A job posting I am interested in calls for "full knowledge of orchestration methodologies".
Is there a recognized list of such methodologies? Or is it another name for specific orchestration algorithms or properties like synchronous/asynchronous, transactional, long-running etc.?
orchestration means "An arrangement of events that attempts to achieve a maximum effect" by meaning "full knowledge of orchestration methodologies" they would like to ask whether you know the way to perform such events that produces the maximum result they want.
OR this could be A programming model for the orchestration of Web services
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I know that the question seems odd, but I'll try to explain it as well as I can.
I have a docker-compose file with 4 services: zookeeper, kafka, schema registry and redis. Besides that, I also have 2 SpringBoot microservices which use the dockerized services. The first microservice receives HTTP requests from Postman and then processes those requests before sending them to a topic. The second microservice reads from that topic, processes the messages and sends them to, you've guessed it, another topic.
How would a UML use-case diagram for this situation look like? I have no idea how to start because I've always identified roles first and took it from there. In this case, there are no people actually using it because it's just meant to collect some data and manipulate it.
My professor told me I had to have a use-case diagram, so I suppose it has to be possible to draw it, I'm just confused in how to start.
Also, if you have any recommendations on which diagrams can explain microservices nicely, let me know.
You are already focusing on a technical solution, i.e. how should it work. You have described here in details a system made of several microservices, and using some identified technologies for their implementation.
But the systems have a purpose. They are meant to interact with some actors and help themto achieve some goals. This is what use-cases are about: what's the purpose of the system for which actor. And whether it’s 12 microservices or 1 monolith, does absolutely not influence the use-cases, since these are independent of the inner structure of the system.
Unfortunately, nothing in the narrative tells us what this system is supposed to to nor for whom. This is where you should start.
Finally actors of the UC diagram can be human users or technical systems (i.e. independent systems).
You can use feature in use case diagram called include. Basically, include means a use-case will call other specific use-case. (see https://www.uml-diagrams.org/use-case-diagrams.html for reference). If you have chain of activity on multiple microservices, you can connect them using include like so:
Note that use case diagram doesn't care about technology used to build an app. It doesn't care what's under the include between your services. It was intended as pure abstraction to allow non-developers to understand it.
I would like to model an application architecture and the time-outs between all the application (e.g. between application A and B there is a time-out of 10 seconds and that between all applications). Which modelling language should I best use for this that it is clear? I don't think UML diagrams will do the trick...
Thanks.
It depends on the purpose of your model.
Business oriented process orchestration
For orchestration between several tasks/activities of several applications of a complex process, you could use Business Process Model and Notation (BPMN), which is a standard of the OMG.
There you can model event-based "gateways" to control flow of control or "messages" between activities. An event could be in your case a timer or a error (e.g. time-out errors) depending on the desired emphasis.
Remark: THere are several third party tools that use BPMN models to generate BPEL in order to to make the modelled process orchestration exectutable.
Technical model
If you want to show interaction between applications, but not necessarily modelled as business processes (user perspective), you could also really consider UML:
activity diagrams can present event actions and also timers
eventually, sequence diagrams could present timing constraints and conditions. But intuitively I doubt it's the best choice for your question here.
Christophe's answer is correct. However, you can show time out with basic activity diagrams by using interruptible regions and an interrupt flow like this:
Of course BPMN can do that much better.
Did not find a more suitable SE site, so asking this here.
In BPM, there are more-or-less standard ways of marking activities - like Start (green circle), Stop (red circle), Conditional (yellow diamond). An example I found is here.
Conditional is basically an 'if' in any programming language.
What I could not find any example of is a 'switch'.
I know that one could use multiple Conditionals, but I have to implement a user friendly way, so I'd like to know if there is any standard way of representing such a thing in BPM.
It depends on what you mean by "switch". If you want to switch process flow in one or another way you can use Complex Gateway. A Complex Gateway allows the modeler to specify any arbitrary rules needed to determine how to emit tokens or process arriving tokens.
BPMN Complex Gateways can be used for splitting or merging a complicated process flow scenario. However, it is not recommended practice as there are simpler and more practical inclusive and exclusive gateways. There is always better to use their combination. You can learn more about complex gateways here.
I'm doing some research on the workflow concepts and specifically BPMN standard. And I'm mostly interested in the available software on the subject.
I've already studied software like Activiti and jBPM, both of which are implemented in Java. As great as they are, I'm looking for something else. Even though such software call themselves BPM Engine I would rather name them BPM Engine Servers. They are stand alone servers (with web based GUI) which makes it really hard to embed them in other servers.
Now my question is: Is there a concept as BPM Engine in the manner it only executes the given BPM with the given data, only one step? Without any GUI or direct user interaction (something like a library)? What should I search for? What is it named? Are my expectations valid?
[UPDATE]
I've spent the last hours studying Activiti's user guide. I'm still not sure if I can use it the way I want it to! And I'll be grateful if someone can confirm it.
I'm interested in a console-like application which I can run whenever I like, give it the previously running process (most likely serialized as a string). The engine should construct the process based on the given history.
Once the process is reconstructed, I would like to move it forward one step by telling it what has happened. Then it should inform me of the next tasks to be performed and shutdown.
Finally I'll be storing the updated process after getting it as a string (the engine should serialize it in a way so it can unserialize it later).
I don't want the engine to have its own database or memory storage. I want it to shutdown completely once it's done. This is what I mean by Engine, no user interaction, no storage access.
Can any of the BPM engines perform in such a way?
perhaps I am missing your point, but Activiti is really nothing more than a jar file that can be embedded in any other java application. Certainly in order to run Activiti in any meaningful way you need a backing datastore (database) and one or more process definition, but as you can see from the unit tests that are part of Activiti, the database can be in memory and the process definition can be included in the war. There are many examples of Activiti (and likely jBPM) used as simply an embedded state machine with no exposed UI or user interaction.
My company has implemented a number of such solutions for different organizations.
If I have missed your point, feel free to give me an example of your requirement, I'm sure we have addressed it at one time or another.
You might be interested in Bonita BPM.
This open source BPM solution offers an execution engine that can be used as a standalone.
Just like its competitors, it also offers an optional GUI in the form of a web based application: Bonita Portal.
I think the challenge for what you want to do is that most of the BPM Engines separate the definition of the process from the execution. So for most of them you need someplace that will allow you to store the definition long term (typically a database) and then they track the state of a given instance of that definition for you.
If you wanted a truly stateless BPMN "interpretation" engine, then your serialized data would have to include not only the current state of the process, but he process definition as well. I'm sure this can be done, but I don't think any of the engines have taken this approach as doing so would add complexity to the solution, and solves a problem that not many people seem to be asking about.
Additionally it begs the question "given that we now have a process that knows what task it is on, how does that task actually get executed?" In most of the solutions I've seen the execution of the task takes place in the same server as the engine. In some where the execution is in a different technology, the "executor" doesn't understand the Process much at all except to make a call to signal "okay this thing is done" and the engine handles what happens next. You want to have this data in a serialize data structure of some sort, so the question would arise "If we have this stateless BPMN Engine, would the executor of the task have to update the serialized data to indicate the state change for the task".
There are other requirements of the BPMN specification that I think would make your approach very difficult, such as how to handle items like Intermediate Message Events that are either waiting for a specific time, or a message, before moving the process forward. While all of these are potentially solvable, it certainly would take significant re-engineering of current approaches.
I've encountered the term "multi-agent computing" as of late, and I don't quite get what it is. I've read a book about it, but that didn't answer the fundamental question of what an agent was.
Does someone out there have a pointer to some reference which is clear and concise and answers the question without a load of bullshit/marketing speak? I want to know if this is something I should familiarise myself, or whether it's some crap I can probably ignore, because I honestly can't tell.
In simple terms, multiagent research tries to design system composed of autonomous agents. That is, you have a bunch of robots/people/software-agents around, each of which can take its own actions but can only "see" stuff that is around him, how do get the system to behave as you want?
Example,
Given a bunch of robots with limited sensing capabilities, how do you get them to monitor a field for enemies? to find all the mines in a field?
Given a bunch of people, how do you get them to maximize the happiness of the least happy person? without taking away their freedom.
Given a group of people, how do you set up a meeting time(s) that maximizes their happiness? without revealing their private information?
Some of these questions might appear really easy to solve, but they are not.
Multiagent research mixes techniques from game theory, Economics, artificial intelligence, and sometimes even Biology in order to answer these questions.
If you want more details, I have a free textbook that I am working on called Fundamentals of Multiagent Systems.
A multi-agent system is a concept borrowed from AI. It's almost like a virtual world where you have agents that are able to observe, communicate, and react. To give an example, you might have a memory allocation agent that you have to ask for memory and it decides whether or not to give it to you. Or you might have an agent that monitors a web server and restarts it if it hangs. The main goal behind multiagent systems is to have a more Smalltalk-like communication system between different parts of the system in order to get everything to work together, as opposed to more top-down directives that come from a central program.
"Agents" are another abstraction in software design.
As a crude hierarchy;
Machine code, assembly, machine-independent languages, sub-routines, procedures, abstract data types, objects, and finally agents.
As interconnection and distribution become more important in computing, the need for systems that can co-operate and reach agreements with other systems (with different interests) becomes apparent; this is where agents come in. Acting independently agents represent your best interests in their environment.
Other examples of agents:
Space craft control, to make quick decisions when there's no time for craft-ground crew-craft messaging (eg NASA's Deep Space 1)
Air traffic control (Systems over-riding pilots; this is in place in most commercial flights, and has saved lives)
Multi-agent systems are related to;
Economics
Game theory
Logic
Philosophy
Social sciences
I don't think agents are something you should gloss over. There's 2 million hits on google scholar for "multi agent" and more on CiteSeer; it's a rapidly evolving branch of computer science.
There are several key aspects to multi-agent computing, distribution and independence are among them.
Multi-agents don't have to be on different machines, they could as #Kyle says, be multiple processes on a single chip or machine, but they act without explicit centralised direction. They might act in concert, so they have certain synchronisation rules - doing their jobs separately before coming together to compare results, for example.
Generally though the reasoning behind the segmentation into separate agents is to allow for differing priorities to guide each agent's actions and reactions. Perhaps using an economic model to divide up common resources or because the different functions are physically separated so don't need to interact tightly with each other.
<sweeping generalisation>
Is it something to ignore? Well it's not really anything in particular so it's a little like "can I ignore the concept of quicksort?" If you don't understand what quicksort is then you're not going to fail to be a developer because most of your life will be totally unaffected. If you have more understanding of different architectures and models, you'll have more knowledge to deploy in new and unpredictable places.
<sweeping generalisation>
Ten years ago, 'multi-agent systems' (MAS) was one of those phrases that appeared everywhere in the academic literature. These days it is less prevalent, but some of the ideas it represents are really useful in some places. But totally unnecessary in others. So I hope that's clear ;)
It is difficult to say what multi-agent computing is, because the definition of an agent is usually very soft surrounded by markting terms etc. I'll try to explain what is it and where it could be used based on the research of manufacturing systems, which is the area, I am familiar with.
One of the "unsolved" problems of modern manufacturing is scheduling. When the definition of the problem is static, an optimal solution can be found, but in reality, people don't come to work, manufacturing resources fail, computers fail etc. The demand is changing all the time, different products are required (i.e. mass customization of the product - one produced car has air conditioning, the next one doesn't, ...). This all leads to the conclusions that a) manufacturing is very complex, b) static approaches, like scheduling in advance for a week, don't work. So the idea is this: why wouldn't we have intelligent programs representing parts of the systems, working the way out of this mess on their own? These programs are called agents. They should communicate and negotiate amongst themselves and make sure the tasks are done in due time. By using agents we want to lower the complexity of the control system, make it more manageable, enable better human - machine interaction, make it more robust and less error prone and very importantly: make the control system decentralized.
In short: agents are just a concept, but they are a concept everyone can intuitively understand. Code still needs to be written, but it is written in a different way, one abstraction higher than OOP.
There was a time when it was hard to find good material on software agents, primarily because of the perception of marketing potential. The bloom on that rose has diminished so the signal to noise ratio on the Internet has improved vis-a-vie software agents.
Here is a good introduction to software agents on this blog post of an open source project for software agents. The term multi-agent systems just means a system where multiple software agents run and communicate and delegate sub tasks to each other.
According to Jennings and Wooldridge who are 2 of the top Mulit-agent researchers an agent is an object that is reactive to its environment, proactive and social. That is an agent is a piece of software that can react to its environment in real time in a way that is suitable to its own objeective. It is proactive, which means that it doesnt just always wait to be asked to perform a task, if it sees a chance to do something that it feels would be beneficial to its objectives it does it. And that it is social, ie that it can communicate with other Agents, doesnt nessecaily ever have to do any of these things in meeting its own objectives but it should be able to to do these if the situation arose. And thus a multi-agent system is just a collection of these in a distrubuted system that can all communicate and try to perform their own personal goals hat normally lead to an overall achievement of the system goal.
You can find a concentration of white papers concerning agents here.