IMS Connectivity in an On Demand Environment: A Practical Guide to IMS Connectivity

408 IMS Connectivity in an On Demand Environment: A Practical Guide to IMS Connectivity

Figure 21-2 The layered set of IMS Java class libraries

21.2.2 The basic concepts of relational access to hierarchical databases

In this section, we provide the basic concepts of relational access to the IMS hierarchical

database.

How to make a relational table from a segment

The solution to this problem is very simple. You can identify a type of segment occurrence as

a relational table. In this way, a type of segment relates to a type of relational table, a segment

occurrence relates to a row, and a field in a segment occurrence relates to a column in a

relational table. See Figure 21-3 for an example. The name of a segment becomes the table

name in an SQL query, and the name of a field becomes the column name in the SQL query.

Figure 21-3 Segment occurrences as relational tables

How to deal with the nature of hierarchy

Before coding your SQL to access IMS database, you need to understand another important

concept. As shown in Figure 21-3, the occurrences of segments have a hierarchical

relationship between a root segment and a dependent segment. Also, both the dependent

CEETDLI Interface

JNI

Base

App

DB

JDBC / SQL

XMS

DL/I

Database

View

IMS Java

Application

Customer Code

IMS Java Class Library

C layer Interface to IMS

Your Business Logic

IMS DB Metadata

by DL/I model Utility

IMS Dep. Region

TRX and Message

Processing

Mapping to

DL/I APIs

JDBC, JCA

interface

Java to C

Interface

XML Shredder,

XML Materializer

CUSTNO n NAME n ADDR n TELNO n

Root Segment

CUSTNO2 NAME2 ADDR2 TELNO2

CUSTNO1 NAME1 ADDR1 TELNO1

ORDNO m ORDNAME m

Dependent Segment A

ORDNO12 ORDNAME12

ORDNO11 ORDNAME11

PRODNO s PRODNAME s

PRODNO112 PRODNAME112

PRODNO111 PRODNAME111

Dependent Segment AA

TELNOnADDR nNAME nCUSTNO n

TELNO2ADDR2NAME2CUSTNO2

TELNO1ADDR1NAME1CUSTNO1

ORDNAME mORDNO m

ORDNAME12ORDNO12

ORDNAME11ORDNO11

PRODNAME sPRODNO s

PRODNAME112PRODNO112

PRODNAME111PRODNO111

Root Segment able

Dependent Segment A Table

Dependent Segment AA Table

ORDER

PRODUCT

CUSTOMER