Table A (File architecture)

Table A contains three structures:

A dictionary of the fieldgroup / field names and their attributes.

Some attributes (notably 'CODED') require lists of values to be maintained. These lists are stored either in the FEW-VALUED or MANY-VALUED structures.

Table A usually is small in relation to the rest of the file.

Internal File Dictionary

Defined by the ATRPG.

The internal file dictionary is a hashed file where each page contains up to ASTRPPG field or field group definitions.

Each entry contains the field code (the representation of the field as physically used in records); the field name; and the attributes as assigned by the DEFINE FIELD command (or by a redefinition).

Non FILEORG x'100' Files

The maximum number of fields (the sum of ASTRPPG * ) in any Model 204 file is 4000.

Even when the product of the above is 4000, this number may not actually be reached because of wasted entries (where ASTRPPG is defined too large) or due to vagaries of the hashing algorithm.

FILEORG x'100' Files

With the introduction of X'100'files (in Model 204 V7R5) the maximum number of fields (ASTRPPG * ATRPG) has been increased to 32000. In order to support this increase, as well as the additional attributes. the field code has been increased from 2 to three bytes.

Where the maximum number of fields exceeds 4000, no fields may be defined as KEY or NUMERIC RANGE.

Many and Few Valued Pages

If a field has the CODED or FRV attribute, a complete list of the values that the field has ever had (since it was last created or reorganized) is held in either FEW-VALUED or MANY-VALUED pages in Table A (with the latter the default).

Both of these sets of pages should be kept very small.