IMS transaction types

Transactions are the most common data type sent from a workstation to IMS. IMS supports two kinds of transactions—update and inquiry.

An update transaction can modify a database. An inquiry transaction can look at data in a database but cannot change or update it. Transactions are defined as update or inquiry during IMS system definition.

An additional attribute is defined for inquiry transactions—recoverable or irrecoverable. Recoverable-inquiry transactions are always recoverable no matter which element in the network fails. Irrecoverable-inquiry transactions are not recovered following an I/O error condition or IMS system restart.

All update transactions are recoverable.

All Fast Path transactions must be defined as recoverable, but can be either inquiry or update.

A workstation can be defined to handle one or both types of transactions. Other decisions and processing might be required of the controller or controller application program when both recoverable and irrecoverable transactions are handled. The decision to define a transaction as recoverable or irrecoverable requires an evaluation of the advantages and disadvantages that each transaction type offers to the individual operating environment.

The following topics describe the inquiry message types and the responses required for each.