HP Intelligent Management Center Standard Software Platform - Manual (Page 732)

Finally, by using SQL pass-through technology to send an SQL statement
to ODBC and retrieve an initial set of data, Crystal Reports off-loads much
of the data retrieval and sorting work on to the server system, freeing up
local memory and resources for more important tasks. In addition, only the
data specified by the SQL statement is returned to Crystal Reports, reducing
network traffic and the use of network resources. By working more efficiently
with the original data, Crystal Reports saves you time and effort, and lets
you concentrate on the design process and other more important work.
Disadvantages
There are many layers involved in passing data through ODBC from a
database to an application. First, Crystal Reports must request some data.
The request must be translated by the ODBC translation layer into a format
that ODBC understands (an SQL statement). ODBC must determine where
the requested data exists, and pass the request on to the ODBC data source.
For more information, see
DBMS translation (ODBC data source) layer . The
data source must analyze the request and translate it again into a format
that can be understood by the DBMS. This complex process can fail at any
of several possible levels.
In addition, ODBC data sources must be correctly configured and set up in
the Odbc.ini and Odbcinst.ini files before they can be used. If you create a
report on one system and try to open it on another system that does not have
the same ODBC data source set up, Crystal Reports will not be able to
connect to the data.
When working with ODBC, you should also be aware that the SQL language
used by ODBC is based on the standards set for the SQL language by the
American National Standards Institute (ANSI). Some SQL-based DBMS
applications, however, provide additional features to the SQL language that
are specific to that DBMS. If your data uses features unique to your DBMS,
ODBC will not be able to translate those features (though in many cases it
will still retrieve most of the data). See
The SQL language .
Five layers
The process by which Crystal Reports accesses data from an ODBC data
source consists of five layers:
732 Crystal Reports 2008 SP3 User's Guide
Accessing Data Sources 26
ODBC data sources