I'm working on a project that uses an extremely complex BPMN file, so I've been tasked with seeing if splitting it into multiple BPMNs can be done i.e. have it go from one BPMN file into another. We are using Eclipse's BPMN2 Modeler, are there any ways of doing this outside of implementing a Sub-Process? And is there a way for it to happen as a user carries out tasks rather than right at the start, for instance when the user reaches a certain point in the sequence it jumps to another BPMN, otherwise it does not?
You could use message events to signal to different lanes/flows of your original BPMN.
This would enable you to split the flow into sub-BPMN diagrams which can accept message events to start the sub-flow, and emit message events when they're complete to continue the wider process.
Subprocesses is the best way to split chunks of processes into separate units. Based on your question: "for instance when the user reaches a certain point in the sequence it jumps to another BPMN" that is when you place a sub process activity.
I wonder why you are discarding that approach.
Related
I am using Anylogic for a simulation-modeling class, and I am not anylogic or coding smart. My last and only coding class was MatLab based about 16 yrs ago. I have a few questions about how to implement modeling concepts in a discrete model with anylogic.
How can I add/inject agents directly into a queue downstream from a source? I have tried adding an additional source to use the “Calls of inject() function,” but I am not sure how to implement it after selecting it ( example: what do I do after selecting the Calls of inject() function). I have the new source feeding directly into the queue where I want the inject.
How can I set the release of an agent to a defined schedule instead of a rate? Currently, I have my working model set to interarrival time. But I would like to set the agent release to a defined schedule. (example: agent-1 released at 120 seconds, agent-2 released at 150 seconds, agent-3 released at 270 seconds)
Any help would be greatly appreciated, especially if it can be written in a “explain to me like I am 5yrs old” format.
Question 1:
If you have a source connected directly to a queue, then when you call source.inject() an agent will be created at the source block and go to the queue. If you have 1 source with multiple possible destinations, then you will have to use select output blocks and some criteria to go from the source to the desired queue.
Since you mentioned not being a strong programmer, this probably wouldn't be for you, but I often find myself creating agents via add_population and then just adding them to an ArrayList until I am ready to pull them into the DES flow. Really, there are near infinite ways to control agent flow within AnyLogic.
Question 2:
Option a: Arrivals by "Arrival Table in Database" You can link an AnyLogic database table to Excel, and then the source block will just have an agent arrive based on that table.
Option b: Arrival Schedule - you could set this up manually within the development environment or load your schedule from a database. I prefer option a over option b given your brief description.
Option c: Read in data to variable and then write code to release based on next arrival time. 1,000s of ways to do this, but one example could be a list of doubles (your arrival times), set an event to delay until next arrival, call inject function, remove that arrival from the list. I think option a would be best for you, but given that AnyLogic allows you to add java code, there are no limits to how sophisticated you could make your arrival logic.
For 2) You could also use an event or a dynamic event. The action could be source.inject(1); and you can schedule them to your preferences with variables. Just be vigilant that you re-start the events if necessary.
There is a demo-model from AnyLogic for dynamic events.
In the example above I present an example anylogic process flow, excuse me for the link as I'm not allowed to upload pictures yet.
In this flow, is it possible to stop the source from sourcing if the rack system is full or filled to a certain level? (under the assumption that both rack picking and storing is done in that rack system.)
Sure, you can always switch a source off. It depnds on how you defined the arrivals in the source, but for a "Rate" and "Interarrival Time" source, you can use:
mySource.set_rate(0);
All you need to do is to call this in the correct point in your model, i.e. when the rack system is full. To do that, you might need to write a function isFull that loops through all its rows, positions and levels and tests myRackSystem.isFree(row, position, level). If everything is full, you stop the source from creating more stuff.
I have a very complicated job process and it's not 100% clear to me where to handle what.
I don't want to have code, it just the question who is responsible for what.
Given is the following:
There is a root directory "C:\server"
Inside are two directories "ftp" and "backup"
Imagine the following process:
An external customer sends a file into the ftp directory.
An importer application get's the file and now the fun starts.
A job aggregate have to be created for this file.
The command "CreateJob(string file)" is fired.
?. The file have to be moved from ftp to backup. Inside the CommandHandler or inside the Aggregate or on JobCreated event?
StartJob(Guid jobId) get's called. A third folder have to be created "in-progress", File have to be copied from backup to in-progress. Who does it?
So it's unclear for me where Filesystem things have to be handled if the Aggregate can not work correctly without the correct filesystem.
Because my first approach was to do that inside an Infrastructure layer/lib which listen to the events from the job layer. But it seems not 100% correct?!
And top of this, what is with replaying?
You can't replay things/files that were moved, you have to somehow simulate that a customer sends the file to the ftp folder...
Thankful for answers
The file have to be moved from ftp to backup. Inside the CommandHandler or inside the Aggregate or on JobCreated event?
In situations like this, I move the file to the destination folder in the Application service that sends the command to the Aggregate (or that calls a command-like method on the Aggregate, it's the same) before the command is sent to the Aggregate. In this way, if there are some problems with the file-system (not enough permissions or space is not available etc) the command is not sent. These kind of problems should not reach our Aggregate. We most protect it from the infrastructure. In fact we should keep the Aggregate isolated from anything else; it must contain only pure business logic that is used to decide what events get generated.
Because my first approach was to do that inside an Infrastructure layer/lib which listen to the events from the job layer. But it seems not 100% correct?!
Indeed, this seems like over engineering to me. You must KISS.
StartJob(Guid jobId) get's called. A third folder have to be created "in-progress", File have to be copied from backup to in-progress. Who does it?
Whoever's calling the StartJob could do the moving, before the StartJob gets called. Again, keep the Aggregate pure. In this case it depends on your framework/domain details.
And top of this, what is with replaying? You can't replay things/files that where moved, you have to somehow simulate that a customer sends the file to the ftp folder...
The events are loaded from the event store and replayed in two situations:
Before every command gets sent to the Aggregate, the Aggregate Repository loads all the events from the event store then it applies every one of them to the Aggregate, probably calling some applyThisEvent(TheEvent) method on the Aggregate. So, this methods should be with no side effects (pure) otherwise you change the outside world again and again at every command execution and you don't want that.
The read-models (the projections, the query-models) that present data to the user listen to those events and update the database tables that hold the data that the users see. The events are sent to those read-models after they are generated and every time the read-models are being recreated. When you invent a new read-model, you must pass it all the events that were previous generated by the aggregates in order to build the correct/complete state on them. If your read-model's event listeners have side effects what do you think happens when you replay those long past events? The outside world is modified again and again and you don't want that! The read-models only interpret the events, they don't generate other events and they don't change the outside world.
There is a special third case when events reach another type of model, a Saga. A Saga must receive an event only once! This is the case that you thought to use in Because my first approach was to do that inside an Infrastructure layer/lib which listen to the events from the job layer. You could do this in your case but is not KISS.
I have a very complicated job process and it's not 100% clear to me where to handle what. I don't want to have code, it just the question who is responsible for what.
The usual answer is that the domain model -- aka the "aggregate" makes decisions, and saves them. Observing those decisions, some event handler induces side effects.
And top of this, what is with replaying? You can't replay things/files that where moved, you have to somehow simulate that a customer sends the file to the ftp folder...
You replay the events to the aggregate, so that it is restored to the state where it made the last decision. That's a separate concern from replaying the side effects -- which is part of the motivation for handling the side effects elsewhere.
Where possible, of course, you prefer to have the side effects be idempotent, so that a duplicated message doesn't create a problem. But notice that from the point of view of the model, it doesn't actually matter whether the side effect succeeds or not.
Suppose I have an aggregate containing some data and when it reaches a certain state, I'd like to take all that state and pass it to some outside service. For argument and simplicity's sake, lets just say it is an aggregate that has a list and when all items in that list are checked off, I'd like to send the entire state to some outside service. Now when I'm handling the command for checking off the last item in the list, I'll know that I'm at the end but it doesn't seem correct to send it to the outside system from the processing of the command. So given this scenario what is the recommended approach if the outside system requires all of the state of the aggregate. Should the outside system build its own copy of the data based on the aggregate events or is there some better approach?
Should the outside system build its own copy of the data based on the aggregate events.
Probably not -- it's almost never a good idea to share the responsibility of rehydrating an aggregate from its history. The service that owns the object should be responsible for rehydration.
First key idea to understand is when in the flow the call to the outside service should happen.
First, the domain model processes the command arguments, computing the update to the event history, including the ChecklistCompleted event.
The application takes that history, and saves it to the book of record
The transaction completes successfully.
At this point, the application knows that the operation was successful, but the caller doesn't. So the usual answer is to be thinking of an asynchronous operation that will do the rest of the work.
Possibility one: the application takes the history that it just saved, and uses that history to create schedule a task to rehydrate a read-only copy of the aggregate state, and then send that state to the external service.
Possibility two: you ditch the copy of the history that you have now, and fire off an asynchronous task that has enough information to load its own copy of the history from the book of record.
There are at least three ways that you might do this. First, you could have the command schedule the task as before.
Second, you could have a event handler listening for ChecklistCompleted events in the book of record, and have that handler schedule the task.
Third, you could read the ChecklistCompleted event from the book of record, and publish a representation of that event to a shared bus, and let the handler in the external service call you back for a copy of the state.
I was under the impression that one bounded context should not reach out to get state from another bounded context but rather keep local copies of the data it needed.
From my experience, the key idea is that the services shouldn't block each other -- or more specifically, a call to service B should not block when service A is unavailable. Responding to events is fundamentally non blocking; does it really matter that we respond to an asynchronously delivered event by making an asynchronous blocking call?
What this buys you, however, is independent evolution of the two services - A broadcasts an event, B reacts to the event by calling A and asking for a representation of the aggregate that B understands, A -- being backwards compatible -- delivers the requested representation.
Compare this with requiring a new release of B every time the rehydration logic in A changes.
Udi Dahan raised a challenging idea - the notion that each piece of data belongs to a singe technical authority. "Raw business data" should not be replicated between services.
A service is the technical authority for a specific business capability.
Any piece of data or rule must be owned by only one service.
So in Udi's approach, you'd start to investigate why B has any responsibility for data owned by A, and from there determine how to align that responsibility and the data into a single service. (Part of the trick: the physical view of a service can span process boundaries; in other words, a process may be composed from components that belong to more than one service).
Jeppe Cramon series on microservices is nicely sourced, and touches on many of the points above.
You should never externalise your state. Reporting on that state is a function of the read side, as it produces reports and you'll need that data to call the service. The structure of your state is plastic, and you shouldn't have an external service that relies up that structure otherwise you'll have to update both in lockstep which is a bad thing.
There is a blog that puts forward a strong argument that the process manager is the correct place to put this type of feature (calling an external service), because that's the appropriate place for orchestrating events.
My team is new to developing these things and I came into a project that is defining an over-arching workflow using separate processes that are all defined under the same project. So it appears that right now the processes defined are all discrete units, and the plan was to connect these units together using inputs and outputs.
Based on the documentation it looks like the best-practicey way of doing this would be to define the entire, over-arching workflow using sub-process tasks.
So I wonder:
Is the implementation we've started workable?
or
Should I only have one process unit per one workflow, which defines sub-processes if the workflow is too complicated and has discrete parts?
It's fine to separate out certain parts of the process into its own process, and then call those from some sort of parent process. The task you should use in the parent process is called reusable sub-process, or call activity. It's absolutely fine to have multiple processes in the same project.