Here is an image of my first cut sequence diagram:
My question is this: the retrieveStockInfo(stkID,stkInfo) method gets the data that is wanted to be shown to the customer. At the moment, I have a response to the activation 'box'. Is this correct? Do I need to return anything else to the actual Customer?
thanks
Yes, you need to return the information to the customer otherwise they will never know what happened!
You might also want to put in error handling sequences. These are often forgotten about in sequence diagrams.
Related
I am new in doing an activity and currently, I am trying to draw one based on given description.
I enter into doubt on a particular section as I am unsure if it should be 'split'.
Under the "Employee", the given description is as follows:
Employee enter in details about physical damage and cleanliness on the
machine. For the cleanliness, there must be a statement to indicate
that the problem is no longer an issue.
As such, I use a foreach as a means to describe that there should be 2 checks - physical and cleanliness (see diagram in the link), before it moves on to the next activity under the System - for the system to record the checks.
Thus, am I on the right track? Thank you in advance for any replies.
Your example is no valid UML. In order to make it proper you need to enclose the fork/join in a expansion region like so:
A fork/join does not accept any sematic labels. They just split the control flow into several parallel ones which join at the end.
However, this still seems odd since you would probably have some control for the different inspections being entered. So I'd guess there's a decision which loops through multiple inspection entries. Personally I use regions only for handling interrupts. ADs are nice to a certain level. But sometimes a tabular text (like suggested by Cockburn) is just easier to write and read. Graphical programming is not the ultimate answer (unlike 42).
First, the 'NO' branch of the decision node must lead somewhere (at the end?).
After, It differs if you want to show the process for ONE or MULTIPLE inspections. But the most logical way is to represent the diagram for an inspection, because you wrote inspection without S ! If you want represent more than one inspection, you can use decision and merge node to represent loop that stop when there is no more inspection.
I would like to ask, if a final node in some activity can represent two different outcomes.
For example in use case buy premium account I can have two outcomes: IF I have enough credit then I will end the activity with bought premium account ELSE I end the activity with some error page that the user doesn't have enough credit.
Can I use the same final node in this case?
Yes you can with something like the image
More see the comment about in UML specification: "In Figure 15.44, two ways to reach an ActivityFinalNode exist; but it is the result of exclusive “or” branching, not a “race” situation like the example in Figure 15.43. This example uses two Activity FinalNodes, which has the same semantics as using one with two incoming edges."
It means that a FinalNodes may have two incoming edges, and the norm explains that the first flow which reaches the FinalNode terminates the activity what ever the other flow, and there is something special for output activity parameters.
I'm working on a problem that at the very least seems to require named entity recognition, but I'm not sure how to go farther than the NER parse. What I'm trying to do is parse information (likely from tweets) regarding scheduling of events. So, for example, I'd like to be able to automatically resolve the yes/no answer to the question of "Are The Beatles playing tomorrow?" from short messages like:
"The Beatles cancelled their show tomorrow" or
"The Beatles' show is still on tomorrow"
I know NER will get me close as it will identify the band of interest and the time (if it's indicated), but there are many ways to express the concepts I'm interested in, for example:
"The Beatles are on for tomorrow" or
"The Beatles won't be playing tomorrow."
How can I go from an NER parsed representation to extracting the information of interest? Any suggestions would be much appreciated.
I guess you should search by event detection (optionally - in Twitter); maybe, also by question answering systems, if your example with yes/no questions wasn't just an illustration: if you know user needs in advance, this information may increase the quality of the system.
For start, there are some papers about event detection in Twitter: here and here.
As a baseline, you can create a list with positive verbs for your domain (to be, to schedule) and negative verbs (to cancel, to delay) - just start from manual list and expand it by synonyms from some dictionary, e.g. WordNet. Also check for negations - again, by presence of pre-specified words ('not' in different forms) in a tweet. Then, if there is a negation, you just invert the meaning.
Since you work with Twitter and most likely there would be just one event mentioned in a tweet, it can work pretty well.
If CQS prevents commands from returning status variables, how does one code for commands that may not succeed? Let's say you can't rely on exceptions.
It seems like anything that is request/response is a violation of CQS.
So it would seem like you would have a set of "mother may I" methods giving the statuses that would have been returned by the command. What happens in a multithreaded / multi computer application?
If I have three clients looking to request that a server's object increase by one (and the object has limits 0-100). All check to see if they can but one gets it - and the other two can't because it just hit a limit. It would seem like a returned status would solve the problem here.
It seems like anything that is request/response is a violation of CQS.
Pretty much yes, hence Command-Query-Separation. As Martin Fowler nicely puts it:
The fundamental idea is that we should divide an object's methods into two sharply separated categories:
Queries: Return a result and do not change the observable state of the system (are free of side effects).
Commands: Change the state of a system but do not return a value [my emphasis].
Requesting that a server's object increase by one is a Command, so it should not return a value - processing a response to that request means that you are doing a Command and Query action at the same time which breaks the fundamental tenet of CQS.
So if you want to know what the server's value is, you issue a separate Query.
If you really need a request-response pattern, you either need to have something like a convoluted callback event process to issue queries for the status of a specific request, or pure CQS isn't appropriate for this part of your system - note the word pure.
Multithreading is a main drawback of CQS and can make it can hard to do. Wikipedia has a basic example and discussion of this and also links to the same Martin Fowler article where he suggests it is OK to break the pattern to get something done without driving yourself crazy:
[Bertrand] Meyer [the inventor of CQS] likes to use command-query separation absolutely, but there are
exceptions. Popping a stack is a good example of a query that modifies
state. Meyer correctly says that you can avoid having this method, but
it is a useful idiom. So I prefer to follow this principle when I can,
but I'm prepared to break it to get my pop.
TL;DR - I would probably just look at returning a response, even tho it isn't correct CQS.
Article "Race Conditions Don’t Exist" may help you to look at the problem with CQS/CQRS mindset.
You may want to step back and ask why counter value is absolutely necessary to know before sending a command? Apparently, you want to make decision on the client side whether you can increase counter more or not.
The approach is to let the server make such decision. Let all the clients send commands (some will succeed and some will fail). Eventually clients will get consistent view of the server object state (where limit has reached) and may finally stop sending such commands.
This time window of inconsistency leads to wrong decisions by the clients, but it never breaks consistency of the object (or domain model) on the server side as long as commands are handled adequately.
Hi can anyone tell me their thoughts on this sequence diagram, if it is correct or whatever needs changing.
Thankyou, your feedback would certainly help a lot.
Full Size Image: http://i.stack.imgur.com/ktPsY.jpg
There seem to be some splits in the sequences, for example there is a gap between steps 2 and 3. Keeping each sequence whole makes the diagram valid and much more readable. Here is an example of what a diagram should look like. Note how the bar for the customer goes on until the very end of the sequence.
The objects have also been chosen pretty confusingly. Aren't Register, Login and Book part of the web server? If they are, you probably should get rid of the Web Server object in this chart.
The return values should be passed back to the object that originated the call like has been correctly done in steps 11 and 12, though there is another gap in the sequence.
Some sequences are incomplete, like step 8. Now the diagram describes the Browse Shows as a call that is made by the user to the Book object, which never provides any return value.
The alternate paths 4 and 5 are incorrectly defined. An else block should be used instead.