Middleware emergence

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Middleware emergence

• Distributed computing evolved from single-tier
  (terminal/mainframe) to 2-tier (client-server)to
  n-tier architecture
• To support heterogeneous environments open
  networking standards were introduced (i.e. OSI)
• How do we build/connect applications over a
  network?
• Answer middleware

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N-tier architecture

• More scalable architecture that separates
  processing to different servers

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What is Middleware?

• Middleware enables applications running across
  multiple platforms to communicate with each other
  .
• Middleware shields the developer from
  dependencies on Network Protocols, OS and
  hardware platforms.
• Middleware is a software layer that lies between
  the operating system and the applications on each
  site of the system.

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ODBC primitive middleware?

• Example of primitive middleware ODBC
• Client application is shielded from the details
  of the database implementation
• Not true middleware defines client side software
  only

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Types of Middleware

• Homegrown Middleware Solutions
• RPC (Remote Procedure Calls)
• Object-Oriented MW - ORB (Object Request Brokers)
• MOM (Message Oriented Middleware)
• Transaction Processing Monitors

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Homegrown Middleware

• Customized to meet specific needs
• Needs substantial investments
• Pros
• Can meet specific needs
• Cons
• Not cost effective
• Lacks scalability

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Remote Procedure calls

• Procedure/Function Oriented
• Follows the Request/Reply Model
• Mode of Communication is synchronous
• Provides Location/Platform transparency
• Technologies ONC RPC, DCE/RPC

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Object Oriented

• Language Independent
• Provides Location and Access transparency
• Mode of Communication is Synchronous
• Competing Standards (CORBA, DCOM, RMI)

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Message Oriented

• Data is transferred between applications as a
  message
• Mode Of Communication - Asynchronous
• Basic Components of MOM
• 1.Message (Information that needs to be
  transferred)
• 2.Queue (A container used to store and
  distribute messages)
• Types Of MOM
• 1. Message Queuing (Store and Forward)
• 2. Publish / Subscribe
• Products IBM WebSphere MQ, TIBCO Rendezvous

App-2
App-1
Queue
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Transaction Processing Monitors

• Transaction Processing Monitors are used for
  coordinating and monitoring the efforts of
  various application in a distributed environment.
• Products Tuxedo, IBM CICS, Microsoft Transaction
  Server

Client App
App1
TPM
App2
App3
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Property of Transactions

• Transaction is a collection of operations that
  should be treated as a single logical operation.
  
• To ensure reliable transactions ACID properties
  are needed

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Property of Transactions

• ACID properties
• A Atomicity either the entire set of operations
  happens or none of it does.

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Property of Transactions

• ACID properties
• A Atomicity either the entire set of operations
  happens or none of it does.
• C Consistency the set of operations taken
  together should move the system from one
  consistent state to another.

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Property of Transactions

• ACID properties
• A Atomicity either the entire set of operations
  happens or none of it does.
• C Consistency the set of operations taken
  together should move the system from one
  consistent state to another.
• I Isolation even though multiple transactions
  may operate concurrently, there is a total order
  on all transactions. Stated another way each
  transaction perceives the system as if no other
  transactions were running concurrently.

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Property of Transactions

• Transaction is a collection of operations that
  should be treated as a single logical operation.
• ACID properties
• A Atomicity either the entire set of operations
  happens or none of it does.
• C Consistency the set of operations taken
  together should move the system from one
  consistent state to another.
• I Isolation even though multiple transactions
  may operate concurrently, there is a total order
  on all transactions. Stated another way each
  transaction perceives the system as if no other
  transactions were running concurrently.
• D Durability even the face of a crash, once the
  system has said that a transaction completed, the
  results of the transaction must be permanent.

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Why Web Services?

• Lack of standardization in middleware
• Web services basic platform is available
  everywhere (XML, HTTP)
• Can serve as an integration tool for different
  business applications across organization
  boundaries without regards to what each business
  uses as the internal platform

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Why Web Services?

• Can serve as an integration tool for different
  business applications across organization
  boundaries without regards to what each business
  uses as the internal platform

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What are Web Services?

• Web services provide a standard means of
  interoperating between different software
  applications, running on a variety of platforms.

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Web Services

• Web services provide a standard means of
  interoperating between different software
  applications, running on a variety of platforms.
• W3C Working Group definitionA Web service is a
  software system designed to support interoperable
  machine-to-machine interaction over a network

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Web Services

• Web services provide a standard means of
  interoperating between different software
  applications, running on a variety of platforms.
• W3C Working Group definitionA Web service is a
  software system designed to support interoperable
  machine-to-machine interaction over a network. It
  has an interface described in a
  machine-processable format (specifically WSDL).

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Web Services

• Web services provide a standard means of
  interoperating between different software
  applications, running on a variety of platforms.
• W3C Working Group definitionA Web service is a
  software system designed to support interoperable
  machine-to-machine interaction over a network. It
  has an interface described in a
  machine-processable format (specifically WSDL).
  Other systems interact with the Web service in a
  manner prescribed by its description using SOAP
  messages, typically conveyed using HTTP with an
  XML serialization in conjunction with other
  Web-related standards

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Web Services

• Specifications for Web Services are defined as
  modules
• SOAP
• WSDL
• UDDI
• Basic platform is XML over HTTP

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Web Services
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XML

• Simple markup, data description language(based
  on SGML)
• Human-readable
• Customizable schema can be used to define
  atributes and elements
• XML can be used to created custom XML-based
  languages and services
• XML-based messages transported over HTTP serve as
  the basic platform for Web Services

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SOAP

• XML-based protocol defining message format
• One-way asynchronous technology
• Can use a variety of message passing styles RPC,
  publish/subscribe
• Primary underlying protocol is HTTP, but others
  can be used (SMTP)

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WSDL

• XML-based language
• Defines/describes Web services interfaces, data
  and message types, interaction patterns and
  protocol mappings

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UDDI

• Web Services Registry (of WSDL documents)
• Protocol for discovering and publishing Web
  Services
• UDDI registry is accessed by XML-based SOAP
  messages