The Data Access Layer
June 5, 2000
Several Microsoft products address the needs of the
Data Access layer.
From within the defined product range Microsoft
supplies 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, develops 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 returned 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 systems 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.
Next month we'll take a look at the ASP Environment.
Additional Resources:
The Business Layer Technology.
Introduction to ASP For Web Developers | Table of Contents
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