.dbf
 | |
| Filename extension |
.dbf |
|---|---|
| Internet media type | application/dbf, application/dbase |
| Developed by | dBase |
| Initial release | 1983 |
| Latest release | 7 |
| Website | dbase |
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
 | This section may require cleanup to meet Wikipedia's quality standards. The specific problem is: many version history entries with nothing to do with the file format. (February 2021) |
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 (Le
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.[4]
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.[5]
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,[6] which prevents creation of duplicate record numbers in the same table.
BDE version 5.1.0
Significant improvements over the prior releases.[7] There are also some limitations with regards to what the BDE can handle.[8]
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
| Byte | Contents | Meaning |
|---|---|---|
| 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 relative to 1900) |
| 4–7 | 32-bit number | Number of records in the database file |
| 8–9 | 16-bit number | Number of bytes in the header |
| 10–11 | 16-bit number | 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 |
- ^ The ISMARKEDO function checks this flag. BEGIN TRANSACTION sets it to 1, END TRANSACTION and ROLLBACK reset it to 0.
- ^ 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.
- ^ The maximum number of fields is 255.
- ^ 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
| Byte | Contents | Meaning |
|---|---|---|
| 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 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.[9]
| Extension | File content |
|---|---|
| .DBF | Database file |
| .DBK | Database backup file |
| .DBO | Command and procedure object file |
| .DBT | Database memo file |
| .DEF | Selector definition file |
| .DEM | Define statements for a CUA form |
| .DIF | Data Interchange Format, or VisiCalc file; used with APPEND FROM and COPY TO |
| .DOC | Documentation file; Applications Generator only |
| .ERR | Created if an error occurs during form generation, or if an unrecoverable error occurs |
| .FIL | Files list design object file |
| .EMO | Compiled format (.fmt) file |
| .FMT | Generated format file; from .scr file |
| .FNL | Report binary name list file |
| .FR3 | Renamed old dBASE HI report form (.frm) file |
| .ERG | Generated report form file; from .frm file |
| .FRM | Report form file |
| .FRO | Compiled report form (.ERG) file |
| .FW2, .FW3, .FW4 | Framework spreadsheet or database file; used for import and export |
| .GEN | Template file |
| .GRP | Windows group file for dBASE for DOS |
| .HLP | dBASE for DOS help files |
| .ICO | dBASE for DOS icon file under Windows |
| .INI | Windows-like INI file to save Label Designer and IDE state information. |
| .KEY | Keystroke macro library file |
| .LB3 | Renamed old dBASE III label form (.LBL) file |
| .LBG | Generated label form file; from .LBL file |
| .LBL | Label form file |
| .LBO | Compiled label form (.LBL) file |
| .LOG | Transaction log file |
| .LNL | Label binary name list file |
| .MBK | Multiple index backup file |
| .MDX | Multiple index file |
| .MEM | Memory file |
| .NDX | Single index file |
| .OVL | dBASE for DOS overlay file |
| PIF | Microsoft Windows file for non-Windows applications |
| .POP | Pop-up menu design object file; Applications Generator only |
| .PR2 | Printer driver file |
| .PRD | A file containing printer driver information for DBSETUP |
| .PRF | Print form file |
| .PRG | dBASE command or procedure file |
| .PRS | dBASE SQL command or procedure file |
| .PRT | Printer output file |
| .QBE | QBE query file |
| .QBO | Compiled QBE query (.QBE) file |
| .QRY | dBASE El query file |
| .RES | Resource file |
| .RPD | RapidFile file; used for import and export |
| .SC3 | Renamed old dBASE III screen (.SCR) file |
| .SCR | Screen file |
| .SNL | Screen binary name list file |
| .STR | Structure list design object file; Applications Generator only |
| .T44/.W44 | Intermediate work files; used by SORT and INDEX |
| .TBK | Database memo backup file |
| .TXT | ASCII text output file |
| .UPD | QBE update query file |
| .UPO | Compiled QBE update query (.UPD) file |
| .VAL | Values list design object file; Applications Generator only |
| .VMC | Configuration file; for Virtual Memory Manager (VMM) |
| .VUE | View file |
| .WIN | Logical window save file |
| .WKS, .WK1 | Lotus 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
- ^ Powell, David B. (1984-02-07). "From Basement To Boardroom". PC Magazine. p. 131. Retrieved 24 October 2013.
- ^ Powell, David B. (1984-02-07). "From Basement to Boardroom". PC Magazine: 131–135. Retrieved 2014-08-15.
- ^ "dBASE Table File Format (DBF)". Digitalpreservation.gov. Retrieved 2014-08-15.
- ^ Bachmann, Erik. "Xbase Data file (*.dbf)". www.clicketyclick.dk.
- ^ "dBASE .DBF File Structure". Dbase.com. Retrieved 2014-08-15.
- ^ Jean-Pierre Martel. "AutoIncrement Fields". Dbase.com. Retrieved 2014-08-15.
- ^ Jean-Pierre Martel. "New BDE 5.1.0 and Visual dBASE 7.01". Dbase.com. Retrieved 2014-08-15.
- ^ [1]
- ^ "dBASE Classic". dBASE Classic. Retrieved 2014-08-15.
Further reading
- Ben Fry (18 December 2007). Visualizing Data: Exploring and Explaining Data with the Processing Environment. p. 325. ISBN 9780596554729.
- Allen Kent, James G. Williams (5 October 1989). Encyclopedia of Microcomputers: Volume 4 - Computer-Related Applications: Computational Linguistics to dBase. p. 398. ISBN 9780824727031.
External links
- FoxBase, dBASE III/IV file format specification (retrieved 6 August 2018)