# Processing codes overview

Processing codes describe database links and data manipulation
rules in dictionaries. The D3 dictionary defines file layouts and
data structures.

Processing codes are used by various D3 system processors,
such as the Update processor, to transform the value of data. Processing
codes are stored in attribute-defining and file-defining items in
file dictionaries. The processing codes are found in:

| Attribute 4 | Structure |
| --- | --- |
| Attribute 7 | Output-Conversion |
| Attribute 8 | Correlative |
| Attribute 14 | Input-Conversion |
| Attribute 20-30 | Hotkey (see Update processor) |
Output-conversion codes manipulate the display or format
of data. They are applied prior to output from the Update processor,
the Access List processor, or a FlashBASIC call.

Correlative
codes are used by all the system processors. Correlative codes for
attributes are applied by the sort or select processor when building
a list of item-IDs and by the Update processor and the List processor
prior to calling the output-conversions. Correlative codes in file-defining
items are called when the item is filed, especially from the Update
processor. Some correlative codes, such as stamps, item-ID generation,
and FlashBASIC subroutines, are only called from the Update processor.

More than one processing code can be specified in an attribute
by separating the codes with value marks (CTRL+V in the Update processor).

Input-conversion codes are used by the Update processor to validate
data as it is entered. These codes include:

- Algebraic functions

- Edit patterns

- D3 assembly code executions

- FlashBASIC calls

- Range limitations

- Required fields

Input-conversion codes define single or multiple file indexing.
This allows cruising through both the current file (that is, the file
where the item resides) and other linked files.

## See also

- [Internal format](https://d3codex.com/definitions/internal-format/)
- [seq](https://d3codex.com/definitions/seq/)

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Source: https://d3codex.com/processingcodes/processing-codes-overview/ - part of the D3Codex reference.