Miller columns are a browsing/visualization technique that can be applied to tree structures. The columns allow multiple levels of the hierarchy to be open at once, and provide a visual representation of the current location. It is closely related to techniques used earlier in the Smalltalk browser, but was independently invented by Mark S. Miller in 1980 at Yale University. The technique was then used at Project Xanadu, Datapoint, and NeXT.
While at Datapoint, Miller generalized the technique to browse directed graphs with labeled nodes and directed graphs with labeled nodes and arcs. In all cases, the technique is appropriate only for structures with high degree (large fanout). For low-degree structures, outline editors or graph viewers are more effective.
Miller columns are most well known today as the “Columns view” mode of the Mac OS X Finder, as well as the "Browser" view in iTunes. The columns in Finder descend directly from the NeXTSTEP File Viewer's use of Miller columns going back to 1986. The GNUstep project continues to offer a Miller column browser that closely follows the NeXT approach, bringing the advantages of a Column browser to Linux, BSD, and other operating systems with large tree structures. The iPod's browsing of categories and audio file tag attributes is reminiscent of column browsing, but only one column is visible at a time.
Many software music players implement a "tag browsing" feature that utilizes Miller columns.
Miller columns have several issues from usability standpoint:
- Requirement for horizontal scrollbars when displaying deeper folder structures
- Relationship between columns is unclear
- Usability issues for touchscreen users
Touchscreen usability issues for Miller columns are related to creation of new columns under the user's hand while navigating data structures.
Use in file browsers
- Finder, the default file browser on Mac OS X, uses Miller columns in its "Columns" view.
- Path Finder is a shareware file browser for Mac OS X supporting Miller column view amongst others.
- GWorkspace, a workspace manager for GNUstep which can be used as file browser, uses Miller columns.
- ranger, a terminal-based file browser with Vi-like key bindings, uses a multi-column mode similar to Miller columns.
- evidence, an apparently obsolete file browser for Enlightenment, used Miller columns in its “browser-view”.
- Thunar, the default file browser for Xfce, used to have a branch called “columns-view” which was given up later.
- Dolphin, the default file browser of KDE, also canceled the further development of Miller columns due to too complex source code making it hard to maintain.
- Tkdesk, a file browser for the X Window System, uses Miller columns.
- Marlin is a file browser written in GTK 3 which implements Miller columns.
- Pantheon Files (or just Files, for short) is a fork of Marlin actively developed by the Elementary team.
- Nautilus, the official file browser for the GNOME desktop, still discusses the necessity of Miller columns while numerous users demand it.
- FSViewer is an obsolete file browser for GNU Window Maker using Miller columns.
- Greg's Browser is an obsolete, NeXT-inspired column browser for the Mac OS that predates Mac OS X.
- WinBrowser and Ultraexplorer are a file browsers for Microsoft Windows supporting Miller columns.
- One Commander is a file browsers for Microsoft Windows using automatically scaled Miller columns in tabbed interface.
- Shelf: NeXT GUI element that can be combined with columns to make a file manager.
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