data_layer.html

this gives an introduction to microsoft dna.

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The Data Access Layer
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<P>

Several Microsoft products address the needs of the
Data Access layer.

<P>

From within the defined product range Microsoft 
supplys a production level enterprise database 
solution, MS SQL Server. SQL Server provides 
facilities for running databases for any kind of 
traditional solution including On-Line Transaction 
Processing (OLTP) and Analytical Processing.(OLAP). 
SQL Server is tightly integrated into the NT architecture 
and provides facilities for automatic maintenance and 
performance optimization.

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Databases are not the only data stores however and 
Microsoft produces a feature rich, Internet connectable, 
Mail Server solution. Exchange Server is aimed at 
Collaborative and Information Sharing. Within the DNA 
application structure, Exchange also acts as a repository, 
a business rule engine, and a content delivery mechanism.

<P>

To access information about other services, developes and 
resources within the application infrastructure 
can use ADS, the Active Directory Service. ADS provides 
access to a hierarchical tree of information spanning 
the network resources and beyond. A distributed store 
of this information maintains and serves data to 
applications that query it. The information may be 
users, groups, machine information, services and even 
other databases.

<P>

NTFS provides the file system of choice within the DNA 
application and can be considered as another data source. 
The facilities provided by the NT File System are extensive 
and well document. To find out more, you may go to 
http://www.microsoft.com/ntserver.

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One other data repository deserves note. The Microsoft 
Index Server is a product to enable the indexing of web, 
word processing, and other office based documents. By 
default, Index server provides an API and example ASP 
pages to enable web-based access for researching content. 
Often Index Server is used to enable searching a portal. 
Several sources of information are indexed. When a client 
requests a search, it is performed and the results are 
interpreted and return to the user in order for them to 
take further action.

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Data Access with ADO and OLEDB
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The data access layer can only be useful if the tools used 
to access those repositories are consistent and simple. To 
address this issue Microsoft created several levels of 
technology. 

<P>

In the simplest form, DNA needed to provide Business layer 
components with the facility to gain different levels of 
access to data. These layers provide simple abstract methods 
to access the data source tight through to technologies to 
implement drivers to custom data sources.

<P>

The primary data source access is provided via ActiveX Data 
Objects (an agreed variant of a COM object, one that supports 
particular implementation details. ADO abstracts the details 
of the implementation of data access and constructs a consistent 
data model. Using COM as the delivery mechanism for drivers and 
consumers means that an agreed supporting infrastructure can be 
implemented. 

<P>

For example, because ADO abstract data source details 
away from the consuming developer it is possible to 
write data access routines that work for several differing 
data systems without change. Those data system can be very 
different. ADO uses the facilities of OLE DB to provide the 
unified data access. In fact, ADO is the higher-level data 
access from Universal Data Access technology group. Within 
the UDA there are a number of data access technologies, 
however, ADO and OLE DB are the primary focus in DNA 
applications.

<P>

OLE DB is the underlying technology that ADO and other Data 
Source technologies use. OLE DB is a specification and 
implementation for building drivers for both aspects of 
the data access problem. Providers are the implementation 
of a driver to enable Consumers to access the data. OLE DB 
enables providers to work against a code base and conceptual 
framework in order to enable conformance to a data object 
model that all consumers can access. When all data source 
providers implement their access in the same manner, through 
similar standardized interfaces consumers will be able to use 
a "code template" to access any provider.

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