I build a UML state diagram and have a case where same transition to specific state exists from most of other states.
What is the most elegant solution to draw it?
Currently I though about two options:
1) Use junction pseudo-state with exit to my target state
2) Wrap source states in a composite and make a transition from it
Better ideas appreciated
Both solutions would be appropriate, depending on their legibility on the diagram. Too many transitions tend to clutter a diagram and make it difficult to read.
So if you have just a few source states (say less than 4), using transitions to a junction pseudostate (not a join pseudostate - different semantics!), it should be fine. The down side to this solution is that, if you want to get back to the original source state, you will have to store the information (e.g., as part of the signal).
If you have more, you can consider a composite state for all your source states. Note that if you do this, you can also have a transition to history to get back to the sub-state that was left, which may make your state diagram logic easier to implement (no need to store the state left) and the diagram easier to read.
I hope this helps.
Related
What are the differences and similarities between the state machine diagram and flowchart?
So far I found that the state diagram shows us the actual change in the state, not the process or commands like in the flowchart.
In a state diagram, the nodes are states and the arrows correspond to something that happens that triggers a change of state.
In a flow chart, the nodes are actions or decisions, and the arrows correspond to the flow of control, i.e. what happens next. Flow chart are not UML. The closest UML diagram is an activity diagram that allows you to meodell more precisely everything you can model with a flow-chart and more (since the arrows can also represent an object flow).
Both can be complementary: an action/decision in a flow-chart could trigger events that cause changes of state. But it's not necessarily one for one: an action may cause several state changes without any evidence in the flow-chart that these may happen.
Short and simplified example:
Imagine an Order object. It may have the state received, delivey in preparation, delivery complete, invoiced. Each of these state tells what can happen next with the order. That'll be a topic for astate diagram.
Imagine a flowchart. These are different actions happening in sequence: Get an order from customer, Pick items of the orders from the inventory, Send items to the customer, Are all items sent?, if yes, Prepare and send invoice, if no, Find missing items and then go back to Pick items ... and continue from there.
As you see: both can tell the same story, but from a different angle with different details.
As you mentioned, a State Machine Diagram focus on display from which state to which state the execution goes based on the input.
Although a State Machine can be handled as a specialized form of a flow chart / activity chart.
What happens in an UML state machine if the transition selection algorithm (TSA) finds two transitions that should both fire and the following holds true:
transition #1 ends directly in a state
transition #2 ends (intermediately) in a choice pseudostate
As both the transitions fire, they cannot be in conflict. Else they would not have been chosen by the TSA in the first place.
Now the following occurs:
As the choice is evaluated (after transition #2), it takes a path (transition) that would lead to the exit of an ancestor state of the source state of transition #2. Due to this exit of an ancestor state, a conflict with transition #1 occurs.
UML diagram showing such a situation
(improved according to the discussion with Thomas Kilian in comments to his (now deleted) answer)
... if Event_1 occurs and x < 0.
Questions
Is the state machine ill-formed or what is supposed to happen now?
Is it illegal for a transtions after a choice to exit a state? At least it doesn't play together well with the "transition execution sequence" (exit(s), transition behavior(s), enter(s)). As it would be exit, behavior, exit, behavior, enter(s) in that case. I could not find anything about that in the UML Superstructure Specification (chapter 15). But then everything about orthogonal regions is very vaguely described in that document...
Motivation
I am asking the question out of the perspective of a library implementer. So my focus is not on how to design this situation in a nicer manner. I need to figure out how to deal with this situation correctly (or I need to know that it is an illegal situation).
This is one reason why there is a "Precise Semantics of UML State Machine" at the OMG...
First, it is legal for most transitions to exit a state. There are a few restrictions in the UML spec, but none that would concern your design.
You should always have a single state that is potentially active within any state machine region. As it stand, you have an implicit region in your "StateMachine1" that contains both the "X" and"Y" states. This would mean that your state machine could be in both "StateMachine1::X" and "StateMachine1::Y" states at the same time! As you probalby already know, orthogonal states are there do deal with such a situation. Perhaps you need to bring "X" and "Y" within state StateMachine1::S' regions?
Also a warning that by default in UML, states have shallow history. This means that, as it stands, the initial transitons within StateMachine1::S' regions will only be taken once. If you try to get back into "S" (I know, you don't have a transition for that - just speculating), it will go back to the last states (one per region) before if left the state, which, after event1, would be "A" and "E".
It would be difficult to comment more without knowing what you are trying to model, but I hope this helps.
Is it "legal" to for the only transition out of a composite state to originate from a decision node as shown in the picture?
http://pokit.org/get/?7358c1cf25ccd026b9ebe528768b0eb5.jpg
Yeah, I know the writing seems like I'm speaking in tongues. :) Apart from that, does the diagram make sense like this and is it valid according to UML rules?
Thank you for your time!
For full UML (2.5) compliance, you would need entryPoint and exitPoint pseudostates when you enter or exit a state. However, these are often not shown when there is no transition to/from a substate or when hierarchical state history is not tracked.
So you would need an entryPoint pseudostate on the Zapoceta state that would act as the "bridge" between the initial point and the Nepotpuna states.
Similarly, you would also need an exitPoint pseudostate in the Zapoceta state that would act as the "bridge" between the choice pseudostate and the Potpuna state.
Also, you would not need an "or" constraint on the transitions between the Obracunata and Placena states. What you would have are different triggers for each transition. Having multiple transitions out of a state machine implies that the transitions' triggers are mutually exclusive.
My requirement : I want to come up with a suitable UML diagram based on the case which is described below. I need to know which UML will best suit this condition.
The case : Two object A and B in the form of "Application Forms" interacts with each other.Certain event in object A triggers a state change of object B.Both object interacts with each other for a Use Case.
I tried using State Diagram but it fails as here 2 object interact with each other to change the state of one object, whereas State diagram is suitable to depict state change of one object only without showing interaction with another object which is causing state change.
My requirement is to show both interaction and state change together in the same diagram.Is it possible?
Any suggestion on this which UML diagram is suitable for this?
UML uses two different diagrams for each behavior, one for State (State Machine Diagram) and one for Interaction (could be the communication diagram or the sequence diagram).
Since the Interface of a class doesn't change when it's state changes (by applying the State Pattern for example), the interaction should not really change from the perspective of the caller, sure, internally all kinds of things might be going on, but that should not really matter.
The way I'd model this is to describe which states your objects are in and which scenario will play out. That will result in a few interactions and possibly state changes. Then pick a new scenario, either using the end-state of the previous one as a starting point, or describing a new starting state.
That way each scenario is clearly defined, the interaction diagram shows how the objects interact, and multiple State Diagrams with the active state highlighted can show the changes in state and thus behavior of the different objects.
There is no diagram that gracefully combines both, since one (the state machine) is a static diagram, showing all possible options, while the other describes the interaction.
Sure you could play around with creative naming, as suggested (ObjectA/State) as your different objects in the interaction type diagrams, but it would not result in a very clear picture. What you're trying to describe here is a story, a sequence of events and how those events impact the different states of the objects. So your scenario's are the story on a high level, the communication diagrams the stories on a much more detailed level and the state machine diagram the snapshots of specific situations.
Model your states in the state diagram as such: (Object / ObjectState).
For example:
States (A/uninitialized) , (A/initialized), ...
Should work then.
State diagram, sequence diagram, communication diagram and the whole answer by #jessehouwing is fine, but I think there is an easier and more natural way:
(1) http://agilemodeling.com/style/activityDiagram.htm, Figure 3. Submitting expenses
Note that this is UML 1.4 activity diagram. Current UML notation is slightly diferent. Dashed lines represent Object flow : Chapter 3.90.2.2 Object flow ...Objects that are input to or output from an action may be shown as object symbols. A
dashed arrow is drawn from an action state to an output object, and a dashed arrow is drawn from an input object to an action state. The same object may be (and usually is) the output of one action and the input of one or more subsequent actions...
and (2) http://www.uml-diagrams.org/document-management-uml-activity-diagram-example.html
show an examples of how you can combine object states and UML activity diagram. The pictures are activity diagrams and the orange rectangles highlight points where objects with states (the part in [some state]) are shown. The purple rectangles show authors who were robbed.
I am really unable to understand the real difference between these 2 diagrams. I mean both of these deal is "states" but I am not sure what deals with what?
It might seems so, but the difference is, activity diagrams describe activities and state charts describe states. So those models are orthogonal - you might imagine there is an activity between two states (something that occurs during the transition) and you might say there is a state between two activities. This is rather a simplification, but I think it might suffice to explain the difference, which is primarily focus, both diagrams are for describing behaviours.
An activity diagram is a special case of a state chart diagram in which states are activities (“functions”).
Two types of states:
– Action state:
-- Cannot be decomposed any further.
-- Happens “instantaneously” with respect to the level of abstraction used in the model
– Activity state:
--Can be decomposed further
--The activity is modeled by another activity diagram
For examle an elevator ride.
State chart could contain states such as: entering, standing still, exit, arrived.
These state transitions are caused by activity diagram events.
And events in activity diagram could be:
Walk in to the elevator, push button to correct floor, walk out of the elevator.
I would say these two diagrams overlaps each other.
Activity diagram is used to document the logic of a single operation/method, a single use case or the flow of logic of a business process. It is equivalent to flowchart and data flow diagram from structured development.
The state diagram depict (show)the state of objects as their attributes change from state to the other state. State chart modeling is used to show the sequence of states that an object goes through, the cause the transition from one state to other and the action that result from a state change.
Activity diagram is flow of functions without trigger (event) mechanism, state machine is consist of triggered states.