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Introduction to Microsoft DNA
The Data Access Layer  
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Several Microsoft products address the needs of the Data Access layer.

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.

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.

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.

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.

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.

Data Access with ADO and OLEDB  
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.

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.

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.

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.

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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