Oracle Objects for OLE in Oracle9i
Oracle Objects for OLE (OO4O) is a COM-based database connectivity tool that combines seamless and optimized access to Oracle databases with easy to use interfaces. OO4O can be used in a variety of environments ranging from web applications to n-tier client/server applications. It can be used from virtually any programming or scripting language that supports the Microsoft COM Automation technology, such as Visual Basic, Active Server Pages, Visual C++, VBA in Excel, PowerBuilder, Delphi, Microsoft Internet Information Server, and COM+/Microsoft Transaction Server.
Because it is an Oracle native driver, OO4O provides fast performance on Windows clients to Oracle databases. It does not incur the overhead of ODBC and OLE DB drivers. OO4O has been developed and has evolved specifically for use with Oracle database servers. It provides easy access to features that are unique to Oracle, but are otherwise cumbersome or inaccessible to use from ODBC and OLE DB-based components, such as ADO.
OO4O consists of an in-process COM Automation Server, a C++ class library, and the Oracle Data Control.
OO4O include the following major features:
Below are descriptions of some of the major features:
OO4O provides full support for accessing and manipulating instances of REFs, value instance, Variable-length arrays (VARRAYs), Nested tables, and LOBs.
Instances of these types can be fetched from the database or passed as input or output variables to SQL statements and PL/SQL blocks, including stored procedures and functions. All instances are mapped to COM Automation Interfaces that provide methods for dynamic attribute access and manipulation.
COM+/MTS is essentially a COM-based TP-Monitor and relies on the Microsoft Distributed Transaction Coordinator (DTC) for distributed transaction support. Oracle database transactions initiated in OO4O automatically participate in global transactions coordinated by the MS DTC in MTS, provided that Oracle Services for MTS is installed and running. Database connections established in components deployed in MTS can also be pooled via the Oracle Services for MTS.
OO4O will use this API to provide the capability for enlisting user sessions contained in the OraDatabase Automation interface with DTC. All transactions on these user sessions are controlled by DTC after enlistment is completed. After an OraDatabase is enlisted with DTC, all local transactional operations for that object are disallowed.
OO4O provides interfaces for accessing the Advanced Queuing (AQ) feature in the Oracle database. It makes AQ accessible from popular COM-based development environments, such as Visual Basic.
The OraAQ Automation interface provides methods for enqueuing and dequeuing messages (OraAQMsg). It also provides a method for monitoring queues for message arrivals. Client applications are notified when messages of interest are dequeued via a callback object.
OO4O allows multiple user sessions to share a network connection to an Oracle Server. This capability is particularly useful for application components that use OO4O in n-tier distributed environments, such as a web environment.
OO4O includes interfaces for retrieving attributes of schema objects. Using the Describe method of the OraDatabase interface retrieves attributes. This method takes the name of a schema object (e.g. emp) and returns a COM Automation object (OraMetaData). OraMetaData provides methods for dynamically navigating and accessing all the attributes (OraMDAttribute collection) of a schema object described.
XML is quickly becoming one of the common data formats for Internet applications. In Oracle9i, OO4O introduces XML support, allowing users to easily extract and insert data from the Oracle database in XML format. OO4O users can now flexibly render XML from a dynaset object. The XML support includes the ability to use advanced data types and to control the XML output format.
OO4O and the Oracle9i database add this globalization support with full UCS2 Unicode support. Using Unicode in OO4O is transparent, requiring no application code changes. This makes developing global applications with OO4O easy and fast.
This feature supports asynchronous notification of database events to interested subscribers. Under this model, the client can subscribe to one or more database events. Each database event that the client is interested in is stored as a subscription. When a database event of interest is triggered, the client subscriber's database event handler for that event is fired and the subscriber is notified. The database event subscriber is required to create a subscription, based on the database event of interest. At the time of subscription creation, the subscriber should provide an event handler. The database event handler should be an automation object that implements the NotifyDBEvents method. OO4O invokes the NotifyDBEvents method of the event handler when the particular database event is fired.
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