What is OLE DB?

OLE DB API

OLE DB is a standard application programming interface (API) developed by Microsoft. It is a component of Microsoft’s Data Access Components software. OLE DB allows an application to access a variety of data for which OLE DB data providers exist. It provides an application with uniform access to data stored in diverse formats, such as indexed-sequential files like Btrieve, personal databases like Paradox, productivity tools such as spreadsheets and electronic mail, and SQL-based DBMSs.

The OLE DB interface supports direct connections to SQL-based databases.

Accessing data through OLE DB

Applications like InfoMaker that provide an OLE DB interface can access data for which an OLE DB data provider exists. An OLE DB data provider is a dynamic link library (DLL) that implements OLE DB function calls to access a particular data source.

The InfoMaker OLE DB interface can connect to any OLE DB data provider that supports the OLE DB object interfaces listed in Table 4-1. An OLE DB data provider must support these interfaces in order to adhere to the Microsoft OLE DB 2.0 specification.

**Table 4-1: Required OLE DB interfaces**
IAccessor	IDBInitialize
IColumnsInfo	IDBProperties
ICommand	IOpenRowset
ICommandProperties	IRowset
ICommandText	IRowsetInfo
IDBCreateCommand	IDBSchemaRowset
IDBCreateSession	ISourcesRowset

In addition to the required OLE DB interfaces, InfoMaker also uses the OLE DB interfaces listed in Table 4-2 to provide further functionality.

**Table 4-2: Additional OLE DB interfaces**
OLE DB interface	Use in InfoMaker
ICommandPrepare	Preparing commands and retrieving column information.
IDBInfo	Querying the data provider for its properties. If this interface is not supported, database connections might fail.
IDBCommandWithParameters	Querying the data provider for parameters.
IErrorInfo	Providing error information.
IErrorRecords	Providing error information.
IIndexDefinition	Creating indexes for the extended attribute system tables. Also creating indexes in the Database painter. If this interface is not supported, InfoMaker looks for index definition syntax in the pbodb125.ini file.
IMultipleResults	Providing information.
IRowsetChange	Populating the extended attribute system tables when they are created. Also, for updating blobs.
IRowsetUpdate	Creating the extended attribute system tables.
ISQLErrorInfo	Providing error information.
ISupportErrorInfo	Providing error information.
ITableDefinition	Creating the extended attribute system tables and also for creating tables in the Database painter. If this interface is not supported, the following behavior results: InfoMaker looks for table definition syntax in the pbodb125.ini file InfoMaker catalog tables cannot be used DDL and DML operations, like modifying columns or editing data in the database painter, do not function properly
ITransactionLocal	Supporting transactions. If this interface is not supported, InfoMaker defaults to AutoCommit mode.

Accessing Unicode data

Using the OLE DB interface, InfoMaker can connect, save, and retrieve data in both ANSI/DBCS and Unicode databases but does not convert data between Unicode and ANSI/DBCS. When character data or command text is sent to the database, InfoMaker sends a Unicode string. The data provider must guarantee that the data is saved as Unicode data correctly. When InfoMaker retrieves character data, it assumes the data is Unicode.

A Unicode database is a database whose character set is set to a Unicode format, such as UTF-8, UTF-16, UCS-2, or UCS-4. All data must be in Unicode format, and any data saved to the database must be converted to Unicode data implicitly or explicitly.

A database that uses ANSI (or DBCS) as its character set might use special datatypes to store Unicode data. Columns with these datatypes can store only Unicode data. Any data saved into such a column must be converted to Unicode explicitly. This conversion must be handled by the database server or client.