.dbf
Filename extension
.dbf
Internet media typeapplication/dbf, application/dbase
Developed bydBase
Initial release1983 (1983)
Latest release
7
Websitedbase.com

The .dbf file extension represents the dBase database file. The file type was introduced in 1983 with dBASE II. The file structure has evolved to include many features and capabilities. Several additional file types have been added, to support data storage and manipulation. The current .dbf file level is called Level 7. The .dbf format is supported by a number of database products.

Overview

The original dBASE database was known as Project Vulcan and was started by Wayne Ratliff in 1978. At the time the file that held the data was a simple table that could have data added, modified, deleted, or printed using the ASCII characters set.[1] As the product became more popular, the underlying file type .dbf was expanded, and additional files were added to increase the capabilities of the database system. Despite dBASE being an IDE (integrated development environment), a database system, a compiler, and a database application builder, the original .dbf file was still used for the actual data storage mechanism.

History of the file format

Classical .dbf

Project Vulcan – CP/M (Level 1)
There is no publicly available information on the original layout. What is known is that it was a simple table which allowed adding, deleting, modifying, and outputting ASCII data. It was written for 8-bit machines that ran CP/M.
dBASE II – MS-DOS (Level 2)
dBASE II was the first major release by Ashton-Tate. It had many advancements beyond the simple table structures of Project Vulcan.[2]
  • Still written for 8-bit computing
  • Increased the number of fields from 16 to 32
  • Introduced a SORT routine
  • 16-bit version finally released in April 1983 (version 2.4)
dBASE III – MSDOS (Level 2sh)
dBASE III (version "1.0"), was released in June 1984. This was a fully 16-bit application. dBASE III's file format is a transitional step between dBASE II and dBASE III+.

Modern dBASE

dBASE III+ – MS-DOS (Level 3)
dBASE III+ was released in December 1985. It ushered the modern dBASE file format. It is incompatible with dBASE III's file format.[3]
dBASE IV – MS-DOS (Level 4)
  • 1.0 x322 Oct 1988
  • 1.0 x55 Mar 1993 – dBASE Compiler
  • 2.0 x12 Oct 1993 Includes fixes in dBASE IV v2.0 x16 above (not x17 i.e. not VLM compatible, dB5D exe's are compatible). It's also a new version that contain new features not in the V1.0 product:
    • 32-bit generation
    • Auto compiling and linking
    • Smaller .EXE size
    • Menu-driven user interface
    • Linker can produce combined .DBO output
    • Linker can produce a .MAP file
    • Compiler supports alternate date formats
    • command-line switches accept wildcards in file names.
dBASE V – MS-DOS (Level 5)
1.0 x46 Jun 1994
BDE – Borland Database Engine 2.52

This was the last update to the 16-bit version of the Borland Database Engine (BDE).[4]

dBASE V – MS-Windows (Level 5)

  • 5.5 b673 Jul 1995

xBase

xBase is a name applied to clones of the dBase, typically dBASE III+–V. Most xBase programs either use the format directly or uses a derived format with custom extensions. Erik Bachmann maintains an open-licensed description of these formats.[5]

dBASE 7

The Level 7 structure is the latest supported by dBASE and BDE. It is incompatible with the previous file format, and is supported by few third-party applications.[6]

dBASE 7 – MS-Windows (Level 7)

  • 7.0 b1345 Dec 1997 Full 32 bit version for Win 95/NT

Level 7 brought many improvements. The maximum length for field names increased from 10 to 31 characters. Some new fields types were added, such as the auto-increment field,[7] which prevents creation of duplicate record numbers in the same table.

BDE version 5.1.0

Significant improvements over the prior releases.[8] There are also some limitations with regards to what the BDE can handle.[9]

File format of Level 5 DOS dBASE

The "modern dBASE" III+–V is the most common dBASE file format found in the wild. In "modern dBASE", a .dbf file consists of a header, the data records, and the end-of-file marker.

  • The header contains information about the file, such as the number of records and the number of types of fields used in the records.
  • The records contain the actual data.
  • The end of the file is marked by a single byte, with value 0x1A.

File header

Layout of file header in dBase level 5
ByteContentsMeaning
0 1 byte Valid dBASE for DOS file; bits 0–2 indicate version number, bit 3 indicates the presence of a dBASE for DOS memo file, bits 4–6 indicate the presence of a SQL table, bit 7 indicates the presence of any memo file (either dBASE m PLUS or dBASE for DOS)
1–3 3 bytes Date of last update; formatted as YYMMDD (with YY being the number of years since 1900)
4–7 4 bytes (LE) Number of records in the database file
8–9 2 bytes (LE) Number of bytes in the header
10–11 2 bytes (LE) Number of bytes in the record
12–13 2 bytes Reserved; fill with 0
14 1 byte Flag indicating incomplete transaction[note 1]
15 1 byte Encryption flag[note 2]
16–27 12 bytes Reserved for dBASE for DOS in a multi-user environment
28 1 byte Production .mdx file flag; 1 if there is a production .mdx file, 0 if not
29 1 byte Language driver ID
30–31 2 bytes Reserved; fill with 0
32–n [note 3][note 4] 32 bytes each array of field descriptors (see below for layout of descriptors)
n + 1 1 byte 0x0D as the field descriptor array terminator
  1. ↑ The ISMARKEDO function checks this flag. BEGIN TRANSACTION sets it to 1, END TRANSACTION and ROLLBACK reset it to 0.
  2. ↑ If this flag is set to 1, the message Database encrypted appears. Changing this flag to 0 removes the message, but does not decrypt the file.
  3. ↑ The maximum number of fields is 255.
  4. ↑ n means the last byte in the field descriptor array. The array's size depends on the number of fields used in a database. n is equal to 31 + 32 * (number of fields).

Field descriptor array

Layout of field descriptors in dBase level 5 (used inside the file header)
ByteContentsMeaning
0–10 11 bytes Field name in ASCII (zero-filled)
11 1 byte Field type. Allowed values: C, D, F, L, M, or N (see next table for meanings)
12–15 4 bytes Reserved
16 1 byte Field length in binary (maximum 254 (0xFE)).
17 1 byte Field decimal count in binary
18–19 2 bytes Work area ID
20 1 byte Example
21–30 10 bytes Reserved
31 1 byte Production MDX field flag; 1 if field has an index tag in the production MDX file, 0 if not

    Database records

    Each record begins with a 1-byte "deletion" flag. The byte's value is a space (0x20), if the record is active, or an asterisk (0x2A), if the record is deleted. Fields are packed into records without field separators or record terminators.

    All field data is ASCII. Depending on the field's type, the application imposes further restrictions:

    Field types in dBase level 5
    Field type Mnemonic What it accepts
    C Character Any ASCII text (padded with spaces up to the field's length)
    D Date Numbers and a character to separate month, day, and year (stored internally as 8 digits in YYYYMMDD format)
    F Floating point -, ., 0–9 (right justified, padded with whitespaces)
    L Logical Y, y, N, n, T, t, F, f, or ? (when uninitialized)
    M Memo Any ASCII text (stored internally as 10 digits representing a .dbt block number, right justified, padded with whitespaces)
    N Numeric -, ., 0–9 (right justified, padded with whitespaces)

    Memo fields and the .DBT file

    A memo (.DBT) file consists of blocks numbered sequentially (0,1,2, and so on). SET BLOCKSIZE determines the size of each block. The first block, block 0, is the memo file header.

    Each memo field of each record in the .DBF file contains the number of the block (in ASCII) where the memo field begins. If the memo field contains no data, the .DBF file contains blanks (0x20) rather than a number.

    When a memo field's content changes, its block number may also change. I.e. the memo gets relocated. In that case, the number in the .DBF file gets updated.

    In dBASE III PLUS, the space consumed by deleted text in a memo field cannot be reused — the .DBT file size grows each time text is added, even if other text has been deleted. dBASE for DOS may reuse that space for new text. dBASE IQ PLUS always appended new text to the end of the .dbt file.

    Other file types found in dBASE

    dBASE defines many types of files. It also recognizes some operating system files and files from other products. The table below lists the most commonly used formats first. It was compiled from the documentation of dBASE III+, dBASE IV, and dBASE CLASSIC.[10]

    File types recognized by dBASE, up to dBASE CLASSIC
    ExtensionFile content
    .DBFDatabase file
    .DBKDatabase backup file
    .DBOCommand and procedure object file
    .DBTDatabase memo file
    .DEFSelector definition file
    .DEMDefine statements for a CUA form
    .DIFData Interchange Format, or VisiCalc file; used with APPEND FROM and COPY TO
    .DOCDocumentation file; Applications Generator only
    .ERRCreated if an error occurs during form generation, or if an unrecoverable error occurs
    .FILFiles list design object file
    .EMOCompiled format (.fmt) file
    .FMTGenerated format file; from .scr file
    .FNLReport binary name list file
    .FR3Renamed old dBASE HI report form (.frm) file
    .ERGGenerated report form file; from .frm file
    .FRMReport form file
    .FROCompiled report form (.ERG) file
    .FW2, .FW3, .FW4Framework spreadsheet or database file; used for import and export
    .GENTemplate file
    .GRPWindows group file for dBASE for DOS
    .HLPdBASE for DOS help files
    .ICOdBASE for DOS icon file under Windows
    .INIWindows-like INI file to save Label Designer and IDE state information.
    .KEYKeystroke macro library file
    .LB3Renamed old dBASE III label form (.LBL) file
    .LBGGenerated label form file; from .LBL file
    .LBLLabel form file
    .LBOCompiled label form (.LBL) file
    .LOGTransaction log file
    .LNLLabel binary name list file
    .MBKMultiple index backup file
    .MDXMultiple index file
    .MEMMemory file
    .NDXSingle index file
    .OVLdBASE for DOS overlay file
    PIFMicrosoft Windows file for non-Windows applications
    .POPPop-up menu design object file; Applications Generator only
    .PR2Printer driver file
    .PRDA file containing printer driver information for DBSETUP
    .PRFPrint form file
    .PRGdBASE command or procedure file
    .PRSdBASE SQL command or procedure file
    .PRTPrinter output file
    .QBEQBE query file
    .QBOCompiled QBE query (.QBE) file
    .QRYdBASE El query file
    .RESResource file
    .RPDRapidFile file; used for import and export
    .SC3Renamed old dBASE III screen (.SCR) file
    .SCRScreen file
    .SNLScreen binary name list file
    .STRStructure list design object file; Applications Generator only
    .T44/.W44Intermediate work files; used by SORT and INDEX
    .TBKDatabase memo backup file
    .TXTASCII text output file
    .UPDQBE update query file
    .UPOCompiled QBE update query (.UPD) file
    .VALValues list design object file; Applications Generator only
    .VMCConfiguration file; for Virtual Memory Manager (VMM)
    .VUEView file
    .WINLogical window save file
    .WKS, .WK1Lotus 1-2-3 file; used with APPEND FROM and COPY TO

    See also

    • Clipper – Compiler for xBase
    • File format – Structure of information stored on a computer
    • FoxBASE – Programming language

    References

    1. ↑ Powell, David B. (1984-02-07). "From Basement To Boardroom". PC Magazine. p. 131. Retrieved 24 October 2013.
    2. ↑ Powell, David B. (1984-02-07). "From Basement to Boardroom". PC Magazine: 131–135. Retrieved 2014-08-15.
    3. ↑ "dBASE Table File Format (DBF)". Digitalpreservation.gov. 8 October 2012. Retrieved 2014-08-15.
    4. ↑ "dBASE Documentation Download - dBase, LLC". Dbase.com. Retrieved 2014-08-15.
    5. ↑ Bachmann, Erik. "Xbase Data file (*.dbf)". www.clicketyclick.dk.
    6. ↑ "dBASE .DBF File Structure". Dbase.com. Retrieved 2014-08-15.
    7. ↑ Jean-Pierre Martel. "AutoIncrement Fields". Dbase.com. Retrieved 2014-08-15.
    8. ↑ Jean-Pierre Martel. "New BDE 5.1.0 and Visual dBASE 7.01". Dbase.com. Retrieved 2014-08-15.
    9. ↑ "DBase Plus Help 8".
    10. ↑ "dBASE Classic". dBASE Classic. Retrieved 2014-08-15.

    Further reading

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