Record (File architecture)

Overview

A Model 204 Record is a collection of fields (either individually or in Repeating Field Groups (RFGs)) containing a set of data about a thing. Admittedly, this is a very vague description, because the flexibility of Model 204 permits the File Manager to create files whose records are best suited to the required purpose, whatever it may be.

Each record is variable in length and need contain only the fields that pertain to it. The limit of the number of field value pairs in a record is in the tens of millions.

There is only a limited fixed format for data within a record (pre-allocated fields). Almost any number of fields can appear almost any number of times in almost any order. Each record is automatically assigned a unique internal record number that is used by the system to build index entries for the record.

For example, the following code:

IN filename STORE RECORD END STORE

Does, in fact, physically store a record. It has been assigned an #Internal Record Number and would contain the pre-allocated field structure (if any), but no data.

The Concept of a Model 204 Record

As noted above, a Model 204 record is highly variable in length.

The Internal Record Number (IRN)

not permanent (changes during a reorganization)

used as target index (both hashed and B-tree indexing)

The Structure of a Model 204 Record

Data

If there are any preallocated fields in a file (see the OCCURS attribute) every record in that file will begin with the set of such fields. The set of fields is stored in the Record Map in Table D.

After the preallocated fields, is the rest of the data; a series of: field value pairs; repeating field groups; and / or pointers to large objects. These will be physically positioned in either the order they were ADDed (which always adds the entity at the end of the record), or positioned by an INSERT statement.

Each of the four is described below: