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Page Title:
Table 38. Format for variable-length index (*.*X) files. |
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|  MIL-D-89009
TABLE 38.
Format for variable-length index (*.*X) files.
Starting
No.
Position
of
Field
(Bytes)
Bytes
Type
Description
0
4
Integer
Number of records (N) in table being
indexed
4
4
Integer
Number of bytes in header of table being
indexed
8
16
Integer
A two-dimensional array of 4 byte
Array
integers defined as:
[n][0]=Byte offset from beginning of file
[n][1]=Number of bytes in table record
where n ranges from 1 to N
c. Variable-length index file. The variable-length index
is a separate file that is mandatory when a VPF table
contains variable-length records. TABLE 38 describes
the format for the variable-length index files. The
file has two parts: a header and a data array. Each
entry in the data array relates to a record in the VPF
table.
The data array identifies the location of every record
in the variable-length file by containing the following
entries for each record:
[n][0]
=
Byte offset from beginning of file
[n][1]
=
Number of bytes in table record
where n is an integer from 1 to N. The term byte offset
refers to a location with respect to the beginning of a
file. The first byte of a file has an offset of zero.
Thus, if the software requires the location of record 45
in a VPF table, the index file can be used to locate the
exact position of the record without sequentially
searching for the match. The entry for record 45 in the
variable-length index would indicate the byte offset in
the VPF table to the position of record 45 and the
number of bytes in record 45.
d. Value description tables. Value description tables
specify the attribute codes for features in a coverage,
organized by feature class, and provide a description
for each attribute value. Appendix Section 30.3 (data
dictionary) specifies the format and content for all of
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