What is SOA in plain english

Question

Can someone explain in plain english what is SOA all about  I hear SOA here  SOA there but I cannot understand exacly what it is and what is used for  Was it some simple concept and later evolved into something huge or what    All documents  including wiki are a bit abstract or maybe I m an idiot and don t get it  Is there an idiot s guide on this    What exactly is there behind these three letters

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As far as I understand  the basic concept there is that you create small  services  that provide something useful to other systems and avoid building large systems that tend to do everything inside the system    So you define a protocol which you will use for interaction  say  it might be SOAP web services  and let your  system-that-does-some-business-work  to interact with the small services to achieve your  big goal

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SOA or Service-Oriented Architecture is a software architecture pattern in which applications or systems are constructed from underlying  and usually distributed  software services that conform to a specific set of characteristics  namely    Interface  Policy and Contract based Location transparency Autonomous Abstract Reusable Composable Stateless Discoverable Extensible Loosely coupled   The primary goal of SOA is sofware development agility  i e  the ability to respond the change easily  and cheaply  thus allowing businesses to rapidly respond to changing markets   Services are typically  but by no means exclusively  implemented as web services  i e  they operate over the ubiquitous web HTTP protocol  and are implemented either using XML-based SOAP or the lightweight  and more popular  REST paradigm

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You might find this article  What is SOA  - SOA and Web Services Explained   helpful   A little teaser    SOA is a style of architecting applications in such a way that they are composed of discrete software agents that have simple  well defined interfaces and are orchestrated through a loose coupling to perform a required function  There are 2 roles in SOA- a service provider and a service consumer  A software agent may play both roles  SOA is not an entirely new concept     however  this article mainly focuses on SOA as implemented with web services

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I see many answers explaining a Service Oriented Architecture  SOA  using even more advanced words and technical terms  I d like to give a shot at explaining it for the layman  using an analogy in plain english     But first a description of a SOA SOA could be described in three layers as seen in the picture below  On one side we have the Provider and on the other side we have the Consumer  separated by a Bridge where the two sides communicate     The consumer uses a number of Applications necessary for it s business and the provider uses Components that provide these applications with information  They communicate through a set of Services using a common architecture          The analogy Imagine a house on the country side  that in many ways is part of a larger community  like a city or town  The city has it s own complex systems for providing water and electricity  handling sanitation  providing transportation and other utilities  The House is the consumer in this model  the City  or community  is the provider and the pipes  sewers  powerlines  optical fibers etc  is the Infrastructure in which they communicate     This model could loosely be compared to a SOA  The people in the house uses a number of different  applications  like radiators  computers  toilets  lamps  underfloor heating  bathtubs etc  These applications don t care how the city generates the water  creates the electricity or handles the waste as long as it works  The components of the city are generators  water pumps and sanitation areas  It provides the house with all these needs but it s up to the house to use it in what ever way it sees fit     I hope this gave at least someone a better picture of a SOA

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Reading the responses above  it sounds to me that SOA is what developers  good ones at least  have been doing from day one

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Let s assume you have four cooks  In SOA  you assume they hate each other  so you strive to let them have to talk to each other as little as possible   How do you do that  Well  you will first define the roles and interface -- cook 1 will make salad  cook 2 will make soup  cook 3 will make the steak  etc   Then you will place the dishes well organised on the table  so these are the interfaces  and say   Everybody please place your creation into your assigned dishes  Don t care about anybody else     This way  the four cooks have to talk to each other as little as possible  which is very good in software development -- not necessarily because they hate each other  but for other reasons like physical location  efficiency in making decisions etc     It also means you can recombine the dishes  services  as you like  For example  you might just use the dessert to service a cafe  or just take the soup and combine it with a bread you bought from another company to provide a cheaper menu  or let other restaurants use your salads to combine with their dishes  etc   One of the most successful implementation of SOA was at Amazon  Because of their design  they could re-package their whole infrastructure and sell it as Amazon Web Service      This is only one aspect of SOA

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SOA is acronym for Service Oriented Architecture      SOA is designing and writing software applications in such a way   that distinct software modules can be   integrated seamlessly with high degree   of re-usability           Most of the people   restrict SOA as writing client server   software-web-services  But it is too   small context of SOA  SOA is much   larger than that and over the past few   years web-services have been primary   medium of communcation which is   probably the reason why people think   of SOA as web-services in general   restricting the boundaries and meaning   of SOA    You can think of writing a database-access module which is so independent that it can work on its own without any dependencies  This module can expose classes which can be used by any host-software that needs database access  There s no start-up configuration in host-application  Whatever is needed or required is communicated through classes exposes by database-access module  We can call these classes as services and consider the module as service-enabled      Practicing SOA gives high degree of   re-usability by enforcing DRY  Don t   repeat your self  which results into   highly maintainable software    Maintainability is the first thing any   software architecture thinks of - SOA   gives you that

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Well You see   SOA stands for Service Oriented Architecture     In simplest words  you write a piece of code that is very generic i e  it does some thing that can be used in a lot of applications     may be something like a address book or may be a calculator   and you launch this code on the IIS   So you provide a service through your code   So you are a service provider   Now someone wants to use a similar code then he does not have to write the code again   He simply uses your code maybe through a web service   Hence he becomes a service consumer   Hence making a program using such services is called SOA   And the loose coupling is there as the service provider and consumer may be interacting even if they are using diff programming languages  Hope you understand

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SOA is a buzzword that was invented by technology vendors to help sell their Enterprise Service Bus related technologies  The idea is that you make your little island applications in the enterprise  eg  accounting system  stock control system  etc  all expose services  so that they can be orchestrated flexibly into  applications   or rather become parts of aggregate enterprise scoped business logic   Basically a load of old bollocks that nearly never works  because it misses the point that the reasons why technology is the way it is in an organisation is down to culture  evolution  history of the firm  and the lock in is so high that any attempt to restructure the technology is bound to fail

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Depends on who you are    If you re an business owner  SOA is a solution to increase your incomes and business agility  If you re an entreprise architect  SOA is a way to draw nice and clean piece of software on a blank canvas  If you re an architect SOA is the solution to design loosely coupled services over an integration platform  to just plug services into outlets  If you re a developper SOA is a programming paradigm where a service is in the center of the design and the code   You should read 100-SOA-Questions  pdf   Cheers

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Service Oriented Architecture  SOA  is a software architectural style that builds applications as a collection of pluggable parts  each of which can be reused by other applications

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what tends to happen in large organizations is that over time everything is either monolithic or disparate systems everywhere or a little of both   Someone eventually comes in and says we ve got a mess   Now  you want to re-design  money to someone  everything to be oriented in a sort of monotlithic depends on who you pay paradigm but at the same time be able to add pieces and parts independently of the master monolith   So you buy Oracle s SOA and Oracle becomes the boss of all your parts   All the other players coming in have to work with SOA via a service  web service or whatever it has    The Oracle monolith takes care of everything  monolith is not meant derogatory    Oh yeah  you got ASP NET MVC on the front or something else   main thing is moving things in and out of they system without impact and keeping the vendor Oracle SOA  Microsoft WCF  as the brains of it all   everything s all oop ood like  fluid  things moving in and out with little to no impact  even human services  not just computers   To me it just means a bunch of web services  or whatever we call them in the future  with a good front end   And if you own the database just hit the database and stop worrying about buzzwords   it s okay

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It could also stand for  Struct of Arrays   as opposed to  Array of Structs   which is a common topic in parallel  especially SIMD  programming  but I m guessing that s not what you mean here

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SOA is a new badge for some very old ideas    Divide your code into reusable modules  Encapsulate in a module any design decision that is likely to change  Design your modules in such a way that they can be combined in different useful ways  sometimes called a  family  or  product line      These are all bedrock software-development principles  many of them first articulated by David Parnas   What s new in SOA is   You re doing it on a network  Modules are communicating by sending messages to each other over the network  rather than by more tradtional programming-language mechanisms like procedure calls   In particular  in a service-oriented architecture the parts generally don t share mutable state  global variables in a traditional program    Or if they do share state  that state is carefully locked up in a database which is itself an agent and which can easily manage multiple concurrent clients

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A traditional application architecture is    A user interface Undefined stuff  implementation  that s encapsulated hidden behind the user interface   If you want to access the data programmatically  you might need to resort to screen-scraping   SOA seems to me to be an architecture which focus on exposing machine-readable data and or APIs  instead of on exposing UIs

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SOA is an architectural style but also a vision on how heterogeneous application should be developped and integrated  The main purpose of SOA is to shift away from monolithic applications and have instead a set of reusable services that can be composed to build applications    IMHO  SOA makes sense only at the enterprise-level  and means nothing for a single application    In many enterprise  each department had its own set of enterprise applications which implied    Similar feature were implemented several times Data  e g  customer or employee data  need to be shared between several applications Applications were department-centric    With SOA  the idea is to have reusable services be made available enterprise-wide  so that application can be built and composed out of them  The promise of SOA are    No need to reimplement similar features over and over  e g  provide a customer or employee service  Facilitates integration of applications together and the access to common data or features  Enterprise-centric development     effort    The SOA vision requires an technological shift as well as an organizational shift  Whereas it solves some problem  it also introduces other  for instance security is much harder with SOA that with monolithic application  Therefore SOA is subject to discussion on whether it works or not   This is the 1000ft view of SOA  It however doesn t stop here  There are other concepts complementing SOA such as business process orchestration  BPM   enterprise service bus  ESB   complex event processing  CEP   etc  They all tackle the problem of IT business alignement  that is  how to have the IT be able to support the business effectively

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from ittoolbox blogs   The following outlines the similarities and differences to past design techniques       SOA versus Structured Programming  o Similarities  Most similar to subroutine calls where parameters are passed and the operation of the function is abstracted from the caller - e g  CICS link and execute and the COBOL CALL reserved word  Copybooks are used to define data structure which is typically defined as an XML schema for services   o Differences  SOA is loosely coupled implying changes to a service have less impact to the consumer  the  calling  program  and services are interoperable across languages and platforms        SOA versus OOA OOD  o Similarities  Encapsulation  Abstraction and Defined Interfaces  o Differences  SOA is loosely coupled with no class hierarchy or inheritance  Low-level abstractions - class level versus business service       SOA versus legacy Component Based Development  CBD  - e g  CORBA  DCOM  EJB o Similarities  Reuse through assembling components  Interfaces  Remote calls  o Differences  Wide adoption of standards  XML Schemas vs  Marshaled Objects  Service Orchestration  Designing for reuse is easier  services are business focused vs  IT focused  business services are course grained  broad in scope        SOA  for integration  versus Enterprise Application Integration  EAI   o Similarities  Best practices  well defined interfaces  standardized schemas  event driven architecture   reusable interfaces  common schemas  o Differences  Standards  adoption  and improved tools

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I would suggest you read articles by Thomas Erl and Roger Sessions  this will give you a firm handle on what SOA is all about  These are also good resources  look at the SOA explained for your boss one for a layman explanation  Building a SOA  SOA Design Pattern  Achieving integrity in a SOA  Why your SOA should be like a VW Beetle  SOA explained for your boss  WCF Service Performance

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Have a listen to this week s edition of the Floss Weekly podcast  which covers SOA  The descriptions are pretty high level and don t delve into too many technical details  although more concrete and recognizable examples of SOA projects would have been helpful

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Only one suggestion -  Read SOA Concepts  Technology and Design by Thomas Erl    It has very beautifully given the details about SOA in plain English and with case studies

[soa] What is SOA "in plain english"?

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