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Introduction

The following sections introduce the Oracle Message Broker and its features:

What is the Oracle Message Broker?

Oracle Message Broker plays a major role in Oracle's solution for Enterprise Application Integration (EAI). It is a scalable and open platform ideal for integrating strategic applications, e-commerce, or legacy systems.

The Oracle Message Broker provides an open, asynchronous, system-independent, message-based communication mechanism. The foundation of the Oracle Message Broker is an implementation of the Java Message Service API. Oracle Message Broker allows different applications or systems to interact in a near real-time, robust, reliable, and scalable manner to complete end-to-end cross-functional business processes. A message selection engine supports message routing based on the contents of a message header, and transactions are supported across application boundaries.

The Oracle Message Broker integrates applications on the business process level that work across the enterprise. While integrating applications, the Oracle Message Broker shields you from the complicated underlying messaging technology. Because of its interoperability with a complete line of Oracle products, and with the leading commercial messaging products, the Oracle Message Broker seamlessly integrates applications and leverages existing technology.

What is JMS?

The Oracle Message Broker implements an important and powerful standard called the Java Message Service (JMS)¹. The Oracle Message Broker implementation of JMS supports many of the existing Message Oriented Middleware (MOM) solutions. The JMS API is a standard developed by Sun Microsystems, Inc. to support enterprise messaging. JMS provides a standards based API for writing distributed applications. Enterprise messaging using JMS provides a reliable, flexible service for the asynchronous exchange of critical business data and events throughout an enterprise.

Refer to the Java Message Service documentation and the Java Message Service specification available from Javasoft at the following site for more information on JMS:

http://www.javasoft.com/products/jms

Oracle Message Broker Components

The Oracle Message Broker consists of the following components:

Figure 1-1 shows the Oracle Message Broker's important components.

Figure 1-1 Oracle Message Broker Architecture

Oracle Message Broker Core

The Oracle Message Broker Core is a JMS provider². A JMS provider implements the JMS API that allows you to use JMS for messaging in the enterprise, with one or more Oracle Message Brokers communicating and coordinating message transmission. The Oracle Message Broker Core provides:

Support for pushing messages to clients
Polling of message servers that do not support notification
Handling of certain administrative tasks
Multiplexing JMS clients onto the underlying message servers

The Oracle Message Broker Core also communicates with message servers using a standard driver interface that is transparent to client applications.

Drivers and Message Servers

Oracle Message Broker drivers provide access to proprietary message servers. Message servers manage and store messages. Drivers also coordinate message translation to native storage formats. Native storage formats are the formats that messages are stored in on a message server, when the message server does not directly support JMS.

Table 1-1 shows the drivers that support message servers in Oracle Message Broker.

Table 1-1 Oracle Message Broker Drivers

Driver	Underlying Message Server
Oracle Advanced Queuing (AQ) Driver	Supports persistent delivery of JMS messages using the Oracle 8i Database with the Advanced Queuing (AQ) messaging infrastructure.
Oracle AQ Lite Driver	Supports persistent delivery of JMS messages using Oracle 8i Lite and the AQ Lite messaging infrastructure.
Oracle Volatile Driver	Provides very fast delivery of JMS messages using lightweight, in-memory, communication facilities. The Volatile Driver is useful for high throughput of messages when the messaging system does not require persistent message storage.
MQSeries Driver	Supports commercial messaging system based on IBM MQSeries V5.1.
Oracle Multicast Driver	Supports very fast delivery of JMS messages using lightweight, multicast communication facilities. The Multicast Driver uses the Oracle Application Server Multicast Communication libraries.
TIBCO Driver	Provides very fast delivery of transient messages based on lightweight multicast communication facilities.The TIB/Rendezvous (TIBCO) Driver is based on TIB/Rendezvous Release 5.x, or TIB/Rendezvous Pro Release 5.x.

Administrative Components

The Oracle Message Broker supports two options for specifying configuration information for administration:

LDAP Directory Configuration
Lightweight Configuration

See "Configuration Options" for a summary of the features of the configuration options.

The configuration information for an LDAP Directory is modified using the administrative utilities. See "Administration and Monitoring Utilities" for information on the Oracle Message Broker utilities.

What is an OMB Instance

An OMB Instance defines the configuration information used by an active process running the Oracle Message Broker (an instance of the Oracle Message Broker). The configuration information is stored, either in the form of LDAP Directory entries or using the Lightweight configuration facilities. The information that defines an OMB Instance includes parameters used to configure the Oracle Message Broker process, the connection factories that JMS clients use to establish a connection with the Oracle Message Broker, and the configuration information that the Oracle Message Broker requires to connect to a queue or topic.

Using an LDAP Directory for configuration, the entries that define an OMB instance are unique for that instance and are not shared by other OMB instances. However, these entries may contain references to a physical entity that is commonly used by more than one OMB Instance. For example, from an administrative standpoint, OMB destinations, including queues and topics, are aliases for an object that is managed by a message server that stores messages. This allows different OMB destination objects to refer to the same queue or topic on the message store.

Client Programming Interface

The Oracle Message Broker client programming interface lets client programs communicate with the Oracle Message Broker. The Oracle Message Broker supports the following client programming interfaces:

The JMS API for Java program access (see Chapter 3, "JMS Programming" for more information on this client programming interface)
A C++ API that is similar to the JMS API (see Chapter 9, "Oracle Message Broker C++ API" for more information on this client programming interface)
PL/SQL Operational Interface

PL/SQL Operational Interface

The Oracle Message Broker provides an AQ Driver specific PL/SQL package. The PL/SQL package is an easy to use mechanism for enqueueing and dequeueing JMS messages directly to and from Oracle AQ queues. The Oracle AQ queue used for this purpose needs to be created using the Oracle Message Broker administrative utilities. The PL/SQL package eliminates the need for PL/SQL applications running within the Database Server to use the JMS Java or C++ client interfaces to pass messages to and from Oracle AQ queues.

A message placed on an Oracle AQ queue using the PL/SQL package can be propagated between Oracle Message Brokers, or to any of the supported Oracle Message Broker drivers, including the following drivers: Oracle Volatile, IBM MQSeries, TIB/Rendezvous, or Oracle Multicast.

Legacy applications written in PL/SQL can easily be integrated using the Oracle Message Broker and the PL/SQL package. This deployment option supports the following environments:

Developers using PL/SQL
A hub and spoke architecture where the hub is based on AQ and PL/SQL

The following list includes some of the advantages of using the PL/SQL package:

Only two PL/SQL subroutines are necessary to either enqueue or dequeue a message
Efficiency - enqueues and dequeues are performed within the context of the Database Server using PL/SQL
Support for advanced features - including propagation and message selection, are available through the Oracle Message Broker

Refer to "Using the PL/SQL Operational Interface" for more information on the PL/SQL operational interface.

Oracle Message Broker Features

The Oracle Message Broker provides a complete set of messaging features. Table 1-2 lists some of the Oracle Message Broker features.

Table 1-2 Oracle Message Broker Features

Feature	Description
JMS publish/subscribe model	The publish/subscribe model is a development and deployment model well suited for integrating loosely-coupled applications. Using the publish/subscribe model, subscribers specify their interest in messages using content-based topics.
JMS point-to-point (PTP) model	The Oracle Message Broker supports the point-to-point messaging model. This model is useful for message delivery to a single destination.
Persistent JMS Delivery Mode	The Oracle AQ Driver, the AQ Lite Driver, and the IBM MQSeries Driver support persistent message delivery. Using persistent message delivery, the Oracle Message Broker leverages Oracle AQ, Oracle AQ Lite, or IBM MQSeries to log messages to stable storage as part of the message-send operation. This insures that messages are not lost during message propagation, or in the event of system failures.
Non-persistent Delivery Mode	Non-persistent delivery mode is supported for Volatile, Multicast, TIBCO/Rendezvous, and MQSeries drivers. A Non-persistent message is handled with an at-most-once delivery guarantee.
Volatile Queues	Volatile queues offer the following benefits: High speed transaction processing A Transient state with a short lifetime - messages are kept for the duration of an active Oracle Message Broker Low overhead - the maintenance infrastructure for recoverability and persistence is not required Flexibility - can be used for both transaction oriented processing and inter-process communication
Scalability	The service oriented approach combined with excellent thread management provides an inherently scalable architecture. The Oracle Message Broker can push messages to clients with a connection required only for the duration of the delivery of the message. Supporting push based clients, a single Oracle Message Broker can support a large number of clients.
Oracle Message Broker Interoperability	Provides a rich messaging mechanism, in terms of both message type and models, over widely adopted message queuing systems. This feature protects corporate investments by leveraging existing messaging systems. Users can write their API code once, and deploy it over several messaging systems. The Oracle Message Broker is designed to provide a functionally rich messaging model over a number of industry queuing systems, including: Oracle Advanced Queuing Oracle AQ Lite IBM MQSeries TIBCO Rendezvous Integrated drivers for these queuing systems ensure a base level of transparency over any given queuing system.
Platform Independence	Allows communication to a wide variety of operating system platforms. The Oracle Message Broker can talk to any of its supported messaging systems on several supported heterogeneous platforms.
Industry Standard Programming Interface	Adherence to the JMS specification provides a standards based approach, with minimal complexity.

Administration and Monitoring Utilities

This section introduces the utilities for managing the Oracle Message Broker. These utilities include:

Command Line Tools

The Oracle Message Broker includes the following administration and monitoring utilities:

A command line tool, AdminUtil for Oracle Message Broker administration This connects to an LDAP Directory and allows an administrator to create, delete, and manage Oracle Message Broker configuration information. The command operates in either interactive mode or batch mode. In interactive mode an administrator enters commands at an input prompt. In batch mode the utility processes files containing stored commands
A command line tool, AdminDirCheck, for checking and validating Oracle Message Broker directory entries. This performs basic validation for Oracle Message Broker configuration data. It checks and validates Oracle Message Broker entries stored in the LDAP Directory.
A command line tool, Migrate10To20, for migrating Oracle Message Broker directory entries from older versions.

Graphical User Interface

The Oracle Message Broker provides an easy to use Graphical User Interface (GUI) that allows an administrator to modify administrative entries stored in the LDAP Directory. The GUI helps an administrator set up an Oracle Message Broker and provides a view of an active Oracle Message Broker's configuration. Using the GUI, an administrator can easily view, create, delete, and manage Oracle Message Broker configuration information.

Performance Monitoring Service

Oracle Message Broker optionally can collect performance metrics so that an administrator can dynamically monitor system performance. The Oracle Message Broker performance metrics are available using the Dynamic Monitoring Service (DMS). The Oracle Message Broker includes a command line tool to save DMS metrics. Refer to Chapter 6, "Oracle Message Broker Extensions" for more information on working with the performance monitoring information.

Oracle Message Broker Deployment Options

This section summarizes the deployment options available for running the Oracle Message Broker. The available configuration options are:

In addition, there are two operation modes for the Oracle Message Broker:

There are four possible deployment options for an Oracle Message Broker application:

Using the LDAP Directory in Local Mode.
Using the LDAP Directory in Remote Mode.
Using Lightweight Configuration in Local Mode.
Using Lightweight Configuration in Remote Mode.

Choosing from these four available options for running the Oracle Message Broker, it is up to you to select the option that best meets your needs.

Configuration Options

Selecting a configuration option for the Oracle Message Broker allows you to choose between the following:

Using LDAP Directory Configuration

Using an LDAP Directory for administrative information allows for an open, standards based access protocol for system management and configuration. LDAP Directory configuration requires an LDAP Directory installation and the directory must be configured for operation with Oracle Message Broker. This configuration option provides location independence for Oracle Message Broker configuration information. LDAP Directory configuration also provides the following:

Configuration files do not need to be stored locally
A scripting language is available to modify configuration data
A GUI is provided to modify configuration data
Dynamic updates to configuration data are supported for Oracle Message Broker executing in Remote Mode
Provides security services, including access control
Support for Oracle Message Broker Propagation
Provides location independence for Oracle Message Broker clients to access remote Oracle Message Brokers
Supports durable storage of durable subscribers and message selectors for durable subscribers.

For more information on configuration using an LDAP Directory, refer to Chapter 4, "Administration".

Using Lightweight Configuration

With lightweight configuration, the Oracle Message Broker reads configuration information from a file or from Java properties when it begins its execution. The Oracle Message Broker configuration information specifies the names and configuration options for all administrative objects, such as the names and types of JMS destinations (topics or queues). Lightweight configuration provides the following:

Simple configuration using either Java properties or a stored information from a configuration file.
Lightweight configuration does not require an LDAP Directory.
Methods for starting the AQ Driver using minimal configuration options, by providing only a since a service name, a username, and a password.
Better availability (a running LDAP server available is not required).

For more information on configuration using an Lightweight Configuration, refer to Chapter 13, "Lightweight Configuration".

Operation Modes

The Oracle Message Broker allows you to choose between the following operation modes:

Local Mode

A Local Mode Oracle Message Broker runs within the same process as the Oracle Message Broker client. When running in local operation mode, the Oracle Message Broker uses local procedure calls to interact with the Oracle Message Broker client (the Local Mode Oracle Message Broker does not start an ORB). Thus, in Local Mode, Oracle Message Broker clients can use ORBs for their own purposes.

Operation in Local Mode has the following characteristics:

Performance is usually better when running in Local Mode. In Local Mode the Oracle Message Broker client requests do not have to pass through a separate process to access drivers, including Oracle AQ, MQSeries, or another driver.
Availability is easier to manage in Local Mode. There is no need to keep a separate Oracle Message Broker process available.
The Volatile Driver is of limited use in Local Mode. The Volatile Driver is more useful in Remote Mode when different clients can connect to the Oracle Message Broker and use the Volatile Driver as a destination separate from the client (in Local Mode, clients can only access the Oracle Message Broker within a single process, and all clients must run within the same process).
Oracle Message Broker Propagation is not supported in Local Mode.
If the security service is used within a Local Mode Oracle Message Broker, an Oracle Message Broker developer can write code that changes any decisions made by the security service.

For more information on Local Mode, refer to "Running in Local Mode".

Remote Mode

A Remote Mode (Non-Local Mode) Oracle Message Broker communicates with Oracle Message Broker clients using IIOP. A Remote Mode Oracle Message Broker runs in a separate process from Oracle Message Broker clients. However, it is possible to run a Remote Mode Oracle Message Broker in the same process and communicate using IIOP.

Operation in Remote Mode has the following characteristics:

Remote Mode Oracle Message Brokers support Oracle Message Broker Propagation.
Remote Mode Oracle Message Brokers support the security service for access control.
A Remote Oracle Message Broker can be configured to start the AQ Driver with a Database Server password that the Oracle Message Broker administrator does not want to expose to Oracle Message Broker clients.
If Oracle Message Broker clients use a Remote Mode Oracle Message Broker to access Oracle AQ, then they will only be able to access Oracle AQ in a manner that is authenticated and authorized by the security service. That is, these clients will only not be able to use the Database Server username/password for general purpose Database Server access.
Oracle Message Broker clients that use the Volatile Driver are most useful when running the Oracle Message Broker in Remote Mode.

For more information on Remote Mode, refer to "Running in Remote Mode".

¹ The Oracle Message Broker implements the JMS specification with some restrictions, and with limitations based on the selected driver. The Oracle Message Broker Release Notes, and Chapter 7, "Message Servers and Drivers" describe JMS features, limitations, and restrictions. When we refer to the Oracle Message Broker implementation of JMS or refer to the Oracle Message Broker as a JMS provider throughout this guide, we acknowledge these limitations.
² The Oracle Message Broker implements the JMS specification with general restrictions, and with restrictions based on the selected driver. The Oracle Message Broker Release Notes, and Chapter 7, "Message Servers and Drivers" describe JMS features, limitations, and restrictions.

1 Introduction