What came before web services and SOA?_问答_开发者

I'm interested in the history of distributed, coll开发者_如何学编程aborative, cross-organisational programming paradigms - web services and SOA are de-facto now, but what came before? What models have been superceded by SOA?

Thanks

Well, I suppose there was RPC - which is really what SOAP is, only they didn't piggy-back the data payload on top of a standard protocol (http in SOAP's case). So CORBA and DCE-RPC and ONC RPC all did the same thing, but only over internal networks, not over the internet.

There was also EDI as a 'standard' for exchanging data between disparate entities. This was effectively a way of defining what the data payload would look like (similar the the XML part of SOAP).

But these are still not SOAs really, they provide the same functionality but the big difference was how people thought of using them. Once you could write a machine-to-machine 'website' and have different machines talk to each other through them, it took off. You could do it before using CORBA, say, but it wasn't as easy or as widely known about. You can tell this has happened by the fact we have several terms used for effectively the same thing - SOA, SaaS, Web Services... all the same thing (but lots of money to be made 'consulting' on the difference ;) )

Maybe Silos?

...where services are just not shared across an enterprise, at least in a standard way. This is why products like BizTalk are used: to get silos to talk to each other via standard interfaces.

I don't really think you'll find anything that's been superceded by SOA. You will find that there's been progress in organizing computer programs to take advantage of the SOA type principles. As for programming models that have been in reasonably common use, well, let's see... CORBA, RPC, more generic client-server applications. Of course, computer-to-computer communications were preceded by process-to-process communication using a wide variety of conventions.

SOA as a philosophy of breaking large problems into smaller ones and then composing the results has been known and applied since humans started making bricks instead of building complete walls. Of course, that was mostly implicit. Explicit statements for SOA really started to come about with CORBA and, while SOA is independent of Web Services, the advent of HTTP and XML, and then SOAP, really started to make development of non-specialized "services" easier, more worthwhile and thus common.

This pdf A Note on Distributed Computing should be an interesting read. It is pre-SOA and would give an idea of the history up to that point (1994).

I would say distributed object technology. And before it remote procedure calls. RPC is one of the earlier approaches and gained popularity from the Sun implementation. One of the famous uses is NFS (network file system).

As object oriented programming became more popular, distributed objects followed. Most important was Microsoft DCOM (and later COM+) and, more industry wide, CORBA.

SOA is a divide and conquer approach that is critically dependent on the concept of services. Which is different from objects as used by CORBA et al, as well as being different from resources as in REST.

Objects are created and their lifetime is typically controlled by the client. On the other hand, services are assumed to be always there provided by the server. This is one reason why SOA is not equivalent to distributed objects.

Services are also stateless, which means that the server when considering the response to a service request need not look at the history of interaction with the client. This was not a consideration when originally devising the RPC concept as scalability wasn't such an important issue then. Interestingly, large scale users of RPC did notice the relationship between scalability and statelessness. The NFS RFC explicitly mentions stateless servers, though with reliability as the main concern. Anyway, statelessness is one of the main difference between services and plain old RPC.

In short, no. I don't believe in the revisionist history of SOA being since the dawn of time. Any more than the universe being written in Lisp (or Perl for that matter). Nor is it equivalent to divide and conquer or division of labour.

SOA started as a concept at some point in the nineties. Overlapping with the development of CORBA. It is much harder to pinpoint an actual date or event and there are more than a few claims to the conceptualisation of it.