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FSCAN can operate on databases having the following attributes:

• The databases are FOCUS databases, not databases of other types.
• The databases are individual databases, not combined structures created by the COMBINE command.
• The length of the root key field in the database does not exceed 61 bytes, and the sum of the field name length plus the field length does not exceed 73 bytes.

Also, note the following regarding databases:

• FSCAN does not accept alternate file views.
• Databases that you specify with the USE command using the READ option are write protected.
• Databases that you are viewing on a FOCUS Database Server in Simultaneous Usage mode are write protected.

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The following rules apply to the display and editing of segments in FSCAN:

• FSCAN does not display a segment containing a key field longer than 61 bytes and the sum of the field name length plus the field length does not exceed 73 bytes, nor does it display the descendants of that segment.
• When you input a new segment instance, the instance must have a key unique to its group. (In the root segment, this means all the instances in the segment; in a descendant segment, this means all the instances that share a parent instance). If you try to input an instance with a duplicate key, FSCAN will generate an error message.
• If you change a key field value of an instance, the new instance key (the combination of all key field values in the instance) must be unique to the group. If you try to change the key to a duplicate, FSCAN will generate an error message.
• If you use FSCAN on segments already containing duplicate keys, the results are unpredictable. If the root segment has duplicate keys, an attempt to display a screen with these duplicates results in FSCAN terminating in an error. If a descendant segment has duplicate keys, an FSCAN error is displayed and you are positioned at the parent segment.
• When a segment is type S0 or blank, no one field is designated as the key field. FSCAN considers all fields in such segments to be key fields. This has two ramifications:
  • You cannot input a segment instance that is the duplicate of another in the same group.
  • You cannot update a segment instance so that it duplicates another segment instance in the same group.

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FSCAN can display fields containing the following attributes:

• The field length does not exceed 61 bytes and the sum of the field name length plus the field length does not exceed 73 bytes.
• The fields are real database fields, not DEFINEd fields.
• FSCAN displays group fields as their individual members, not as a group.

Note: Text fields cannot be displayed in FSCAN.

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How FSCAN treats the changes you make to the database depends on whether the database is protected by shadow paging.

If you are using shadow paging, FSCAN writes your changes to a shadow database. If you enter the commands END, FILE, or SAVE, the changes become part of the real database. If you enter the command QQUIT or if FSCAN terminates abnormally, the changes disappear and the database is not affected.

If you are not using shadow paging, FSCAN writes your changes directly to the database. The changes remain even after you enter the QQUIT command.

FOCUS performs shadow paging using the Absolute File Integrity facility.

Note: Absolute File Integrity and shadow paging are not supported for XFOCUS data sources.

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If the database is protected by the DBA security facility, then the ACCESS attribute in the Master File restricts users in the following way:

• Users with read-write access (ACCESS=RW) and write-only access (ACCESS=W) have unrestricted access to the database, with the exception of what is denied them by the RESTRICT and NAME attributes.
• Users with update-only access (ACCESS=U) can display the entire database, with the exception of what is denied them by the RESTRICT and NAME attributes. However, they cannot input or delete instances and can only update non-key fields.
• Users with read-only access (ACCESS=R) to any part of the database cannot use FSCAN on the database.

FSCAN honors DBA security restrictions on segments and fields. FSCAN does not display those segments and fields from which the user is restricted. FSCAN does not honor DBA field value restrictions and will display all field values regardless of the user.

If the user has no access to a key field in the root segment, that user is blocked from using FSCAN on the database.

If the user has no access to a segment, that segment is not listed on the menu that appears when the user enters the CHILD command.