OpenEdge Data Management: DataServer for Microsoft SQL Server

Introduction
1–6
As shown in Figure 1–2, when you execute an application that accesses a MS SQL Server
database, the compiler translates ABL or SpeedScript statements into their SQL equivalents.
The DataServer then issues the SQL statements to the ODBC driver through the ODBC API.
The driver, which provides the software mechanisms for accessing and controlling the data
source, processes the SQL statements, transfers them to the data source manager, and returns
the results to OpenEdge through the ODBC API.
Note: The SQL presented in Figure 1–2 has been simplified for the purpose of focusing on
the data flow.
To facilitate the flow of statements between client and server, the DataServer places OpenEdge
equivalents for data definitions from a supported data source into a schema holder (a repository
for data definitions for one or more MS SQL Server data sources). When the OpenEdge client
or WebSpeed Agent executes statements and retrieves information from the data source, it relies
on data definitions in the schema holder.
Schema holder
As noted in the previous section, a schema holder contains information about the MS SQL
Server data sources. This information, called the schema of the data source, is a description of
its structure, its tables, the fields within its tables, and its indexes.
OpenEdge accesses the schema holder only when it compiles procedures and at the beginning
of a runtime session for schema caching (the loading of data definitions into memory).
Typically, the schema holder is not accessed during a runtime session after the initial schema
caching.
Before an OpenEdge client can access data in the MS SQL Server data source, you must create
a schema holder and load the required data source definitions into the schema holder. You can
then use the Data Dictionary to add OpenEdge database features such as validation expressions
and messages.
Figure 1–3 illustrates the schema-loading process.
OpenEdge schema holder
Cust_num INTEGER
Name CHARACTER
Max_credit DECIMAL
Figure 1–3: The schema-loading process
Data source
data definitions
Cust_nm INT
Name VARCHAR
Max_credit DECIMAL