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Data File Header Structure for the dBASE Version 7 Table File

Data File Header Structure for the dBASE Version 7 Table File


Note: Unless prefaced by "0x", all numbers specified in the Description column of the following tables are decimal.

1.1 Table File Header

Byte Contents
Description
0 1 byte Valid dBASE for Windows table file, bits 0-2 indicate version number: 3 for dBASE Level 5, 4 for dBASE Level 7.

Bit 3 and bit 7 indicate presence of a dBASE IV or dBASE for Windows memo file; bits 4-6 indicate the presence of a dBASE IV SQL table; bit 7 indicates the presence of any .DBT memo file (either a dBASE III PLUS type or a dBASE IV or dBASE for Windows memo file).

1-3 3 bytes Date of last update; in YYMMDD format.  Each byte contains the number as a binary.  YY is added to a base of 1900 decimal to determine the actual year. Therefore, YY has possible values from 0x00-0xFF, which allows for a range from 1900-2155.
4-7 32-bit number Number of records in the table. (Least significant byte first.)
8-9 16-bit number Number of bytes in the header. (Least significant byte first.)
10-11 16-bit number Number of bytes in the record. (Least significant byte first.)
12-13 2 bytes Reserved; filled with zeros.
14 1 byte Flag indicating incomplete dBASE IV transaction.
15 1 byte dBASE IV encryption flag.
16-27 12 bytes Reserved for multi-user processing.
28 1 byte Production MDX flag; 0x01 if a production .MDX file exists for this table; 0x00 if no .MDX file exists.
29 1 byte Language driver ID.
30-31 2 bytes Reserved; filled with zeros.
32-63 32 bytes Language driver name.
64-67 4 bytes Reserved.
68-n 48 bytes each Field Descriptor Array (see 1.2).
n+1 1 byte 0x0D stored as the Field Descriptor terminator.
n+2 See below for 
calculations of size
Field Properties Structure

n above is the last byte in the field descriptor array. The size of the array depends on the number of fields in the table file.

1. 2 Field Descriptor Array

(One for each field in the table)

Byte Contents
Description
0-31 32 bytes Field name in ASCII (zero-filled).
32 1 byte Field type in ASCII (B, C, D, N, L, M, @, I, +, F, 0 or G).
33 1 byte Field length in binary.
34 1 byte Field decimal count in binary.
35-36 2 bytes Reserved.
37 1 byte Production .MDX field flag; 0x01 if field has an index tag in the production .MDX file; 0x00 if the field is not indexed.
38-39 2 bytes Reserved.
40-43 4 bytes Next Autoincrement value, if the Field type is Autoincrement, 0x00 otherwise.
44-47 4 bytes Reserved.

1.3 Field Properties Structure

This contains a header describing the Field Properties array, followed by the actual array, followed by property data. It is contained in the .DBF header and comes immediately after the Field Descriptor terminator (See Table 1.1).  

Byte Contents
Description
0-1 16-bit number Number of Standard Properties. 
2-3 16-bit number Start of Standard Property Descriptor Array. (see 1.3.1 )
4-5 16-bit number Number of Custom Properties. 
6-7 16-bit number Start of Custom Property Descriptor Array. (see 1.3.2 )
8-9 16-bit number Number of Referential Integrity (RI) properties.
10-11 16-bit number Start of RI Property Descriptor Array. (see 1.3.3 ) 
12-13 16-bit number Start of data - this points past the Descriptor arrays to data used by the arrays - for example Custom property names are stored here.
14-15 16-bit number Actual size of structure, including data (Note: in the .DBF this will be padded with zeroes to the nearest 0x200, and may have 0x1A at the end). If the structure contains RI data, it will not be padded.
16-n 15 bytes each Standard Property Descriptor Array (n = (15*number of standard properties) + 16). (see 1.3.1)
(n+1)-m 14 bytes each Custom Property Descriptor Array (m = n+ 14*number of custom properties). (see 1.3.2)
(m+1)-o 22 bytes each RI Property Descriptor Array (o = m+ 22*number of RI properties). (see 1.3.3)

1.3.1 Standard Property and Constraint Descriptor Array

Byte Contents
Description
0-1 16-bit number Generational number. More than one value may exist for a property. The current value is the value with the highest generational number.
2-3 16-bit number Table field offset - base one. 01 for the first field in the table, 02 for the second field, etc. Note: this will be 0 in the case of a constraint.
4 8-bit number Which property is described in this record:
01 Required

02 Min

03 Max

04 Default 

06 Database constraint
5 1 byte Field Type:
00 No type - constraint

01 Char

02 Numeric

03 Memo

04 Logical 

05 Date

06 Float

08 OLE

09 Binary

11 Long

12 Timestamp

13 Double

14 AutoIncrement (not settable from the Inspector)
6 1 byte 0x00 if the array element is a constraint, 0x02 otherwise.
7-10 4 bytes Reserved
11-12 16-bit number Offset from the start of this structure to the data for the property. The Required property has no data associated with it, so it is always 0. 
13-14 16-bit number Width of database field associated with the property, and hence size of the data (includes 0 terminator in the case of a constraint).

1.3.2 Custom Property Descriptor Array

Byte Contents Description
0-1 16-bit number Generational number. More than one value may exist for a property. The current value is the value with the highest generational number. 
2-3 16-bit number Table field offset - base one.  01 for the first field in the table, 02 for the second field, etc.
4 1 byte Field Type 
01 Char

02 Numeric

03 Memo

04 Logical 

05 Date

06 Float

08 OLE

09 Binary

11 Long

12 Timestamp

13 Double

14 AutoIncrement (not settable from the Inspector)
5 1 byte Reserved
6-7 16-bit number Offset from the start of this structure to the Custom property name.
8-9 16-bit number Length of the Custom property name.
10-11 16-bit number Offset from the start of this structure to the Custom property data.
12-13 16-bit number Length of the Custom property data (does not include null terminator).

1.3.3 Referential Integrity Property Descriptor Array

Byte Contents Description
0 8-bit number 0x07 if Master (parent), 0x08 if Dependent (child). 
1-2 16-bit number Sequential number, 1 based counting. If this number is 0, this RI rule has been dropped.
3-4 16-bit number Offset of the RI rule name - 0 terminated.
5-6 16-bit number Size of previous value.
7-8 16-bit number Offset of the name of the Foreign Table - 0 terminated.
9-10 16-bit number Size of previous value.
11 1 byte Update & delete behaviour:
Update Cascade 0x10

Delete Cascade 0x01
12-13 16-bit number Number of fields in the linking key.
14-15 16-bit number Offset of the Local Table tag name - 0 terminated.
16-17 16-bit number Size of previous value.
18-19 16-bit number Offset of the Foreign Table tag name - 0 terminated.
20-21 16-bit number Size of previous value.

(Foreign = in the other table,  Local = in this table)

Property Data

For standard properties, everything is stored exactly as it is in the Table records. Custom property data is stored as the Name string, followed immediately by the Value string, and a null terminator. The Constraint text is stored as a null-terminated string.

Table Records

The records follow the header in the table file. Data records are preceded by one byte, that is, a space (0x20) if the record is not deleted, an asterisk (0x2A) if the record is deleted. Fields are packed into records without field separators or record terminators. The end of the file is marked by a single byte, with the end-of-file marker, an OEM code page character value of 26 (0x1A).

Storage of dBASE Data Types

Except for autoincrement fields, all types are initialized to binary zeroes. In addition, any fields which have been assigned a default property will contain the default value.

Symbol Data Type Description
B Binary, a string 10 digits representing a .DBT block number. The number is stored as a string, right justified and padded with blanks.
C Character All OEM code page characters - padded with blanks to the width of the field.
D Date 8 bytes - date stored as a string in the format YYYYMMDD.
N Numeric Number stored as a string, right justified, and padded with blanks to the width of the field. 
L Logical 1 byte - initialized to 0x20 (space) otherwise T or F.
M Memo, a string 10 digits (bytes) representing a .DBT block number. The number is stored as a string, right justified and padded with blanks.
@ Timestamp 8 bytes - two longs, first for date, second for time.  The date is the number of days since  01/01/4713 BC. Time is hours * 3600000L + minutes * 60000L + Seconds * 1000L
I Long 4 bytes. Leftmost bit used to indicate sign, 0 negative.
+ Autoincrement Same as a Long
F Float Number stored as a string, right justified, and padded with blanks to the width of the field. 
O Double 8 bytes - no conversions, stored as a double.
G OLE 10 digits (bytes) representing a .DBT block number. The number is stored as a string, right justified and padded with blanks.

Binary, Memo, OLE Fields and .DBT Files

Binary, memo, and OLE fields store data in .DBT files consisting of blocks numbered sequentially (0, 1, 2, etc.). SET BLOCKSIZE determines the size of each block. The first block in the .DBT file, block 0, is the .DBT file header.

Each binary, memo, or OLE field of each record in the .DBF file contains the number of the block (in OEM code page values) where the field's data actually begins. If a field contains no data, the .DBF file contains blanks (0x20) rather than a number.

When data is changed in a field, the block numbers may also change and the number in the .DBF may be changed to reflect the new location.


 

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