Field value pairs (File architecture): Difference between revisions
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==BINARY or CODED fields== | ==BINARY or CODED fields== | ||
<p> | <p> | ||
The storage of <var>[[Field design (File management)#BINARY attribute|BINARY]]</var> and <var>[[Field design (File management)#CODED attribute|CODED]]</var> fields depends on whether the file has the Optimized Field Extraction (<var>FILEORG</var> X'80') bit set. Note | The storage of <var>[[Field design (File management)#BINARY attribute|BINARY]]</var> and <var>[[Field design (File management)#CODED attribute|CODED]]</var> fields depends on whether the file has the Optimized Field Extraction (<var>FILEORG</var> X'80') bit set. </p> | ||
<p class="note"><b>Note:</b> <var>FILEORG</var> X'100' files automatically also turn on x'80'. </p> | |||
<p>For files that are <i>not</i> Optimized Field Extraction Files (X'80), the field value pair contains two parts:</p> | <p>For files that are <i>not</i> Optimized Field Extraction Files (X'80), the field value pair contains two parts:</p> | ||
<ul> | <ul> | ||
<li>The field code from Table A: 2 bytes. | <li>The field code from Table A: 2 bytes. | ||
<li>The value: | <li>The value: ''always'' held as 4 bytes. | ||
</ul> | </ul> | ||
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==FLOAT fields== | ==FLOAT fields== | ||
<p> | <p> | ||
The storage of <var>[[Field design (File management)#FLOAT attribute|FLOAT]]</var> fields depends on whether the file has the Optimized Field Extraction (<var> | The storage of <var>[[Field design (File management)#FLOAT attribute|FLOAT]]</var> fields depends on whether the file has the Optimized Field Extraction (<var>FILEORG</var> x'80') bit set. </p> | ||
<p class="note"><b>Note:</b> <var>FILEORG</var> X'100' files automatically also turn on x'80'. </p> | <p class="note"><b>Note:</b> <var>FILEORG</var> X'100' files automatically also turn on x'80'. </p> | ||
<p>For files that are <i>not</i> Optimized Field Extraction files, the field value pair contains two parts:</p> | <p>For files that are <i>not</i> Optimized Field Extraction files, the field value pair contains two parts:</p> | ||
<ul> | <ul> | ||
<li>The field code from | <li>The field code from Table A: 2 bytes. | ||
<li>The value: | <li>The value: ''always'' held as 4, 8, or 16 bytes, depending on the <var>LENGTH</var> attribute. | ||
</ul> | </ul> | ||
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<li>The length of the value for this pair (1 to 4): 1 byte. | <li>The length of the value for this pair (1 to 4): 1 byte. | ||
<li>The value: | <li>The value: ''always'' held as 4, 8, or 16 bytes, depending on the <var>LENGTH</var> attribute. | ||
</ul> | </ul> | ||
<p> | <p> | ||
By storing a length with < | By storing a length with <i>all</i> field occurrences, data in records can be read much faster. The possible trade-off on performance versus space is discussed in [[File design (File management)#X'80' - Optimized Field Extraction files|X'80' - Optimized Field Extraction files]].</p> | ||
[[Category:File architecture]] | [[Category:File architecture]] | ||
Revision as of 00:32, 23 January 2014
Overview
The basic unit of storage inside a Model 204 record is the field value pair (or, more literally, "field = value pair"). A record or a field group contains a series of field groups and field value pairs.
A record can contain multiple field value pairs for fields with the OCCURS attribute.
A record or a field group can contain non-OCCURS field value pairs, whose physical structure is described below, for each storage data type.
STRING fields
The field value pair for STRING fields contains three parts:
- The field code from Table A: 3 bytes for FILEORG X'100' files, or 2 bytes for all others.
- The length of the value for this pair (0 to 255): 1 byte.
- The value: variable length, 0-255 bytes.
For example, a NAME field containing 'SMITH' is held in either 8 or 9 bytes (depending on the FILEORG), while a NAME of 'FRANKENSTEIN' is held in either 15 or 16 bytes.
BINARY or CODED fields
The storage of BINARY and CODED fields depends on whether the file has the Optimized Field Extraction (FILEORG X'80') bit set.
Note: FILEORG X'100' files automatically also turn on x'80'.
For files that are not Optimized Field Extraction Files (X'80), the field value pair contains two parts:
- The field code from Table A: 2 bytes.
- The value: always held as 4 bytes.
For Optimized Field Extraction Files, the field value pair contains three parts:
- The field code from Table A: 3 bytes for FILEORG X'100' files, or 2 bytes for all others.
- The length of the value for this pair (1 to 4): 1 byte.
- The value: variable length, 1-4 bytes.
By storing a length with all field occurrences, data in records can be read much faster. The possible trade-off on performance versus space is discussed in X'80' - Optimized Field Extraction files.
FLOAT fields
The storage of FLOAT fields depends on whether the file has the Optimized Field Extraction (FILEORG x'80') bit set.
Note: FILEORG X'100' files automatically also turn on x'80'.
For files that are not Optimized Field Extraction files, the field value pair contains two parts:
- The field code from Table A: 2 bytes.
- The value: always held as 4, 8, or 16 bytes, depending on the LENGTH attribute.
For Optimized Field Extraction files, the field value pair contains three parts:
- The field code from Table A: 3 bytes for FILEORG X'100' files, or 2 bytes for all others.
- The length of the value for this pair (1 to 4): 1 byte.
- The value: always held as 4, 8, or 16 bytes, depending on the LENGTH attribute.
By storing a length with all field occurrences, data in records can be read much faster. The possible trade-off on performance versus space is discussed in X'80' - Optimized Field Extraction files.