.

The ability to select files with the same name (Alt-Grey+);
with the same extension (Ctrl-Shift-Gray+)
with the same type (executable, etc) as the current file.
the ability to select all file irregarding the file mask
The ability to select all files irregarding the file mask

The list of disks are displayed as the last line of information windows and there is an ability to switch from one disk to another by just clicking the disk letter with mouse (It is also possible to select next disk using Ctrl-Left/Right but I see no benefits from such an operation).
Translation tables for built-in viewer (but there is no possibility to omit certain characters as in UFO).
Operations with floppy images;
The ability to edit commands history;
New keys for selection of all files irregarding current selection mask, selecting all files with extension equal to the extension of the file under cursor, etc.

Viewer has several interesting features:

Build-in calculator
dump mode (with address button)
Filter of ASCII characters

The built-in editor in DN is pretty decent, but without any macro facilities. IMHO for OFMs unless the editor is programmable and serve as a base of OFM implementation it probably should belong to QE class (QE or Quick Edit is one of the most famous DOS-based editor programmed in assembler - a lot of power in 32K of code) or even less. From that point of view the syntax highlighting is probably an overkill for the light-weight build-in editor as well as line drawing; an alternative (external) middle-weight or heavyweight editor should be used in complex cases. Among useful thing that can be implemented without much trouble I would like to mention:

ASCII table;
Jump operation;
Two types of blocks (line blocks and stream blocks);
Insert Date and Time opeartion;
Change case command (for words and blocks).