Moving Forward with the On Demand Real-time Enterprise

242 Moving Forward with the On Demand Real-time Enterprise

5.2.3 DB2 MQ functions

DB2 provides a set of functions that allow us to read from and write to

WebSphere MQ Queues using SQL without having to learn the WebSphere MQ

Series application programming interface. These are implemented as a set of

user defined functions (UDFs). This means that the support is available to

applications that are written in any supported language that supports SQL. We

can use these functions in SQL stored procedures and even from a DB2

command interface.

The DB2 MQ functions allow us to support various messaging paradigms,

including Datagrams, Request/Reply and Publish/Subscribe. In the Datagram

paradigm, we just send or receive messages with no expectation of a reply being

generated. With a Request/Reply, when a message is sent, a reply is expected

and a correlation ID is used to associate the reply with the request when it arrives

back. With Publish/Subscribe, we just send a message to a topic and interested

parties subscribed to that topic will receive the message. There can be any

number of receivers for a topic.

In a basic configuration, a WebSphere MQ server is located on the database

server machine along with DB2. The WebSphere MQ functions are enabled to

DB2 and provide access to the WebSphere MQ server. DB2 clients can be

located on any machine accessible to the DB2 server. Multiple clients can

concurrently access the WebSphere MQ functions through the database.

Through the provided functions, DB2 clients can perform messaging operations

within SQL statements. These messaging operations allow DB2 applications to

communicate among themselves or with other WebSphere MQ applications.

The enable_MQFunctions command is used to enable a DB2 applications to use

the WebSphere MQ functions. It will automatically establish a simple default

configuration that client applications can use with no further administrative

action. The default configuration allows application programmers a quick way to

get started and a simpler interface for development. Additional functionality can

be configured incrementally as needed.

The Application Messaging Interface (AMI) of WebSphere MQ provides a clean

separation between messaging actions and the definitions that dictate how those

actions should be carried out. These definitions are kept in an external repository

file and managed using the AMI Administration tool. This makes AMI applications

simple to develop and maintain. The WebSphere MQ functions provided for DB2

UDB are based on the AMI WebSphere MQ interface. AMI supports the use of

an external configuration file, called the AMI Repository, to store configuration

information. The default configuration includes a WebSphere MQ AMI Repository

configured for use with DB2 UDB.