X/Open's DTP Model

The X/Open Distributed Transaction Processing (DTP) model is shown in the diagram below:

The point of the X/Open DTP model is to define the interfaces between these components, so that different products from different vendors can interoperate.

Six interfaces are shown in the above diagram. Five of them are defined by the DTP model. The communication between the application and the resource manager is not defined. DTP assumes that standard database languages, such as ISAM (Indexed Sequential Access Method) or SQL (Structured Query Language), will be used here.

• The most well known part of this standard is the interface between the resource managers and the transaction manager, known as XA. Most resource managers, such as RDB (relational database) systems, are "XA compliant". This means that they can participate in transactions, including being a participant in two-phase commit. Transaction managers use

  xa_start

  ,

  xa_commit

  and

  xa_rollback

  calls to manage a transaction. Resource managers use

  xa_reg

  calls to register with the transaction manager. XA also allows one-phase commit for transactions that access a single resource manager.
  
  
• The XA+ standard is a superset of the XA standard. The extension is used by the communication resource manager to tell the transaction manager that a node (i.e. another transaction manager) has joined the transaction.
  
  
• The TX standard is used to communicate between application programs and the transaction manager. Applications issue

  tx_begin

  ,

  tx_commit

  , and

  tx_rollback

  calls to manage transactions.

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