My Question may be simple, but I am confused because I have no idea about activity diagrams.
My question- Are multiple end points ever acceptable in an activity diagram?
It's a bit touchy to reference IBM though they are one of the big OMG parents. The "truth" is written in OMG's superstructures.
Actually UML2.5 talks about Final Node in the context of activity diagrams:
Final Nodes
A FinalNode is a ControlNode at which a flow in an Activity stops. A FinalNode shall not have outgoing ActivityEdges. A FinalNode accepts all tokens offered to it on its incoming ActivityEdges.
There are two kinds of FinalNode:
A FlowFinalNode is a FinalNode that terminates a flow. All tokens accepted by a FlowFinalNode are destroyed. This has no effect on other flows in the Activity.
An ActivityFinalNode is a FinalNode that stops all flows in an Activity ...
A ControlNode is a kind of ActivityNode and those form Activities. The definition except in the context of the FinalNode does not tell how the single ActivityNodes can be related. So from that you can have as many as you like/need.
Yes, there may be cases where multiple endpoints are acceptable.
It is possible for an activity diagram to show multiple final states.
Unlike initial state symbols, of which there can be only one on an
activity diagram, final state symbols can represent the termination of
one of many branches in the logic -- in other words, the activity may
terminate in different manners.
https://www.ibm.com/developerworks/rational/library/content/RationalEdge/sep03/f_umlbasics_db.pdf
(Page 5)
Other Resources-
http://iswwwup.com/t/08d7e57730dc/uml-do-activity-diagrams-always-end-in-one-endpoint.html
https://softwareengineering.stackexchange.com/questions/215071/do-activity-diagrams-always-end-in-one-endpoint
I am trying to create design document for a project which has all background processes in it.
The sequence of background processes are as follows:
Process P1->
Get all records(thousands) from database.
Analyze validity of records.
Send valid records to process P2.
Process P2 ->
Get valid records one by one.
Do first level processing of data.
Send this to process P3.
Process P3 ->
Get records one by one from process P2.
Based on processing results, update records in database.
I am trying to decide which diagrams to create in this case. Particularly, I am confused about Use Case Diagram. What will be the actor here? Is UseCase diagram even applicable in case of such background processes.
Describing a process is usually done with an activity diagram. If you want to describe a particular execution you should use a sequence diagram.
For a background process a use case isn't applicable I thought? User has no direct interaction with the process, unless you have it interfacing with some trigger that the end user controls.
Activity, Sequence Diagrams and Class Diagrams should be sufficient for your needs.
I am new to the world of UML and have so far learnt the basics of use case, activity and deployment UML diagrams. I have a requirement of where users interact with a system e.g. user sending an email, which is then processed by a system and then sent to an agent (person) who then responds and interacts once again with a system.
I am having a hard time picturing these requirements and whether it should be a combination of use case, activity or deployment. Can I intermingle them? What is standard practice?
As you know, use cases are used to capture requirements. When identifying and detailing use cases, you look at the problem from the perspective of users. Only focus on what an actor expects the system to do. First step is to identify the use cases and actors and then detail the use case flows.
1- Identify the use cases and actors
In your example send email could be a use case initiated by the end user (your actor). What happens next (e.g system sending a notification to the agent) could be modeled as part of the flow of this use case.
Another use case could be the agent actor handling what they have to do after receiving the notification from the system (a prerequisite of this use case could be that a notification has been received).
Note that you could combine these two use cases together and have the agent as a secondary actor (secondary actor interacts with the use case but does not initiate it). Whether you do this or not, is a modeler's choice and depends on the size of use cases, number of use cases and many other things.
2- Detail the use cases
After identifying use cases and actors, you should detail use cases. The most important part is to detail the use case flow (step by step interactions of actor and system). This can be written as text or drawn as an activity diagram.
So to answer your question: yes it is possible and very common to combine activity diagrams and use cases; that is an activity diagram drawn to show the flow of steps of a use case.
Deployment diagrams on the other hand are totally irrelevant to the requirement elicitation phase. They model the physical structure of the system and how hardware components and software components interact.
In fact, it is very odd that you have learned component diagrams before class diagrams, sequence diagrams, state diagrams and many other diagrams.
I need to know this differences in order to undestand how to use them right.
Which are the differences of DFD and Activity diagram?
Actually, it's reasonably logical. You only have to look at the names.
In data flow diagrams, the lines between "boxes" represent data that flows between components of a system. Because these only show the flow of data, they do not give an indication of sequencing.
In activity diagrams, those lines are simply transitions between activities and do not represent data flow at all. They more represent the sequencing of activities and decisions. You can tell from these what order things happen in.
That's a simplistic explanation but should be a good starting point. Further information can be garnered from Wikipedia for DFDs and activity diagrams.
Explicit bias: I'm a DFDs proponent.
#John is correct that Activity diagrams can be used to represent object flow. #pax equally correct they seldom are.
Two big DFD advantages for me:
Link to object model. Data stores on a DFD provide a really nice way to link the data produced / consumed to the object model. Very useful for consistency and ensuring your thinking is joined up.
They de-emphasise control flow. Far too often designs over-constrain sequencing. Activity diagrams do support concurrency - but it requires the user to (a) remember and (b) use it. So the default is over-serialisation. DFDs don't. They lay bare the real sequence dependencies without any extra effort on the part of the user. Consequently they also make it easier to see causal relationships. If processes a and b both require data input D then it's obvious on the diagram. And hence parallel activity is obvious.
Don't get me wrong - I'm not against Activity diags. Where control flow is the primary consideration I'll use an AD over a DFD. But empirically I'd say I find DFDs a more useful tool in ~70-80% of cases.
Of course, YMMV.
Just a humble opinion from someone who has had to explain processes, both computer and manual, to upper management and CIOs. I have found simple is better and pound-for-pound, DFDs get the message across when I am actually "asked" about details. That being said, the better approach is to always practice the story line and answer in simple answers.
One final comment regarding the age of tools and products. Remember that in most cases these are running the business and work pretty darn good. The adage "you break it (or replace it) and you own it" can make you a hero or make you into a clown.
We have a CIO who wants to replace all mainframe application for the simple reason that they are old technology. One must weigh the consequences and understand if the replacement can handle workload. Have you ever wondered why JPMC, Credit Swiss, Walmart, and Bank of America to name a few still run mainframes?
My apologies for taking it in that direction. Just make sure, whatever analysis tool is used, that all aspects of the replacement are documented including workload, I/O, concurrent users, adoption curve, and scalability.
Data Flow represents flow within one module or one independent code. However Sequence Diagram represents sequence of activity in between different modules.
Yes at some points they may pass the same messages.
I basically use Sequence diagram in interface documents which will be shared with other modules/elements, however DFD will be used in Low level design documents which will be used to develop the code within one module or network element.
If we look closer to a dataflow diagram, we can notice that when a node collects data from all its edges, it starts to process them. And to process, it needs an activity token, which represents access to a processor. Usually the process of obtaining that token is omitted, but it has to exist. Typically, the whole node as a token is put in a double-ended queue, where on the other end of that queue free activities (processors or threads) are stored. A thread pool is a perfect example of such a queue, and the nodes ready to work are represented as tasks. As soon as a node meets activity, they both are taken from the queue and actual processing starts. When processing finishes, activity is returned to the queue. This way we can think of activity as a special kind of token.
So both dataflow and activity diagrams are just simplified variants of a general active-data-flow diagram, with either activities or data tokens omitted. But generally, both kinds of tokens can be represented in a diagram simultaneously.
Programmers used to think about threads as activities, but if we look at them closer, we notice that when a thread is ready to execute, it gets in a line to processors, and real execution starts only when a free processor switch to that thread. This is absolute analogy as tasks are executed on a thread pool. So from simplified point of view, a thread is an activity, and from more rigorous point of view a thread is a data token and the only real activity is a physical processor. This shows that activity tokens are not different from data tokens. And indeed, we can omit the route of node chasing an activity and consider a dataflow node as an activity itself, which starts to work immediately when all its edges (inputs) contain data.
If you believe that a use case flow of events creates an actor, how would you model that?
I have a use case that creates a windows service, which (in my mind) is another system with its own set of use cases and actors.
At the moment it is not obvious from the use case diagram that an actor gets created as part of the flow of events.
Aidan.
Use case diagrams do not display a sequence of actions. There is no time dimension. As a result, it makes no sense to create or delete an actor.