HP Intelligent Management Center Standard Software Platform - Manual (Page 718)

In addition, data access is simple. Direct access database files are
point-and-click data sources. You need only select the required database
files, and Crystal Reports will read all the stored data.
Disadvantages
When you access a database directly through Crystal Reports, only that
database type can be used by the report. You cannot switch to a different
type of database or table without creating a new report.
For example, if you design a report based on Pervasive data, you cannot
change the tables accessed by the report to Access data. Crystal Reports
communicates with Pervasive data using Pervasive-specific syntax, a syntax
that is not compatible with Access data.
If you access data through ODBC, on the other hand, the syntax used is
always the SQL language, regardless of the actual database type. See
ODBC
data sources .
Three layers
Direct access of database files from Crystal Reports requires three layers:
• Crystal Reports
• Data translation
• Database
Crystal Reports uses the data translation layer to talk to the database and
access its data.
Crystal Reports
Crystal Reports operates as an interface through which you can format,
arrange, select, and sort the data stored in database files. It obtains data by
communicating with one or more files in the data translation layer that can
actually read the database. Since Crystal Reports can work with many forms
of data, it must rely on other files in order to work directly with the data.
718 Crystal Reports 2008 SP3 User's Guide
Accessing Data Sources 26
Direct access database files