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LAST UPDATED: December 28, 2004
Using Microsoft COM+/DTC with UniAccess
UniAccess support for distributed transactions is based upon Microsoft’s COM+ architecture. The COM+ programming model provides a framework for developing components that encapsulate business logic. The COM+ run-time environment is a middle-tier platform for running such components. One of the biggest advantages in using COM+ is support for automatic transactions. COM+ run-time can automatically initiate transactions to satisfy the component’s transaction expectations. COM+ components can be declared so that their objects always execute within a transaction, regardless of how the objects are created. In turn, when a transactional component opens a database connection, COM+ automatically enlists the database connection in the component’s current transaction. Hence, the updates made over various database connections opened by the COM+ component become part of a single transaction.
COM+ relies on Microsoft’s Distributed Transaction Coordinator (MS DTC) to act as the transaction manager responsible for coordinating transactions across participating databases. MSDTC uses the OLE Transaction (OLE Tx) protocol for transaction management. It also supports Transaction Internet Protocol (TIP) for databases that do not support OLE Tx. TIP is an Internet RFC that describes a standard two-phase commit protocol. It enables heterogeneous transaction managers to coordinate distributed transactions. UniAccess uses the TIP protocol to communicate with MS DTC.
The following diagram demonstrates how UniAccess fits into the COM+ architecture. Business logic is encapsulated as COM+ components or transactional Active Server Pages (ASP). When these components or pages are invoked, COM+ automatically initiates an MS DTC-managed transaction. When these same components utilize UniAccess to access OS 2200-based distributed transaction-enabled resources, the UniAccess Distributed Transaction Coordinator
1 Microsoft SQL Server, IBM DB2, Oracle, Sybase Adaptive Server, and Informix currently have products that support COM+/DTC integration.
2 UniAccess has always provided support for local transactions. For example, you can use ODBC to start a transaction, make changes, and then commit or rollback changes. However, unlike distributed transactions, the unit of work is limited to only one database per transaction.
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(UADTC) is responsible for communicating with MS DTC via the TIP protocol and with the UniAccess OS 2200-based components to coordinate distributed transaction processing. In turn, the UniAccess OS 2200-based components rely on standard OS 2200 system facilities such as Step Control and Integrated Recovery Utility (IRU) to perform two-phased commits in response to UADTC messages.
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