You can define the 8-byte constant field with the protect and dark attributes. The attribute byte on the form becomes the attribute byte in the EGL-generated MFS map. The 8-byte constant contains the name of the IMS transaction that is started when the form is processed. Specifying the constant on the form enables the user to specify the IMS /FORMAT command to display a formatted screen to start a transaction. Do not use the /FORMAT command if variable fields on the form have initial default values. If the /FORMAT command is used, the default values do not appear.
If you do not define an 8-byte, protected, dark constant on the form, EGL searches for any string of 9 blanks on the form and sets this area aside as a protected, dark variable field (1 byte attribute, 8 bytes of data) in the generated MFS map. The generated program uses this field to store the name for the next IMS transaction to be run after a converse statement, or after a transfer statement of the form transfer to a transaction that includes a map. The user cannot use the /FORMAT command to start a transaction for these maps because IMS does not have a default transaction name.
You do not need to explicitly define the 2-byte area on a form. EGL selects two adjacent blank bytes on the map and treats it as a protected, dark variable field (1 byte attribute, 1 byte of data).
For 3270-type devices, a single set of statements describes both the DIF and the DOF. For printers, only a DOF is needed. Each device field is given a name that statements can refer to in the message input and output descriptors.
For EGL FormGroup parts, the DOF is always larger than the DIF because the DOF includes form constants.
The following formula helps you estimate the size of the DOF:
DOF Size = 150 + 388 * Number of printer forms in the formGroup + 208 * Number of display forms in the formGroup + 63 * Number of variable field occurrences on display forms in the formGroup + 62 * Number of constant fields on display forms in the formGroup +1.12 * Total length of all constant fields on display forms in the formGroup
DOF Size = 206 + 68 * Number of printer forms in the formGroup + 374 * Number of display forms in the formGroup + 63 * Number of variable field occurrences on printer forms in the formGroup + 62 * Number of constant fields on printer forms in the formGroup +1.12 * Total length of all constant fields on printer forms in the formGroup
MOD Size = 36 + 724 * Number of display forms in the formGroup + 202 * Number of printer forms in the formGroup + 52 * Number of variable field occurrences in the formGroup
MID Size = 36 + 858 * Number of display forms in the formGroup + 52 * Number of variable field occurrences for display forms in the formGroup
Related concepts
IMS runtime support