Topics for Database Administrators

Changing a Database Definition

Changes to a database definition can affect view descriptor files. The interface view engine validates the view against the current definition and issues an error message if it detects discrepancies.

The following sections contain details about the effects of changes to a SYSTEM 2000 database definition on existing view descriptors.

Changes that do not affect existing view descriptors:
- creating or deleting indexes
- inserting new schema items
- deleting schema items not referenced in any view descriptor
  
  Note: If an access descriptor includes the deleted schema item, users might create a view descriptor using that item, which would cause a problem.
- inserting or deleting schema records in paths not referenced in any view descriptor
  
  Note: If an access descriptor references the changed path, users might create a view descriptor using that path, which would cause a problem.

Changes that might affect existing view descriptors:
- changing an item name. If the item name was used in a where-clause or an ordering-clause that is stored in the view descriptor, a syntax error message appears when you try to use the view descriptor. The message indicates an unrecognized component name.
- changing the attributes of items that are not in the view descriptor but are referenced in the stored where-clause.

Changes that cause existing view descriptors to fail:
- inserting or deleting a level in the path of a view descriptor.
- changing the attributes of an item or the component number of an item, so that it points to something different. Specifically,
  - you can change the pictures for CHARACTER, TEXT, and UNDEFINED item types, but you cannot change them to a DATE or NUMERIC item type.
  - you cannot change a DATE item type to any other item type.
  - you cannot change a NUMERIC item type to a non-numeric item type or change its picture.
- changing the component number of parent records for any schema item or record in the path of a view descriptor.
- deleting items that are referenced in a view descriptor.

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