Client/Server Architecture and Data Access - Microsoft SQL Server 2008 Analysis Services - page 572

Query Management for Applications Written in Native Code
As with earlier versions of Analysis Services, you can access data by using the interfaces of
OLE DB. OLE DB is a collection of standard interfaces, based on COM, that make it possi-
ble for client applications to access data from various data sources. OLE DB for OLAP was
released in 1997, and is based on OLE DB, but is designed specifically for access to multi-
dimensional data. OLE DB for Data Mining (OLE DB DM), an extension to the existing
standard, was released in 2000. Analysis Services supports all three, collectively known as
Analysis Services OLE DB provider.
The OLE DB provider is the optimal way of connecting to Analysis Services from client
applications written in native code. A disadvantage of OLE DB, other than that it is pretty
complex, is that you can't use OLE DB interfaces in certain applications, such as those
written in Visual Basic and scripting languages, such as VBScript, JScript, and other
languages that use automation.
Visual Basic works only with classes that implement the IDispatch interface; OLE DB
classes implement the IUnknown interface. If you want to write your application in Visual
Basic or another language that supports automation, you need another layer above the
OLE DB provider: ADO or ADOMD. These layers accept calls from client applications and
delegate them to OLE DB or Analysis Services OLE DB, which in turn communicates
directly with the data source.
This way of accessing data stored in Analysis Services is not new, but it makes it possible
for the majority of applications existing today to work. Figure 31.5 shows how ADO and
ADOMD work with the providers.
Query Management for Applications Written in Managed Code
In developing the .NET Framework technology, Microsoft updated its approach to data
access technology with ADO.NET, not only adding the capability to work with managed
code, but also reviewing the architecture and principles of data access. ADO is a layer
above OLE DB providers, delegating all calls to OLE DB. With ADO.NET, Microsoft intro-
duced the concept of the ADO.NET provider—a managed assembly that implements the
standard interfaces defined by ADO.NET, allowing you to work with data stored in a
specific database.
Microsoft has released three ADO.NET providers with the .NET Framework: SqlClient ,
OracleClient , and OledbClient . The first two providers enable your application to work
with data stored in SQL Server and Oracle databases, respectively. The third provider is a
logical continuation of ADO and enables your application to work with existing OLE DB
providers.
ADO.NET providers are written for working with a specific data source, and are the most
efficient means for working with that database. If there is a specific provider for the data
source you're working with, we recommend that you use it instead of the more universal
OledbClient .
If you are writing your application in managed code, we advise you to use ADOMD.NET
to access data stored on Analysis Server. ADOMD.NET is not a layer above the OLE DB