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The Devil is in the File Types
by Gary B. Hoffman

In my last column, Sharing Genealogy Files, I discussed the issue of transferring genealogical information from one program to another. Some programs can read the files created by others and most programs can read and write an intermediate file type called GEDCOM. Many people who read that column e-mailed me with particular questions about different file types they'd encountered. Most had received a file and didn't know how to convert it. As a general rule, it's easier to convert the file on the sending end than on the receiving end. That is, the sender should take responsibility for giving the receiver a file that the receiver can use.

Still, I wanted to be able to identify an originating program from a given file name and file extension. So I asked Lance Dohe, current president of the Computer Genealogy Society of San Diego, to dig up all the file types for the many genealogy programs he has installed on his computers. As a result of Lance's research, I can now make a good guess about the program that belongs to a particular file. I'll share our list with you in the table below (alphabetized by program name).

First, some background on file types. A file type is a merely a part of the name of a file that extends to the right of the period, or dot. The practice of using a file name extension actually preceded MS-DOS, where it is optional. Most computer users know that DOS file names can be up to eight characters in length and may have a three character file extension after a period, which acts as a separator, such as "ARTICLE.TXT". But while DOS doesn't really care about file extensions, programs do. WordPerfect for DOS, for example, looked for files that had an extension of .WP5 and opened them as its own. Lotus 1-2-3 wanted .WKS files, and so on. Subsequent versions of the programs used variations of the file type, such as .WK1, .WK2, etc.

November 11, 1998

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Windows introduced the idea of associations. A small database inside Windows keeps track of file extensions and which programs they correspond to. This allows you to double-click on a file and automatically trigger Windows to start the correct program. Windows also shows you an icon for a file depending on its associated file type.

Of course, Macintosh users are familiar with these actions. On a Mac, all files have both a four-character file type as well as a four-character "creator" which aren't part of the file names but are hidden attributes of the files. The Mac's Finder program keeps track of file types, creators, and icons in the Desktop Database, a hidden file. Sometimes the desktop database gets corrupted and files don't open their parent program. That's when Mac users need to rebuild the desktop by holding down the Apple-option keys while rebooting.

Beginning with Windows 95, the file type extension on a PC is normally hidden for types that Windows can associate with a program. When programs ask for a file name, they automatically assign a file type and Windows hides it from you in most views of files in a directory. To see the file extensions, you can either select the Properties of a file or go to the Views menu of a particular directory and de-select the option to hide file types.

Because Windows now hides file extensions in most views, users are becoming less aware of the file type designations for the programs they use. The list below is offered as a guide only, and is by no means exhaustive. I welcome additions and corrections so that I can publish a more comprehensive guide to genealogy file types in the future. Nonetheless, it's a good indication of what you may run into when someone sends you a genealogy file.

To help me build this table of file types, Lance Dohe examined files associated with each of the listed genealogy programs. In most cases, we located all the files necessary to display one family database. The asterisk (or "star") indicates where a file name varies either by user command or program operation. For some programs, the name portion is constant and the extension varies.


Because Windows now hides file extensions in most views, users are becoming less aware of the file type designations for the programs they use.

Program (version)

Number of files, file extensions

Ancestral Quest (PAF 2.31 compatible) 7 *.DAT files
Brother's Keeper (5.x for Windows) 6 or 7 *.DT5 files; possibly 1 *.TXT file and 1 or more *.DTA files
Corel Family Tree 5 *.TPS files
Cumberland Family Tree 25 files, a mixture of *.DAT and *.KO1
Family Origins for Windows 30 or more data files with no apparent order
Family Records (4.x) up to 33 files, but generally:
18 TEMPLATE.* (extension varies)
1 CONFIG4.DAT configuration file
perhaps 4 NAMELIST.* (extension varies)
Family Ties 1 *.IFT file
Family Tree Maker (2.0 - 4.0 for DOS) 1 *.FTM file
Family Tree Maker (2.0 - 5.0 for Windows) 1 *.FTW file (the only required file)
1 backup data file, *.FBK
possibly 1 compressed backup file, *.FBC
Personal Ancestral File (PAF 3.0) 2 files, *.LST and *.PAF
Parents 10 files, 5 *.DB and 5 *.IDX
ROOTS4 about 10 files, a mixture of *.CDX, *.DBF, and *.FPT
The Master Genealogist (3.x for Windows) 36 - 46 files, a mixture of *.CDX, *.DBF, *.FPT
Ultimate Family Tree about 30 files, a mixture of *.CDX, *.DBF, *.FPT

About the Author

Gary Hoffman has been involved in genealogy research for over 30 years. He is former president of the Computer Genealogy Society of San Diego and is CGSSD's Webmaster. Currently a computer manager at the University of California's San Diego campus, he recently received a law degree and passed the California bar exam. His articles on technical and legal issues relating to genealogy have appeared in several online publications and newsletters and he is a regular speaker at national genealogy conferences.


Copyright © 1998 by Gary B. Hoffman. All Rights Reserved. Any republication of this article requires the express consent of the author.

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