什么是“简单明了的”SOA？

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!

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.

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".

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.

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.

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.

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

1. Similar feature were implemented several times

2. Data (e.g. customer or employee data) need to be shared between several applications

3. 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

1. No need to reimplement similar features over and over (e.g. provide a customer or employee service)

2. Facilitates integration of applications together and the access to common data or features

3. 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.

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.

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.

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.

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

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

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.

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.

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

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.

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:

1. Interface, Policy and Contract based
2. Location transparency
3. Autonomous
4. Abstract
5. Reusable
6. Composable
7. Stateless
8. Discoverable
9. Extensible
10. 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.

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.

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

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.