Background: an international company with a federation model is transforming into Microservices due to chronic Monolithic pain. Autonomous teams with quick deployment is highly desirable. In spite of theory, services are indeed dependent on each other for higher functionality, but are autonomous (independently developed and deployed). Since this is a federation model and decentralized control, we cannot impose strict rules - just like the UN. Without a governance platform that will manage dependencies else due to the multiple versions in production in different countries, we foresee uncontrollable chaos.
Let's call set of Microservices that needs to collaborate a "Compatibility Set". A service can be deployed but may not satisfy the higher functionality in its Compatibility Set. For example MicroService A-4.3 is fully autonomous, deployed and working perfectly. However to satisfy BusinessFunctionality 8.6 it must work together with MicroService B-5.4 and MicroService C-2.9. Together (A-4.3 , B-5.4 and C-2.9) they form a "Compatibility Set"
There are two approaches to this dilemma. Microservice in real life where the rubber hits the road and the learning from experience begins...
Approach 1) Governance Platform
Rationale: Federal model in an International company in 100+ countries. Which means Central IT can lay down the model but individual countries can choose their own destiny - and they frequently do. It frequently devolves to chaos and the Central IT team is on the hook. DDD is the solution for an ideal world where version inconsistencies do not derail functionality like releasing services which do not fit into the Compatibility set, individually blameless but together they fall apart or result in flawed or inconsistent functionality.
There is no homogeneity, there isn't even standardization of terminology
Developers are mixed skill, many junior, and many learning reactive programming and cloud native technologies
Bounded Context heavily depends on Shared Vocabulary and it can get subtle, but this is impossible to enforce and naive to assume in an International, mixed skill, fragmented scenario with multiple versions running
Standardization on a Single Business Model is not realistic in such a heterogeneous system (but ideal)
How what is Central IT to do when they're held responsible for this Chaos?
Enforce a Governance Platform
Create a Microservices governance system or framework to enforce dependency management. It verifies and enforces at design and run time dependencies on a particular Microservice through a manifest and performs some checks and balances to verify the service implementations being offered - the "Compatibility Set".
Approach 2) Domain Driven Design (DDD)
DDD is about modelling domains that are constantly evolving, where domain experts (typically a business stakeholder, or perhaps an analyst) will work alongside developers to design the system. Within each domain, a ubiquitous language is formed, such that within that context, the same word always means the same thing. An important thing to realise is that in one part of your system, “Order” might mean one thing, it might mean for example a list of products. In another part of your system, “Order” might mean something else, it might mean a financial transaction that happened. This is where the model you describe can fall down, if my service needs to get a list of orders, perhaps there is a capability out there that supplies a list of orders, but which orders are they? The list of products or the financial transaction? Trying to coordinate as many developers as you have to all use the same language here is an impossible task that is doomed to fail.
In DDD, rather than trying to manage this at a system level and force every service to use the same definition of Order, DDD embraces the inherent complexity in coordinating very large deployments with huge numbers of developers involved, and allows each team to work independently, coordinating with other teams as needed, not through some centralised dependency management system. The term used in DDD is bounded contexts, where in one context, Order means one thing, and in another bounded context, Order can mean another thing. These contexts can function truly autonomously – you describe your services as being autonomous, but if they have to match their definition of order with the entire system by registering and supplied dependencies to a central registry, then really they are tightly coupled to the rest of the system and what it considers an order to be – you end up with all the painful coupling of a monolith, with all the pain of building a distributed system, and you won’t realise many of the benefits of microservices if you try to take this approach.
So a DDD based approach doesn’t ever try to take a heavy handed approach of enforcing dependencies or capabilities at the system level, rather, it allows individual teams to work without needing central coordination, if Service A needs to interact with Service B, then the team who manages Service A will work with the team that manages service B, they can build an interface between their bounded contexts, and come to an agreement on language for that interface. It is up to these teams to manage their dependencies with each other, at the system level things can remain quite opaque / unenforced.
Too often we see people implement “Microservices” but end up with a system that is just as, if not more inflexible, and often more fragile, than a monolith. Also called a "Minilith" or "Monolith 2.0" Microservices require a complete rethink of architecture and software development processes, and require not just allowing services to be autonomous and independently managed, but also for teams to be independent, not centrally managed. Centralising the management of dependencies and capabilities in a system is likely to be an inhibitor to successfully building a microservice based system.
Intelligent and Pragmatic comments invited...
Approach 1 (Governance) is pragmatic and tactical and intended to solve very real challenges. Question is - will it undermine the long term strategic DDD model of the Enterprise?
Approach 2 (DDD) is ideal and aspirational but doesn't address the very real challenges that we have to deal with right now.
Opinions? Thought? Comments?
I've seen multi-national companies try to cooperate on a project (or be controlled from a central IT team) and it's a nightmare. This response is highly subjective to what I've personally read and seen, so it's just my opinion, it's probably not everyone's opinion. Generally broad questions aren't encouraged on Stack Overflow as they attract highly opinionated answers.
I'd say DDD probably isn't the answer. You'd need a large number of a developers to buy into the DDD idea. If you don't have that buy-in then (unless you have a team of exceptionally self-motivated people) you'll see the developers try to build the new system on-top of the existing database.
I'd also argue that microservices aren't the answer. Companies that have used microservices to their advantage are essentially using them to compartmentalise their code into small, stacks of individually running services/apps that each do a single job. These microservices (from the success stories I've seen) tend to be loosely coupled. I imagine that if you have a large number of services that are highly coupled, then you've still got the spaghetti aspects of a monolith, but one that's spread out over a network.
It sounds like you just need a well architected system, designed to your specific needs. I agree that using DDD would be great, but is it a realistic goal across a multi-national project?
I also dealt with the problem described in the question. And I came up with an approach in which I use API-definitions like OpenAPI-definitions to check compatibility between two services. The API-definitions must be attached as metadata to each service and therefore it is possible to do the check at run and design time. Important is that the API-definitions are part of the metadata as well when the API is offered and when the API is used. With tools like Swagger-Diff or OpenAPI-Diff it is possible to do the compatibility-check automated.
Related
The problem I'm facing is the design of an integration platform.
The company has different tools used for selling online financial services and wants to unify the selling process by creating a common integration platform.
Existing tools range from simply designing a tailor-made offer, to managing all the phases of listing to selling and supporting. The integration platform should orchestrate all the tools.
So I do approach this problem from a DDD point of view?
Domain: selling online services
subdomains: service catalog, request offers, sending offers, buying service, support customer.
bounded context? maybe integration with other company systems like identities and invoices?
My trouble with this is that some existing applications encompass several subdomains, others don't. Also, some applications working in the same subdomain have completely different languages, for example, service vs product, vs project...
How does an integration platform fit in this picture and how would you approach it from a DDD point of view? (or maybe it's a completely wrong approach and should I leave DDD inside each tool and treat them as bounded context?)
I recommend extracting the common bits of meaning (ignoring their names) from the various applications into common domains/bounded contexts. Each bounded context has anti-corruption layers that essentially adapt the language used in one or more existing applications to the one used in the common domain (and vice versa). Then you can cut over the existing applications piece-by-piece to use the respective ACLs to take advantage of the common domain implementation.
Eventually, you might even be able to dispense with the ACLs, as the language becomes more ubiquitous, but it's also perfectly okay to keep them around forever: the ACLs introduce some indirection (and possibly complexity, e.g. if they're deployed as their own microservices) but that's the price you pay for limiting coupling to the ACL.
(It's not clear from the question how experienced you are with DDD).
I'm currently learning about Microservices because in the company where I work, we will split down our giant monolith into microservices.
We have a lot of business logic in our application, but this rules basically validate data from many different domains and act accordingly the status of this data.
Our domain has it's own data, of course, but I even dare to say we depend something like 60 ~ 70% of data from different domains, which makes our domain kind of an aggregator.
I created a little diagram to illustrate it:
So like I said before, my domain (Domain A) has a lot of business logic to validate data and status from all those different domains. And then after this validation, take the appropriate actions and save the result of it in the DB.
I feel like I hit a dead end, cause I have read a few articles how to break down a monolith, but I haven't got any good example where it explains this situation.
So I ask you guys, do you have any suggestions to tell me? :)
Thanks!
In DDD speak a bounded context approximates a microservice. The different domains in your diagram are probably going to be bounded contexts.
You most certainly do not want concepts from various BCs polluting each other as you are going to end up with quite a mess.
There is one place, however, where you may run into this and that is on integration/orchestration. Here you should approach this concern almost as a separate BC that relates to the orchestration or integration.
For instance, let's assume that you have an Assets domain and an Accounting domain. The two should know nothing about each other. However, when you decommission an asset (say some huge machine that grinds down rocks into stones) you perhaps need to have the accounting domain register some write-off value if the asset has not reached the end of its useful life. In this layer you would integrate the various bits of your process and manage the state using a process manager. Although the process manager, and related state, may belong to the Assets BC the AssetsOrchestration BC may make use of objects from both the Assets as well as the Accounting BCs. Typically you would attempt to limit that interaction to, say, messages using some messaging infrastructure but YMMV.
A good starting point may be Sam Newman's Microservice Decomposition Patterns.
About 18 minutes into the talk, Newman offers this pattern:
Within your monolith, identify the coarse modules of functionality.
Draw the dependency graph
OK, your dependency graph has cycles in it. That's no good, you want an acyclic graph. So iterate on the graph until you are able to eliminate the cycles. DO NOT PASS GO until you have this done
Identify candidate modules that have no inbound dependencies - you want the bits that nothing else depends on.
Pick one, and see if you can redesign your system to allow you to deploy that module independently of the monolith.
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I am a web developer, I want to become software architect, and I learn everyday about it, but when I am learning software architecture I see TOGAF framework for enterprise architecture, I want to get solid understand in an enterprise architecture.
Overview
Enterprise architecture focuses on the future state solution for : Current business problem , business strategy , business process improvement (BPI), business process re-engineering and business adventures. If you ask one enterprise architect what they are working on, most likely you are going to find out that they are working on one of these areas, unless they have a more specialized domain, which we cover later in this article.
“The What”
Enterprise Architecture does not prescribe the “how” only the what,
Deliverables
Depending on your company solution lifecycle standards and templates, your deliverable may be called “solution architecture”, “Enterprise Architecture blueprint” or some other name.
Architecture layers
It is a good practice to include in your deliverable minimum six architecture layers:
Security: End to end view of your solution from security perspective, this captures authentication and access management, data in transit and at rest protection.
Application: A view of your solution from the application perspective, includes domain specific programming language, and application design patterns and decisions for your font end, back-end and middle tier.
Infrastructure: This layer shows a view of your running platform, it may include cloud, containerization and virtualization.
Information: This captures your entire information lifecycle management from data modeling to acquisition, classification, and retirement.
Network: This architecture layer depicts the network end points and their paths.
Integration: This layer shows your data transportation and systems conversations, for example it shows your separations of data transportation from orchestration.
While these layers are not the only layers hat you can add to your architecture, you can add more as needed for example “business continuity” and “devops”, but all depends on the type of your organization and objectives.
The Enterprise Architect role
Being an Enterprise Architect (EA) entails command in multiple domains , however most of us in this industry started our careers in one domain such as development, networking, DBA, etc, an architect usually have expertise in at least one of the following and experience in the rest.
Expertise in one programming language (expert level means very familiar with the language and design patterns specific to the language).
Expertise in one database vendor ( Oracle, MSSql, DB2) expert level means - - Expertise in SQL , SQL:2016 being the latest standard in addition to server side language (PLSQL, TSQL)
Experience in networking basic concepts of networking and knowledge of new trends such as software defined networks (SDN).
Experience in integration patterns
Experience in infrastructure such as cloud , virtualization and containerization
Experience in information security: Identity and access management , Data in transit and data at rest protection.
In addition basic knowledge in : Data modeling, data warehousing, big data, Web UI frameworks, major cloud providers, compliance (ie: PCI, HIPPA), IPV4, IPV6, SOA.
And also helps if you have your own vision of the future landscape (ie: server-less , self-rendering services )
Architecture frameworks
There are multiple frameworks that depending on the situation may fit in your deliverables, these frameworks try to address the common architecture patterns in a prescriptive way.
TOGAF
Zachman
DoDAF
To answer your question " what s the difference between system architecture, application, software architecture":
Application architecture is one of the layers in your architecture.
System architecture, software architecture, solution architecture can be used interchangeably. Just don't lose your the big picture .
Some of the inputs for the architecture are
business strategy.
use cases
business cases.
Business continuity strategy
Compliance
Some of the outputs are
High level designs
A vertical partition) of your architecture layers.
Software specifications
A prescriptive and technology oriented specifications of your solution.
I have presented on Enterprise Architecture a few times over the past couple of years. One of the quotes (from myself) that I use in my talks is: "Just because I am an Enterprise Architect, that does not mean that I am an Enterprise Architect". That might seem like a strange quote but it's basically just a fun way to say that enterprise architecture can mean different things to different organizations and people.
Enterprise architects tend to work across a broad domain of concerns, occasionally focusing on specific aspects of a specific technology and/or business process. Some organizations (they tend to be the ones with a more mature EA practice) will have architects that work across all domains within the organization (or, enterprise - hence enterprise architect). Some organizations will have specific types of architects (e.g. applications architect, solutions architect, data architect, network/systems architect, business architect, etc.) that focus on a particular area. Having various types of architects within an organization is one way to "ease" yourself into the architecture space.
For example, the organization I work for has the role, Lead Developer. Each development team has a lead developer and they essentially act as applications architects (even if that is not their specific title). For someone new to that role, they focus on learning the business domain their team is typically responsible for. They also provide the overall architectural vision and design for the apps their team produces. And, they also work closely with the enterprise architects to ensure they are working within the parameters of the organization as a whole (i.e. not reinventing the wheel or making use of a technology or approach that does not fit within the enterprise architecture as a whole).
Starting out as a lead developer is one way to get your foot in the door, so to speak. There are other ways. For example, if you're interested in data architecture, then joining a BI team would be a great way to learn more about data architecture at scale. Joining a network team would go a long way toward gaining knowledge that could be applied as a network/systems architect.
You mention TOGAF in your question above but there are many architectural frameworks out there (TOGAF, Zachman, DoDAF, etc.). Depending upon your specific situation, a "canned" framework might make sense for your organization and it might not. However, becoming familiar with some of the available frameworks will give you insights into some of the common challenges faced by enterprise architects. In the end, however, you will want to do what is right for your organization. You might take bits and pieces from multiple frameworks and wrap them all up into your own framework. As with many challenges, do what works for you.
Along with everything else, keep in mind that enterprise architects tend to think strategically and keep a focus on the future. That does not mean that they do not think tactically or are not concerned with the "here and now". They just tend to have strengths when it comes to strategy and vision.
While this is a bit of a wordy answer, the reality is that nothing beats experience. If you want to become an enterprise architect then you should try to apply architectural practices to your everyday tasks. The more you work and act like an enterprise architect the more ready you will be when an opportunity presents itself.
Hope this helps!
If you want to be a software architect - aka Application Architect, then TOGAF is useful to know, but not necessary for you. Enterprise architects deal with things that impact the entire organisation, particularly things like Strategy & Planning. Organisational modelling, etc.
They can be sometimes involved as a governance role to ensure alignment with organisational design standards, or security standards. They can also sometimes be involved in setting organisational policy.
Either way - too many people assuming taking the "most senior looking" title will get them the best pay and the best life - this is not always true and an EA role is very very different to a software architect - even though they are both "Architects"
Now getting a solid understanding of Enterprise Archtiecture will be a challenge - because 1. its kind of undefined right now - or more accurately - there is around 460+ different models of what an Enterprise Architecture is - TOGAF only being one of them. 2. Most EAs like to get completely OCD around model definitions, and each one has a different OCD point of view exactly what they are - I should know, I'm one of them :)
One of the best general models I have found is DoDAF, but it sure isn't light bedtime reading. Wikipedia has a reasonably light definition though and it might be worth starting there if you haven't already
Enterprise Architecture (EA) entails the whole organization and possibly beyond. It includes Business Architecture, Information Architecture, Technology Architecture & Application Architecture. EA is strategic and thus it is "What" needs to be done.
Can somebody please explain (in succinct terms) what exactly is domain driven design? I see the term quite a lot but really don't understand what it is or what it looks like. How does it differ from non-domain driven design?
Also, can somebody explain what a Domain Object is? How does domain differ from normal objects?
EDIT:
As this seem to be a top result on Google and my answer below is not, please refer to this much better answer:
https://stackoverflow.com/a/1222488/1240557
OLD ANSWER (not so complete :))
In order to create good software, you have to know what that software
is all about. You cannot create a banking software system unless you
have a good understanding of what banking is all about, one must
understand the domain of banking.
From: Domain Driven Design by Eric Evans.
This book does a pretty good job of describing DDD.
Register to download a summary of the book.
Domain Driven Design is a methodology and process prescription for the development of complex systems whose focus is mapping activities, tasks, events, and data within a problem domain into the technology artifacts of a solution domain.
The emphasis of Domain Driven Design is to understand the problem domain in order to create an abstract model of the problem domain which can then be implemented in a particular set of technologies. Domain Driven Design as a methodology provides guidelines for how this model development and technology development can result in a system that meets the needs of the people using it while also being robust in the face of change in the problem domain.
The process side of Domain Driven Design involves the collaboration between domain experts, people who know the problem domain, and the design/architecture experts, people who know the solution domain. The idea is to have a shared model with shared language so that as people from these two different domains with their two different perspectives discuss the solution they are actually discussing a shared knowledge base with shared concepts.
The lack of a shared problem domain understanding between the people who need a particular system and the people who are designing and implementing the system seems to be a core impediment to successful projects. Domain Driven Design is a methodology to address this impediment.
It is more than having an object model. The focus is really about the shared communication and improving collaboration so that the actual needs within the problem domain can be discovered and an appropriate solution created to meet those needs.
Domain-Driven Design: The Good and The Challenging provides a brief overview with this comment:
DDD helps discover the top-level architecture and inform about the
mechanics and dynamics of the domain that the software needs to
replicate. Concretely, it means that a well done DDD analysis
minimizes misunderstandings between domain experts and software
architects, and it reduces the subsequent number of expensive requests
for change. By splitting the domain complexity in smaller contexts,
DDD avoids forcing project architects to design a bloated object
model, which is where a lot of time is lost in working out
implementation details — in part because the number of entities to
deal with often grows beyond the size of conference-room white boards.
Also see this article Domain Driven Design for Services Architecture which provides a short example. The article provides the following thumbnail description of Domain Driven Design.
Domain Driven Design advocates modeling based on the reality of
business as relevant to our use cases. As it is now getting older and
hype level decreasing, many of us forget that the DDD approach really
helps in understanding the problem at hand and design software towards
the common understanding of the solution. When building applications,
DDD talks about problems as domains and subdomains. It describes
independent steps/areas of problems as bounded contexts, emphasizes a
common language to talk about these problems, and adds many technical
concepts, like entities, value objects and aggregate root rules to
support the implementation.
Martin Fowler has written a number of articles in which Domain Driven Design as a methodology is mentioned. For instance this article, BoundedContext, provides an overview of the bounded context concept from Domain Driven Development.
In those younger days we were advised to build a unified model of the
entire business, but DDD recognizes that we've learned that "total
unification of the domain model for a large system will not be
feasible or cost-effective" 1. So instead DDD divides up a large
system into Bounded Contexts, each of which can have a unified model -
essentially a way of structuring MultipleCanonicalModels.
You CAN ONLY understand Domain driven design by first comprehending what the following are:
What is a domain?
The field for which a system is built. Airport management, insurance sales, coffee shops, orbital flight, you name it.
It's not unusual for an application to span several different domains. For example, an online retail system might be working in the domains of shipping (picking appropriate ways to deliver, depending on items and destination), pricing (including promotions and user-specific pricing by, say, location), and recommendations (calculating related products by purchase history).
What is a model?
"A useful approximation to the problem at hand." -- Gerry Sussman
An Employee class is not a real employee. It models a real employee. We know that the model does not capture everything about real employees, and that's not the point of it. It's only meant to capture what we are interested in for the current context.
Different domains may be interested in different ways to model the same thing. For example, the salary department and the human resources department may model employees in different ways.
What is a domain model?
A model for a domain.
What is Domain-Driven Design (DDD)?
It is a development approach that deeply values the domain model and connects it to the implementation. DDD was coined and initially developed by Eric Evans.
Culled from here
Here is another good article that you may check out on Domain Driven Design. if your application is anything serious than college assignment. The basic premise is structure everything around your entities and have a strong domain model. Differentiate between services that provide infrastructure related things (like sending email, persisting data) and services that actually do things that are your core business requirments.
Hope that helps.
As in TDD & BDD you/ team focus the most on test and behavior of the system than code implementation.
Similar way when system analyst, product owner, development team and ofcourse the code - entities/ classes, variables, functions, user interfaces processes communicate using the same language, its called Domain Driven Design
DDD is a thought process. When modeling a design of software you need to keep business domain/process in the center of attention rather than data structures, data flows, technology, internal and external dependencies.
There are many approaches to model systerm using DDD
event sourcing (using events as a single source of truth)
relational databases
graph databases
using functional languages
Domain object:
In very naive words, an object which
has name based on business process/flow
has complete control on its internal state i.e exposes methods to manipulate state.
always fulfill all business invariants/business rules in context of its use.
follows single responsibility principle
DDD(domain driven design) is a useful concept for analyse of requirements of a project and handling the complexity of these requirements.Before that people were analysing these requirements with considering the relationships between classes and tables and in fact their design were based on database tables relationships it is not old but it has some problems:
In big projects with complex requirements it is not useful although this is a great way of design for small projects.
when you are dealing with none technical persons that they don,t have technical concept, this conflict may cause some huge problems in our project.
So DDD handle the first problem with considering the main project as a Domain and splitting each part of this project to small pieces which we are famous to Bounded Context and each of them do not have any influence on other pieces.
And the second problem has been solved with a ubiquitous language which is a common language between technical team members and Product owners which are not technical but have enough knowledge about their requirements
Generally the simple definition for Domain is the main project that makes money for the owners and other teams.
I do not want to repeat others' answers, so, in short I explain some common misunderstanding
Practical resource: PATTERNS, PRINCIPLES, AND PRACTICES OF DOMAIN-DRIVEN DESIGN by Scott Millett
It is a methodology for complicated business systems. It takes all the technical matters out when communicating with business experts
It provides an extensive understanding of (simplified and distilled model of) business across the whole dev team.
it keeps business model in sync with code model by using ubiquitous language (the language understood by the whole dev team, business experts, business analysts, ...), which is used for communication within the dev team or dev with other teams
It has nothing to do with Project Management. Although it can be perfectly used in project management methods like Agile.
You should avoid using it all across your project
DDD stresses the need to focus the most effort on the core subdomain. The core subdomain is the
area of your product that will be the difference between it being a success and it being a failure. It’s
the product’s unique selling point, the reason it is being built rather than bought.
Basically, it is because it takes too much time and effort. So, it is suggested to break down the whole domain into subdomain and just apply it in those with high business value. (ex not in generic subdomain like email, ...)
It is not object oriented programming. It is mostly problem solving approach and (sometimes) you do not need to use OO patterns (such as Gang of Four) in your domain models. Simply because it can not be understood by Business Experts (they do not know much about Factory, Decorator, ...). There are even some patterns in DDD (such as The Transaction Script, Table Module) which are not 100% in line with OO concepts.
I believe the following pdf will give you the bigger picture. Domain Driven Design by Eric Evans
NOTE: Think of a project you can work on, apply the little things you understood and see best practices. It will help you to grow your ability to the micro service architecture design approach too.
Get an organization wide understanding of the problem domain by
developing a ubiquitous language (a common mental model) per sub-problem-domain.
Use that language as close as possible in solution domains (code).
Only then choose technologies.
Don't be technology driven but problem domain or business driven.
I'm interested in the history of distributed, collaborative, 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.