This question is related to diagraming a software process. As an electrical engineer, much of the software I do is for embedded micro-controllers. In school, we learned to illustrate our algorithm using a flowchart. However, nowadays, many of my embedded projects are heavily interrupt-driven where the main process runs some basic algorithm a variety of interrupt sources provide its stimulus. So, my question is, what are some diagramming techniques that I can use to illustrate my process such that future developers can understand what I am doing easily and get involved in development?
Here are some key features that I am looking for:
Shows data structures and how data is passed between processes & interrupts
Shows conditions that cause each interrupt
Shows how data is gathered and passed through a downlink
Shows how command messages are received, parsed, and executed
Ideally is well suited for hierarchical breakdown into smaller processes with greater levels of detail
I've always seen interrupt timing drawn as follows:
Or inline line so:
But I prefer the former as it gives more room for annotation.
In response to your comment, perhaps a UML state machine diagram (with some adaptation) may be closer suited to your purpose:
There are many of interesting approaches you can find in diagram drawing. I will post a few here. You will find a lot of Operation System and Architecture scpecific names in there such as register , event, function names and etc. It is more for representation so far, right? So he we are.
Use UML class diagrams for showing data structures. Use sequence diagrams to show interactions between classes and interrupt service routines (showing function calls only). Use activity diagrams to show how interrupts interact with processes (signals are good for this). An activity diagram can also be used to show the process of receiving data, parsing it, and dispatching it. This can also be represented in a static view by a package diagram where the command handler is in one package and the command parser is in another, connected by a dependency line. Use cases are good for a high level view of functionality.
The main point is that UML supports many different views (static, dynamic, logical, deployment) into your system. Don't try to express everything at once.
The diagram below shows an example of an interrupt to a process.
Related
According to "Head First Object-Oriented Analysis and Design", Complex projects involves first finding a feature list -> drawing use case diagrams -> breaking into smaller modules before implementing object oriented design (requirements gathering -> use cases -> OO -> design patterns etc.)
I want to understand, what is the criteria for the size of project when feature lists and use case diagrams should be implemented before finding requirements and writing use cases?
I am particularly interested in how can this knowledge be applied to my real wold problems
Example, I am working on a UI that send instrument commands to the server and displays the response back from the server. I know from customer feedback that the UI should have the following things:
It should be able to let the user select an instrument from available list and send any custom command and display the result
It should be able to let the user select an instrument and a command from available list and display the result (create commands using drag and drops from given lists)
It should be able to have capability of creating macros
Is this UI project small enough to not have steps for gathering features and drawing use case diagrams? Do we go straight to categorizing the asks as requirements and start gathering requirements and writing use cases?
How would one go about breaking down project of this nature to deduce it to its appropriate class diagrams?
I have tried considering the above mentioned asks as features and then tried creating requirements, mainly on the different states that one could have during the life cycle of the UI application but I am still not sure and unable to comprehend the teachings of the books on this project.
I haven't read the book, so I'm not sure what the author(s) of the book really wanted to emphasize here. But I assume that you misinterpreted it.
Without knowing the requirements there is no feature list. If you don't know what is needed then you can't say anything about the system's capabilities.
Gathering requirements is an iterative process. First you gather the high-level requirements in order to be able to start building a mental model about the system. This can help you to start think about the supported features. By sharing your mental model and the exposed feature set of the system with the stakeholder, it initiates the next iteration.
Here you can start talking about actors, user journeys, use cases, etc. These are mainly focusing on the happy paths. As you have more and more iterations you will reach a point where you can start talking about edge and corner cases: What suboptimal cases can we foreseen? What can we do (prevention, detection, mitigation)? How does it affect the system/actors/journeys?...
The better you understand the needs and circumstances, the better the design and implementation of the system could be.
UPDATE #1
Will we always have high-level and low-level (edge cases and detailed use cases) requirements i.e. we will first need to make use case diagrams and then write individual detailed use cases?
There are a lot of factors which can influence this. Just to name a few:
Is it a system, submodule, or component design?
Is it a green or a brownfield project?
Is the stakeholder experienced enough to know which information matters and which doesn't from the IT project perspecitive?
Does the architect / system designer have previous experience with the same domain?
Does wireframe or mockup exist at project kick-off?
Should the project satisfy special security, legal or governmental regulations?
etc...
In short, yes there can be circumstances where you don't need several iterations, but based on my experiences that's quite rare.
I'm trying to understand how to use the FAST-RTPS libraries to implement a Command and Control application. The requirement is to allow multiple writers to direct command messages to a single reader that is tasked with controlling a piece of equipment. In this application there can be one or more identical pieces of equipment being controlled, each using a unique instance of the same reader code. I already understand that I should set the reader's RELIABILITY_QOS to RELIABLE and the OWNERSHIP_QOS to EXCLUSIVE_OWNERSHIP. The part that I am still thinking about is how to configure my application so that when a writer sends a command to the reader controlling the piece of equipment, other readers that might also receive the message will not act on it. I would like to do this at the FAST-RTPS level; that is, configure the application so that only the reader controlling the equipment receives the command message versus allowing multiple readers to receive the control message while programming these readers so that only the controlling reader will act on it. My approach so far involves assigning all controlling writers and only the controlling reader to a partition (See Advanced Functionalities in the Fast-RTPS Users Manual). There will be one of these partitions for each piece of equipment. Is this the proper way to implement my requirements or are there other, better ways?
Thank you.
Since this question was asked in under data-distribution-service, this answer references the OMG DDS specification, currently at version 1.4.
Although you could use Partitions to achieve the selective delivery that you are looking for, this would probably not be the recommended approach for your use case. The main disadvantage that comes to mind is a situation where a single writer has to send control messages to multiple pieces of equipment. With your current approach, you need a single Partition for each equipment, and you additionally need each message to be written into the right Partition. This can only be achieved by attaching a single Partition to each DataWriter, which would consequently require a single DataWriter per piece of equipment. Depending on your set-up, you may end up with many DataWriters where you would prefer to have a few, from the perspective of resource usage perspective as well as code complexity.
The proper mechanism that is intended for this kind of use-case is the so-called ContentFilteredTopic, as found in section 2.2.2.3.3 ContentFilteredTopic Class in the specification. For your convenience, I quoted some of it:
ContentFilteredTopic describes a more sophisticated subscription
that indicates the subscriber does not want to necessarily see all
values of each instance published under the Topic. Rather, it wants
to see only the values whose contents satisfy certain criteria. This
class therefore can be used to request content-based subscriptions.
The selection of the content is done using the filter_expression
with parameters expression_parameters.
Using ContentFilteredTopics, each DataReader would use a filter_expression that aligns with an identifier of the device that it is associated with. At the application level on the sender side, DataWriters would not be aware of that; they would just be writing their control messages. The middleware would take care of the delivery to those (and only those) DataReaders for which the filter expressions matches the data.
This is a core feature of many DDS-based systems. Although the DDS specification does not require it, in many cases the implementation is smart enough to do filtering on the DataWriter side, before the message goes onto the wire, in cases where that makes sense.
I do not know how much of this is actually implemented by Fast-RTPS.
I've been studying the discipline of Test Driven Development and for me it has worked well for implementing algorithms and input-output systems.
So, as far as I understand, the "essence" of TDD is to actually write tests for each requirement of the application. Normally this requirement defines a behavior with inputs and outputs.
So, now. Going to real time applications. Let´s say your application runs an infinite loop. A common example is a graphics application or an audio application where each iteration of the loop means output to the screen/speakers.
Having a system like that, let´s say the requirement is something like:
"When pressing Enter button, the screen should show a circle with the text Hello World inside the circle"
So how would you test drive this kind of requirement.
Another example, just to illustrate my question better.
Let´s say I´m emulating a CPU. In each iteration, I fetch an opcode from the file, translate it and execute it. Basically there is no actual output. What happens is there is input which changes some state related to the emulation of the CPU. So no public interface for the CPU internals.
My requirement would say something like "Implement the mov operation on the cpu emulator"
Which may be part of the bigger requirement "Implement opcodes emulation"
So. What would be a good approach for tackling this behaviors/requirements using TDD?
What would be a good approach for tackling this behaviors/requirements using TDD?
What I normally see happen is that the design partitions into two pieces
A piece that is complicated, but really "easy" to test
A piece that is hard to test, but is really "simple"
Basically, you are arranging that the "risk" lies predominantly in the code that is easy to test.
One of the properties of code that is really simple: it also tends to be very stable. The combination of low risk, stable, and difficult to test means that investing in test automation here is less attractive.
Basically there is no actual output.
The write a no-op; there's no advantage to doing any work that doesn't have an observable side effect of some sort.
It's a common pattern that we look at an intermediate stage of the output. For example, if we are supposed to produce a tone from the speakers, what we might do in code is create a seam between the work of choosing the tone, and the actual mechanism of delivering the representation of the tone to the speaker. At that seam, we also capture information so that we can check it.
So no public interface for the CPU internals.
Having a test interface is normally a satisfactory outcome. Often, it will turn out that you want to publish the test interface, for use in satisfying monitoring or observability requirements.
The public interface is way too broad to test that single behavior.
Yes, that's common. The usual response is to refactor your broad testable module into several, perhaps even many, narrow testable modules. Review Parnas 1971.
It may help also to think about the distinction between public methods (accessible outside a module) and published methods (accessible by code that you don't control).
Intro
The company I work in (it is an intern-like position though, until I am done with university) recently implemented an automated warehouse solution, where goods are transported by means of autonomous shuttles. The basic functions of the shuttles are controlled by onboard electronics (microcontroller), routing through the warehouse racking is done by software solution which in turn communicates with our ERP solution. Effectively the ERP solution handles the whole warehousing.
Task
There are well documented processes for every of the four layers (operator who loads the the shuttles, shuttle itself, routing, ERP) individually. But since we kind of puzzled all four of them together to one solution (which was kind of new to all of the participating companies), there are only vague, on-the-flyish process descriptions involving all four layers available.
Now I have been tasked to come up with a solution to illustrate the processes at work.
Example
ERP signals goods in demand at assembly station A1
Warehouse operator looks at screen and starts loading boxes to be picked up by
shuttle
Warehouse operator puts in details into ERP, such as count/weight, box number,
...
Warehouse operator clears boxes for pick-up (by confirming inputs in ERP)
ERP generates transport order
ERP sends transport order to routing software
Routing software sends telegram to shuttle control
Shuttle control turns wheels and asks for directions to pick up boxes
...
Question
As mentioned, I have to graphically represent the kind of processes similar to the one shown in the (easy and not complete) example above. I need to incorporate the operator's actions as well as basic communication between shuttle, routing software and ERP.
Since I attended a course on BPMN at university it came to mind immediately. But now, after immersing myself into information about BPMN for several hours I still can't conclusively tell if BPMN helps my efforts or just further complicates the whole thing.
Is BPMN the right tool for my purpose?
Disclaimer
I am not a Business Analyst. I have looked at alternatives to BPMN (simple flowcharts, activity diagrams, ...) but they don't seem to fit.
Just putting together the existing processes for every respective layer yields no result, owing to the different and sometimes too detailed process descriptions.
Edit
The ERP is SAP ERP 6.0 EHP7 with integrated WMS component.
TL;DR: use the notation you would be implement process in, i.e. choose BPMS, not BPMN.
The notation itself means nothing unless it has proper tool for modelling and further process implementation aka BPMS. You can find dozens of comparisons (e.g. BPMN vs EPC or BPMN vs BPEL), however they won't help you unless you have clear understanding where and how you will be implement you modeled process.
Generally speaking, EPC is used for more high-level view of the process, whereas BPMN is utilized for more fine-grained view, where all technical details of communications between peers can be described. However, it depends.
I also recommend you to review this table
and answer the question to yourself whether your process changes (in)frequently or not, and whether you need separate BPM tool.
How I see it from your description: you have four participants (four layers), which are four lanes in BPMN terms, and they are collaborating/communicating with each other during the process. Generally speaking, this fits to BPMN application area, but personally I feel that you should stick your ERP tooling. I don't know which ERP you use, but every serious ERP solution includes tool for process customization. For example, SAP has Workflow,
which can widely enhance and extend existing processes within SAP. Probably, your ERP have it too.
Again, it's not clear which warehouse management system you use and if it is integrated to your ERP. It seems to be not, and it seems to be some old legacy system, because of which you start re-modelling the stuff. In this particular case it might me wiser to acquire special advanced warehouse management package (take a look at SAP's EWM features as an example) which can cover most of your requirements.
We have a number of processes that rely on interactions between two people/groups. I am trying to figure out the best way to illustrate this in BPMN.
CONSIDER:
Using the example of a pizza order, I call a pizzeria to order, an order-taker answers the phone and then we discuss my order. I am trying to accurately capture the "we discuss the order" portion of the process. Here is how I envision the diagram playing out. I call, they answer, then there's branching for a simultaneous exchange, which converges at the end of the call and my order is finished. Is this illustrated correctly? or are there better ways to show that two different entities communicating with each other at the same time to accomplish a task?
The moment you want to show interaction in greater detail than high level bird view, you typically run into troubles when remaining within the paradigm of using "one pool with several lanes". In such a case you need to draw a so called "collaboration diagram", which means you make use of several pools and hence several process definitions interacting with each other by means of message exchange. I give you an example here:
You may use those envelope symbols attached to the message flows, but you don't need to.
The big advantage of that approach is that you can now show that those processes are dependent on each other, yes, but each participant also wants to remain in drivers seat of his/her own process, e.g. by deciding what to do if the other side doesn't provide the desired answer, doesn't do anything within a reasonable time and so on. Furthermore you can look at that diagram from both perspectives and people will actually see "their own process" - and not something mixed with the concerns of others involved.
For that same reason BPMN also offers the concept of "collapsed pools" to be able to look just at the communication from one side and treat the internal details of the other side as a kind of "black box":