bdfd1m0l | Database Administration |
Each LREC in the aircraft file contains the fields shown in Table 28. Table 28 also shows the number of bytes in each
field.
Table 28. LREC Fields for the Aircraft File
Field | No. of bytes |
---|---|
size | 2 |
key | 1 |
aircraft type | 4 |
seat range | 8 |
seat class | 1 |
Total | 16 |
Each LREC in the aircraft file therefore contains 16 bytes.
Because the database must be able to accommodate 50 aircraft types and three classes, you can calculate the required amounts of data as follows:
no. of aircraft types x no. of classes x LREC size = amount of data
The calculation is:
50 x 3 x 16 = 2400 bytes
This comparatively small number of bytes fits comfortably into a fixed block of size L4 (4095 bytes, including header and trailer). Because only one block is required, you can use a miscellaneous file.
The aircraft file contains only one block of data. Because of this, all the data can be held in a single subfile, and you do not need to distribute the aircraft LRECs over many subfiles. Because you are using a single subfile, use the single-subfile algorithm (#TPFDB04) to distribute the LRECs in the file.
Although the aircraft file is small at the moment, it may well need to expand in the future. Therefore, consider now how a data overflow might be accommodated.
Because the aircraft LRECs are only 16 bytes long, there is already some room for expansion in the existing L4 (4095 bytes) block. Overflow blocks of L2 size (1055 bytes) should be adequate for future needs.
When deciding the structure of the LRECs, consider how the TPFDF product
will interrogate the file.
The aircraft file is not an index file, so the LRECs do not need to contain
pointers. The TPFDF product needs only the aircraft type, so the
aircraft LREC structure can be as follows: