Types of Middleware
• Remote procedure calls
• Message-oriented middleware
• Distributed objects
• Database-oriented middleware
• Transaction-oriented middleware
• Message brokers
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Message Oriented Middleware
• Message-Oriented Middleware (MOM) was
created to address some of the shortcomings of
RPCs (RMI) through the use of messaging.
• Like RPCs, MOM provides a standard API
across hardware, operating system platforms,
and networks.
• MOM is also able to guarantee that messages
will reach their destination, even when the
destination is not available (asynchronous
mode).
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Message-Oriented Middleware (2)
• The asynchronous model allows the application
to continue processing after making a
middleware service request. The message is
dispatched to queue manager, which makes
sure that the message is delivered to its final
destination.
• This asynchronous paradigm is much more
convenient for developers and users because it
does not block the application form processing
although the model is more complex.
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Message-Oriented Middleware (3)
• There are two models supported by the MOM:
– point-to-point (both systems must be active)
– message queuing (MQ, one end has to be active)
• MQ has several performance advantages over
the traditional RPCs
– each participating program proceeds on its own pace
without interruption from the middleware layer
– a program can publish the same the same message to
many remote programs without waiting the programs to
be up and running
– the queue manager can optimize the performance
through priorization, load balancing, and thread pooling
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Message-Oriented Middleware (4)
Message Brokers
• A message broker is a software system based
on asynchronous, store-and-forward messaging.
• It manages interactions between applications
and other information resources, utilizing
abstraction techniques.
• Simple operation: an application puts (publishes)
a message to the broker, another application
gets (subscribes to) the message. The
applications do not need to be session
connected.
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(Message Brokers, MQ)
• MQ is fairly fault tolerant in the cases of
network or system failure.
• Most MQ software lets the message be declared
as persistent or stored to disk during a commit at
certain intervals. This allows for recovery on
such situations.
• Each MQ product implements the notion of
messaging in its own way.
• Widely used commercial examples include IBM’s
MQSeries and Microsoft’s MSMQ.
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Message Brokers
• Any-to-any
The ability to connect diverse applications and other
information resources
– The consistency of the approach
– Common look-and-feel of all connected resources
• Many-to-many
– Once a resource is connected and publishing
information, the information is easily reusable by any
other application that requires it.
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Standard Features of Message
Brokers
• Message transformation engines
– Allow the message broker to alter the way
information is presented for each application.
• Intelligent routing capabilities
– Ability to identify a message, and an ability to
route them to appropriate location.
• Rules processing capabilities
– Ability to apply rules to the transformation and
routing of information.
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Services provided by Message
Brokers (or Integration servers)
• (A) Message transformation
• (B) Rules processing
• (C) Intelligent routing
• (D) Message warehousing and flow control
• (E) Repository services
• (F) Directory services
• (G) Management
• (H) APIs and adapters
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(A) Message Transformation Layer
• The message transformation layer understands
the format of all messages being passed among
the applications and transforms those messages
while they move.
• It provides a common dictionary that contains
information on how each application
communicates outside itself, as well as which
pieces of information have meaning to which
applications.
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Message Transformation Layer (2)
• Generally contain parsing and pattern-matching
methods that describe the structure of any
message format.
• Message formats are then constructed from
pieces that represent each field encapsulated
within a message.
• Once the message has been broken down to its
components parts, the fields may be recombined
to create a new message.
• Two kinds of transformations: schema
conversions and data conversions.
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Schema and Data Conversions
•A schema conversion is the process of changing
the structure of a message, and thus re-mapping
the schema, so that it is acceptable for the target
system.
• In other words, general re-mapping of data
formats.
•A data conversion is the process of determining
the data format of source and target
applications, assessing the differences between
them.
• That is, changes within an individual data field.
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(B) Rules Processing
• The rules processing engine provides the ability
to create rules to control the processing and
distribution of messages.
• It is an application development environment
supported by the message broker to address the
special requirements of integrating applications.
• By using rules engine, it becomes possible to
implement intelligent message routing and
transformation.
• The logic for sharing information.
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The Rules
• Most often, rules engines use traditional Boolean
logic (IF, ELSE, and OR) with an higher level
language to associate the rule with appropriate
actions.
• Generally relies on scripting languages rather
than more complex programming languages.
• The implementation of the rules generation
varies from entering commands to the broker to
Wizard-assisted management of rules
repositories.
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(C) Intelligent Routing
• A message broker can identify a message
coming from the source application and route it
to the proper target application, transforming it if
required.
• Builds on the capabilities of both the rules layer
and the message transformation layer.
• This happens virtually instantaneously, with as
many as a thousand of these operations
simultaneously.
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(D) Message Warehousing
• A message warehouse is a database that,
as an option, is able to store messages
that flow through the message broker.
• This feature is provided for
– Message mining
– Message integrity
– Message archiving
–Auditing
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Message Mining and Integrity
• Data mining
– Allows extraction of business data to support decision
making
– For example, the amount and characteristics of new
customer information processed through the broker
– Rules can be applied to alter the messages prior the
storing, e.g., for the data to make sense to business
users
• Message integrity
– A persistent buffer or queue for messages on the event of
system failures (or for other reasons)
– The messages may be resent or compared with other
warehouses on the network to insure integrity
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Message Archiving and Auditing
• Message archiving
– Ability to store months (or more) of message
traffic
– For auditing or other purposes
• Auditing
– Using the warehouse to determine the health
of the EAI solution
– One can monitor message traffic loads,
message content variations, the number of
messages requiring transformation, etc.
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(E) Repository Services
• A message broker repository is a database of information
about source and target applications.
• A sophisticated repository is capable of keeping track not
only rudimentary information (such as directory data),
but more sophisticated information about the systems:
– Location of system – Transformation information
– Security parameters – Design and architecture information
– Rules and logic for message – Object information
processing
– Message schema information
-- Metadata
– Enabling technology
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Value of the Repository
• A common reference point for all connected
processes and databases.
• Greatly simplifies integrating data and methods: it
is just about finding their equivalents and joining
them together.
• Possibility to track all the rules applied within the
EAI problem domain.
• By containing the schema of both source and
target system, it also contains information for
proper transformation of messages flowing from
source to target.
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(F) Directory Services
• Message brokers deal with distributed systems,
and thus require directory services to
– locate,
– identify,
–use, and
– authorize network resources for those systems
• Directory services provide a single point of entry
for applications and middleware – directories
know where to find resources on behalf of
applications.
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Directory Services (2)
• Directory services are nothing more than a way to classify
resources on the network in a way consistent with any
other method of classification.
• A multitude of widely available directory services exists:
– Domain Name System (DNS)
– Novell’s NetWare Directory System and Directory
Services
– Netscape Communications’ Directory Server
– Microsoft’s Active Directory
– X.500
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(G) Management
• Administration and management of the EAI
problem domain is primarily the responsibility of
the management layer of the message broker.
• General purpose management tools, such as
IBM Tivoli Framework, Microsoft Systems
Management Server, HP OpenView,
Novell ZENworks and CA Unicenter, lack
the ability to monitor message traffic, message
integrity, and the coordination of the distribution
of messages among target applications.
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(H) Adapters and APIs
• API is nothing more than the mechanism that allows an
application to access the services of a message broker.
• Adapters link deeply into an application without having to
invoke the native interfaces.
– Layers between the message broker interface and the
source or target application
– For example, set of libraries that map the differences
between two distinct interfaces
– Adapters for different source and target
applications(SAP R/3, Baan, Oracle, PeopleSoft,…)
– Adapters for certain types of databases (Oracle,
Sybase, DB2,..)
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Enterprise Service Bus
• Enterprise Service Bus
• Found in a category of middleware
infrastructure products usually based on Web
services standards, that provides foundational
services for more complex service-oriented
architectures via an event-driven and XML-
based messaging engine (the bus).
• An enterprise service bus generally provides
an abstraction layer on top of an Enterprise
Messaging System which allows integration
architects to exploit the value of messaging
without writing code.
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ESB common characteristics
1. it requires the clear separation of message headers and message body
2. it is usually operating system and language independent; it should work between Java and .Net
applications, for example
3. it (often) uses XML and Web services to transport messages
4. it includes adapter standards (such as J2C) for incorporating existing applications into the bus
5. it includes support for asynchronous processing
6. it includes intelligent, content-based routing
7. it includes a standardized security model to authorize, authenticate, and audit use of the ESB
8. it includes transformation services (such as XSLT) between the format of the sending application
and the receiving application, including the transformation of data formats
9. it includes validation against schemas for sending and receiving messages
10. it can uniformly apply business rules, enrichment of the message from other sources, splitting and
combining of multiple messages, and the handling of exceptions
11. it can conditionally route or transform messages based on a central policy
12. it is monitored for message latency and other characteristics described in a Service Level
Agreement
13. it (often) facilitates "service classes," responding appropriately to higher and lower priority users
14. it supports queuing, holding messages if applications are temporarily unavailable
15. it handles a "publish and subscribe" messaging model, including event handling
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ESB / XML
• An alternative view, particularly for high
performance enterprise service buses, is
that "standard" message formats should
flow across the bus, not just XML.
• Generating XML and parsing it can be
costly in terms of processing and memory,
and high volume scenarios may not be
viable.
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