CS Elective 2

• Middleware


  is any type of software that facilitates communication between two or more software systems
• Logical Middleware Model


  Depicts how information moves throughout the enterprise conceptually
• Physical Model

  • Depicts both the actual method of information
  • movement and the technology employed
• Middleware Models

  1. Logical Middleware Model
  2. Physical Model
• Point-to-Point Middleware

  • uses a simple pipe to allow one application to link to another application
  • Provide point-to-point connection between a source and a target application
• Many-to-Many Middleware


  Links many application to many other application
• Type of Communication Mechanisms

  • Asynchronous Mechanism
  • Synchronous Mechanism
• Asynchronous Mechanism


  moves information between one or many application in an asynchronous mode
• Synchronous Mechanism

  • Synchronous middleware mechanism is tightly coupled to applications
  • The applications are dependent on the middleware to process one or more function calls at a remote application
  • Calling application must halt processing to wait for the remote application to respond
• Communication Models

  • Connection-Oriented Communication
  • Connectionless Communication
  • Direct Communication
  • Fire and Forget
  • Queued Communication
  • Publish/ Subscribe
  • Request-Response
• Connection-Oriented Communication

  • Two parties connect, exchange messages and then disconnect
  • Typically, it is a synchronous process, but it can be asynchronous
• Connectionless Communication

  • Calling program does not enter a connection with the target process
  • Receiving application simply acts on the request, responding if required
• Direct Communication

  • The Middleware layer accepts the message from the calling program and passes it directly to the remote program
  • Usually synchronous in nature
• Fire and Forget

  • This model allows the middleware user to “fire off” a message and then “forget” about it
• Queued Communication

  • Generally requires a queue manager to place a message in a queue
• Publish/ Subscribe

  • Frees an application from the need to understand anything about the target application
• Request-Response

  • As name implies, a request is made to an application using request response middleware, and it responds to the request
• Types of Middleware

  • Remote Procedure Calls (RPC)
  • Message-Oriented Middleware (MOM)
  • Distributed Objects
  • Database-Oriented Middleware (DOM)
  • Transaction-Oriented Middleware (TOM)
  • Integration Servers
• Remote Procedure Calls (RPC)

  • Oldest type of middleware
  • Provide ability to invoke a function within one program and have that function execute within another program on a remote machine
  • RPC are synchronous
• Message-Oriented Middleware (MOM)

  • MOM is queuing software that uses is messages as a mechanism to move information from point to point
  • MOM uses the notion of messages to communicate between applications
  • MOM rely on asynchronous paradigm
• MOM supports two communication models

  • Point-to-Point
  • Message queuing (MQ)
• Distributed Objects


  Small application programs that use standard interfaces and protocols to communicate with one another
• two types of distributed objects

  • Common Object Request Broker Architecture (CORBA)
  • Component Object Model (COM)
• Database-Oriented Middleware (DOM)


  Facilitates communication with a database, whether from an application or between databases
• Transaction-Oriented Middleware (TOM)


  Provides mechanism for coordination information movement and method sharing between many different resources
• TOM-TP Monitors


  Provide mechanism to facilitate the communication between two or more applications as well as a location for application logic
• TOM-Application Servers


  Provide application logic sharing and processing and for connections to back-end resources
• TOM-Integration Servers


  Facilitates information movement between two or more resources and can account for differences in application semantics and platforms
• XML or Extensible Markup Language

  • provides a common-data exchange format, encapsulating both data and metadata
  • Promotes a self-defining message structure
• Elements


  Basic building blocks of an XML document
• Defined by tags

  Starting tag and an ending tag
• Root element


  Outermost element in the XML document
• XML support nested elements

  • elements within elements
  • This ability allows XML to support hierarchical structure
• Attributes of an element


  Describe characteristics of an elements in the beginning tag of an element
• Document Type Definition


  DTD
• XML Schema Definition


  XSD
• XML Query


  XQuery
• XML Path Language


  XPL
• Extensible Stylesheet Language Transformations


  XSLT
• XML document is created based on vocabulary of elements