Modernizing IBM eServer iSeries Application Data Access - A Roadmap Cornerstone

58 Modernizing IBM Eserver iSeries Application Data Acess - A Roadmap Cornerstone

5.1 Introduction

The main goal of this stage is to minimize the impact of change on the business. This is

achieved in two ways:

򐂰 By de-coupling the database access from the application program.

򐂰 By utilizing SQL views as the only way to access the data. Adding new columns to the

database has no impact on existing views, thus eliminating the need to recreate the views

and supporting programs. These views can be accessed via service programs or directly

through ODBC or JDBC SQL statements.

The process involves a phased approach to replace native I/O operations with SQL data

access methods. The strategy of using I/O modules is to limit the SQL optimization

knowledge to the database programming group. This will allow the application programmers

to focus on solutions to business requirements without a need to understand the complexities

of database optimization.

The I/O module masks the complexity of the database from the application programmer. For

example, an HLL program may be performing several read operations to multiple files to fill a

subfile. This could be replaced by a single call to an I/O module that performs a single SQL

fetch operation to a join view and returns a single host array (multiple occurrence data

structure in RPG) to the caller.

In addition, the I/O module allows the database programmer to take advantage of database

functions (that is, date and time data types, variable length fields, identity columns, etc.), thus

eliminating many common HLL programming requirements. This includes programming

required to format date and time data, formatting address lines, etc. Figure 5-1 illustrates the

objective of this second stage.

Figure 5-1 Stage 2 - I/O modules to access SQL objects

The following is an overview of the steps required in this stage:

1. Establish naming conventions.

2. Create SQL views based on business requirements.

3. Create service programs to access data from the SQL views.

4. Convert selected legacy programs to use service programs.

Let us start explaining the different steps of this stage.

5.2 Establish naming conventions

One of the biggest issues in naming objects on the iSeries is the 10-character limitation of the

object name itself. Regardless of where the source resides you are still limited to 10

characters for the program and module objects. Because of the multitude of objects that can