Application Integration Technology

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Application Integration Technology

• IT 490

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Middleware Basics

• Middleware provides a mechanism that allows one
  entity (application or database) to communicate
  with another entity or entities.
• Middleware is the best hope for moving
  information between applications and databases.
  Unfortunately, traditional middleware as it
  exists today (Remote Procedure Calls RPCs,
  Message Oriented Middleware-MOM) can provide
  connections between applications, but in order to
  facilitate the use of middleware, changes to the
  source and target systems become unmanageable and
  inflexible.

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Middleware Basics

• New types of middleware came into play, including
  application servers and message brokers.
• As a definition, middleware is basically any type
  of software that facilitates communications
  between two or more software systems.

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• Types of Middleware
• RPCs ? the oldest type of middleware but they are
  the easiest to understand and use. Basically RPCs
  provide developers with the ability to invoke a
  function within one program and have that
  function actually execute within another program
  or another remote machine

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• RPCs are synchronous. They stop the execution of
  the program in order to carry out remote
  procedure calls. Because of this, RPCs are also
  knows as blocking middleware.
• Because carrying out a remote procedure call
  requires a lot of overhead in the systems, RPCs
  require more bandwidth than any other types of
  middleware.
• Fig. 7.2 RPCs Local Functions Executing
  on Remote Machines

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• The best known type of RPC is Distributed
  Computing Environment (DCE) from Open Software
  Foundation (OSF). It provides a very
  sophisticated distributed RPC mechanism with many
  layers of services (such as security services,
  directory services, and the ability to maintain
  integrity between applications).
• DCE requires a lot of overhead so the performance
  of such system is very poor.
• The main RPC advantage is the simplicity of the
  systems and integration. The main disadvantage is
  their requirement for more processing power.
• RPCs require anywhere from 10,000 to 15,000
  instructions in order to process a remote
  request. All these add to the cost of the
  overhead.

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• Message-Oriented ? MOM was created to address
  some shortcomings of RPCs through the use of
  messaging. Traditional MOM is typically queuing
  software, using messages as a mechanism to move
  information from point to point.
• Because MOM uses the notion of messages to
  communicate between applications, direct coupling
  with the middleware mechanism and the application
  is not required.

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• MOM products use an asynchronous paradigm and
  because its decoupled from the application, they
  allow the application to function independently.
• The asynchronous paradigm is much more convenient
  for developers and users because it does not
  block the application from processing, although
  the model is a bit more complex than the
  synchronous model.

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• MOM is able to ensure delivery of a message from
  one application to the next through several
  sophisticated mechanisms, such as message
  persistence.
• The use of messages is also an advantage because
  messages are small byte-sized units of
  information that move between applications.

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• Messages have a schema (structure) and data
  (content).
• There are two models supported by MOM
• Point-to-Point
• Message Queuing (MQ) ? this has several
  advantages over standard RPCs. First of all MQ
  lets each participating program proceed at its
  own pace without interruption from the middleware
  layer. Another benefit to MQ is that the program
  can broadcast the same message to many remote
  programs without waiting for the remote programs
  to be up and running.

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• Distributed-Objects ? are also considered
  middleware because they facilitate
  inter-application communications. But at the same
  time they are also mechanisms for applications
  development, providing enabling technology for
  enterprise-wide method sharing.
• Distributed Objects are really small application
  programs that use standard interfaces and
  protocols to communicate with one another

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• There are 2 types of distributed objects on the
  market today CORBA (created by OMG in 1991 is
  more of a standard than a technology) and COM
  (created by Microsoft, is a distributed object
  standard). Just like CORBA, COM provides rules
  for developers when creating COM-enabled
  distributed objects.

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• - Database-Oriented ? is any middleware that
  facilitates communications with a database,
  whether from an application or between databases.
  Developers use them as a mechanism to extract
  information from either local or remote
  databases.

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• They work with 2 basic database types
• call-level interface (CLI)
• at-native database middleware
• While CLIs provide access to any number of
  databases through a well defined common interface
  and are common APIs that span several types of
  database, they work most typically with
  relational databases (for example Microsofts
  ODBC)
• Fig. 7.6
  Microsofts OLE DB

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• Transaction-Oriented ? (for example TP monitors
  and application servers) do a pretty good job at
  coordinating information movement and method
  sharing between many different resources.
  Typically it creates a tightly coupled EAI
  solution, where messaging solutions are more
  cohesive in nature. In addition, the source and
  target applications will have to be changed to
  take advantage of this transactional middleware.
• TP Monitors ? are the first generation
  applications servers and a transactional
  middleware product. They provide a location for
  application logic in addition to a mechanism to
  facilitate the communication between 2 or more
  applications
• TP monitors are based on the premise of a
  transaction ? is a unit of work with a beginning
  and an end. The reasoning is that if application
  logic is encapsulated within a transaction, then
  the transaction either completes or is rolled
  back completely.

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• An advantage of using transactions is the ability
  to break an application into smaller portions and
  then invoke those transactions to carry out the
  binding of the user or another connected system.
• TP monitors provide connectors that allow them to
  connect to resources such as databases, other
  applications and queues.
• TP monitors provide queuing, routing and
  messaging features all of which enable
  distributed application developers to bypass the
  TP monitors transactional features. As a result
  priorities can be assigned to classes of
  messages, letting the higher messages receive
  server resources first.
• TP monitors real performance value is in their
  load-balancing feature, which allows them to
  respond gracefully to a barrage of transactions.

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• Application Servers ? is not new but is the
  fastest growing segment of the middleware
  marketplace and its defined by the many new
  products calling themselves applications
  servers.
• Most Application Servers are employed as
  Web-enabled middleware, processing transactions
  from web-enabled applications. They also employ
  Java rather than traditional procedural languages
  like C or COBOL (which are common with TP
  monitors)
• Application Servers are servers that not only
  provide for the sharing and processing of
  application logic, but they also provide
  connections to back-end resources.
• These resources include databases, ERP
  applications and even traditional mainframe
  applications. They also provide user interface
  development mechanisms.

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• - Message Brokers ? can facilitate information
  movement between two or more resources (source or
  target applications) and can account for the
  difference in application semantics and
  platforms.
• Message Brokers can also join many applications
  using common rules and routing engines. They can
  transform the schema and content of the
  information as it flows between various
  applications and databases.

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• Middleware Models
• The Logical Middleware Model ? depicts how the
  information moves throughout the enterprise
  conceptually.
• The Physical Middleware Model ? depicts how the
  information actually moves and the technology it
  employs.
• There are a few messaging models we will look at
  in order to understand the physical middleware
  model
• One-to-One vs Many-to-Many ? Middleware can work
  in a point-to-point as well as many-to many
  configurations
• 1. Point-to-Point Middleware ? allows one
  application to link to one other application via
  a simple pipe. When communication is desired, the
  two applications communicate via the pipe using a
  procedure call or message (see Fig. 7.10)

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• While it is possible at this time to connect
  together more than 2 applications using
  traditional point-to-point middleware, doing so
  will generate a chaos inside the network because
  of the redundant point to point connections

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• Many-to-Many Middleware ? links multiple
  applications to many other applications. Thats
  why this is the best fit for EAI and is the
  current trend in the EAI world. It is also the
  most powerful logic middleware model in that it
  provides both flexibility and applicability to
  the EAI problem domain.

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• 3. Synchronous vs. Asynchronous
• Asynchronous Middleware moves information between
  one or many applications in an asynchronous
  mode-that is, the middleware software is able to
  decouple itself from the source or target
  applications and the applications are not
  dependent on the other connected applications for
  processing. A major advantage is that the
  middleware will not block the application for
  processing.
• Synchronous Middleware is tightly coupled to
  applications and the applications are dependent
  on the middleware to process one or more function
  calls at a remote application. As a result the
  calling application must halt processing in order
  to wait for the remote application to respond?
  this is called blocking middleware.

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• 4. Connection-Oriented and Connectionless
• Connection-oriented communications ? two parties
  connect, exchange messages and then disconnect.
  This is a synchronous process usually but
  sometimes can be asynchronous.
• Connectionless communications ? the calling
  program does not enter into a connection with the
  target process.