1. Graphical Systems Modeling with UML / SysML Sequence diagrams
ca. 30 min.
© Piotr Ciskowski

2. State machine diagrams – lecture plan:
Overview GO
Basic elements GO
Advanced elements GO
Combined fragments GO
Summary GO
Examples GO
lecture plan

3. Perspectives - views: Dynamic View Logical view Use case view
architecture
class diagram
object diagram
composite structure diagram
package diagram
behavior
sequence diagram
activity diagram
state machine diagram
interaction overview diagram
communication diagram
timing diagram
package diagram
Dynamic View
Logical view
Use case view
Deployment View
system scope & functionality
use case diagram
package diagram
Implementation View
hardware
deployment diagram
package diagram
software
component diagram
package diagram

4. Sequence diagram
describes interactions between instances as sequences of messages passed between them
documents functionality of a use case

5. Sequence diagram
describes interactions between instances as sequences of messages passed between them
documents functionality of a use case
shows:
flow of control
order and location of performed operations
exchange of messages between objects – chronologically
logic of methods and services

6. Sequence diagram
describes interactions between instances as sequences of messages passed between them
documents functionality of a use case
shows:
flow of control
order and location of performed operations
exchange of messages between objects – chronologically
logic of methods and services
close to code

7. Sequence diagram
describes interactions between instances as sequences of messages passed between them
documents functionality of a use case
shows:
flow of control
order and location of performed operations
exchange of messages between objects – chronologically
logic of methods and services
close to code
horizontally - classifiers’ instances
vertically - time

8. Sequence diagram
describes interactions between instances as sequences of messages passed between them
documents functionality of a use case
shows:
flow of control
order and location of performed operations
exchange of messages between objects – chronologically
logic of methods and services
close to code
horizontally - classifiers’ instances - statics
vertically - time - dynamics

9. Sequence diagram types of diagrams – levels of detail / abstraction:
conceptual - general scope - evident interactions

10. Sequence diagram types of diagrams – levels of detail / abstraction:
conceptual - general scope - evident interactions
implementational - very precise - all types of elements - main flow and all alternative flows - complete specification - for programmers / CASE tools
instance - implementational for a certain scenario

11. Sequence diagram basic elements

12. Basic elements: objects, actors (classifiers’ instances) lifelines
As lifeline is always linked to one element (actor or object), some people treat it as one and call the pair (object, lifeline) a lifeline
A lifeline usually has a rectangle containing:
object name (and its class)
class name (anonymous object)
„self” – classifier which own the sequence diagram
image: Sparx Systems – UML 2 Tutorial

13. Basic elements: objects, actors (classifiers’ instances) lifelines
messages

14. Basic elements: objects, actors (classifiers’ instances) lifelines
messages
activation - focus of control - object active / inactive

15. Basic elements: objects, actors (classifiers’ instances) lifelines
messages
in this diagram anonymous objects of Computer and Server classes interact
image: Wikipedia

16. Basic elements: objects, actor, lifelines, messages:
Client
PINpad
Screen
ATMinterface
BankSystem
ChipCard
getPIN()
enterPIN
verifyPIN()
showOperations()
checkBalance
checkAccountBalance()
showBalance()
in this diagram the notation of objects (their names) is rather conceptual

17. Sequence diagram advanced elements

18. Advanced elements on detailed implementation diagrams:
different types of messages
creating and destroying objects
conditions
messages to self (self messages)
duration and time constraints
combined fragments
interaction uses
gates

19. Advanced elements
Messages

20. Messages synchronous call asynchronous call asynchronous signal reply
synchronious
send message, suspend execution, wait for response
asynchronious
no waiting for response
reply
sending back the focus of control to the sender after a synchronious call
optional
image: Sparx Systems – UML 2 Tutorial

21. Messages synchronous call asynchronous call asynchronous signal reply
self
image: Sparx Systems – UML 2 Tutorial

22. Messages synchronous call asynchronous call asynchronous signal reply
self
create
delete
image: Sparx Systems – UML 2 Tutorial

23. Messages synchronous call asynchronous call asynchronous signal reply
self
create
delete
create message may have a «create» stereotype
image:

24. Messages synchronous call asynchronous call asynchronous signal reply
self
create
delete
lost
found
Two types of messages used in conceptual phase:
lost
receiver temporarily unknown
to be completed later
found
sender out of the diagram
sent by a phenomenon
image: Sparx Systems – UML 2 Tutorial

25. Advanced elements
Other elements

26. Other elements
conditions - mesage executed if condition satisfied - usually one message – one condition
Buyer
IAuction
[bidPrice > minBidPrice] : joinAuction()
example based on: Wrycza et al., Język UML 2.0 w modelowaniu… (modified)

27. Other elements conditions
iterations - multiple execution * < operation > * [ < iteration specification > ] < operation >
IProjectManager
WorkerDatabase
*[worker := 1..n] : assignSpecialist()
example based on: Wrycza et al., Język UML 2.0 w modelowaniu… (modified)

28. Other elements conditions iterations
forks - at least two disjoint conditions
Seller
IUserPanel
ProductCatalogue
Auction
cancelAuction(reason)
[reason = withdrawArticle] : deleteArticle()
[reason = cancelAcution] : endAuction()
example based on: Wrycza et al., Język UML 2.0 w modelowaniu… (modified)

29. Other elements
forks - at least two disjoint conditions - with receiver’s lifeline split
Buyer
CFDcontract
Broker
Bank
closePosition()
updateValue()
[currentValue > nominalValue]:closePosition()
transferProfit()
[currentValue < nominalValue]:closePosition()
deductLoss()
transferDeposit()
confirmClosedPosition()
CFD – Contract For Difference – kontrakt różnic kursowych – main type of instruments on forex markets
example based on: Wrycza et al., Język UML 2.0 w modelowaniu… (modified)

30. Other elements conditions iterations forks
constraints (time & duration)
Duration and Time Constraints:
By default, a message is shown as a horizontal line
Since the lifeline represents the passage of time down the screen, when modelling a real-time system, or even a time-bound business process, it can be important to consider the length of time it takes to perform actions
By setting a duration constraint for a message, the message will be shown as a sloping line.
image: Sparx Systems – UML 2 Tutorial

31. Advanced elements
Combined fragments

32. Combined fragments
combined fragment - part of sequence diagram enclosed in a frame executed under specific circumstances - adds procedural logic
sequence diagrams are not intended for showing complex procedural logic
but there are a number of mechanisms that do allow for adding a degree of procedural logic to diagrams – combined fragments

33. Combined fragments
combined fragment - part of sequence diagram enclosed in a frame executed under specific circumstances - adds procedural logic
operator - how to interpret
operand - what to do
sequence diagrams are not intended for showing complex procedural logic
but there are a number of mechanisms that do allow for adding a degree of procedural logic to diagrams – combined fragments

34. Combined fragments alt - alternative - if–then-else - switch
execution of one and only one of a few operands
image:

35. Combined fragments opt - option - alt with only one operand
optional execution of the (only one) operand
image:

36. Combined fragments
break - breaking or exceptional scenario - performed instead of other interactions
only one operand
on execution of this operand, all other interactions of the enclosing interaction fragment are ignored
in this case all remainding operations in the loop would be ignored
image:

37. Combined fragments loop - iteration loop (n) loop (min,max) loop
operand is repeated for a specific number of times:
strictly n times
lower and upper number of iterations
no parameters = infinite loop
images:

38. Combined fragments neg - invalid series of messages
invalid actions – exceptions that must be served
e.g.:
arythmetic operation error
index out of range
invalid data type
stack overflow
etc.
After www-uml-diagrams.org:
Negative traces are the traces which occur when the system has failed
All interaction fragments that are different from the negative are considered positive, meaning that they describe traces that are valid and should be possible
In this example:
Should we receive back timeout message, it means the system has failed
image:

39. Combined fragments par - parallel, concurrent processing
all operands are processed concurrently
image:

40. Combined fragments par - simplified notation
image:

41. Combined fragments
critical - critical section - highest priority - object „reservation”
critical section – gets the highest priority during execution of the whole interaction
instance classifiers, enclosed in critical section, are not allowed to take part in other interactions
interactions surrounding the critical section, not disturbing it, may be processed concurently
After
A critical region is a region with traces that cannot be interleaved by other occurrence specifications (on the lifelines covered by the region)
This means that the region is treated atomically by the enclosing fragment and can't be interleaved, e.g. by parallel operator
In this example:
Add() or remove() could be called in parallel, but each one should run as a critical region.
image:

42. Combined fragments
consider - ignore consider { <messages> } ignore { <messages> }
consider
defines which messages should be considered within the combined fragment = all others will be ignored
ignore
defines which messages are of no interest if they appear in the current context
seems obscure – but may be used to specify a test of an existing system (at runtime messages ignored during tests will be executed)
images:

43. Combined fragments strict - strict order (sequencing)
the order, in which the messages are executed – cannot be changed
image:

44. Combined fragments seq - weak sequencing
encloses a number of sequences for which all the messages must be processed in a preceding segment before the following segment can start, but which does not impose any sequencing within a segment on messages that don’t share a lifeline
messages on different lifelines – may be executed in any order
After
The ordering of occurrence specifications within each of the operands is maintained
Occurrence specifications on different lifelines from different operands may come in any order
Occurrence specifications on the same lifeline from different operands are ordered such that an occurrence specification of the first operand comes before that of the second operand
In this example:
Search Google possibly parallel with Bing and Yahoo, but search Bing before Yahoo
image:

45. Combined fragments ref - other interaction use
allows to use (call) another interaction
reference to another diagram
simplifies large and complex interaction diagrams
allows for reusing some interaction between several other interactions
referenced interaction has formal gates
interaction use provides a set of actual gates that must match the formal gates of the interaction
images:

46. Combined fragments: alt - alternative opt - option
break - breaking or exceptional scenario
loop - iteration
neg - invalid actions
par - parallel processing
critical - critical section, highest priority
consider, ignore
strict, seq - strict order, weak sequencing
ref - reference to other interaction

47. Summary

48. Sequence diagram
Summary:
image:

49. Sequence diagram Steps: analyze use cas scenario
identify classifiers to take part in the interaction
create conceptual diagram:
classifiers’ instances – horizontally
ordered messages - vertically
execution boxes
create implementation diagram:
all other details, advanced elements and full specifications needed
create instance diagram

50. Examples

51. Examples for discussion Facebook User Authentication in a Web application source:
after
An example of sequence diagram which shows how Facebook (FB) user could be authenticated in a web application to allow access to his/her FB resources.
Facebook uses OAuth 2.0 protocol framework which enables web application (called "client"), which is usually not the FB resource owner but is acting on the FB user's behalf, to request access to resources controlled by the FB user and hosted by the FB server.
Instead of using the FB user credentials to access protected resources, the web application obtains an access token.
Web application should be registered by Facebook to have an application ID (client_id) and secret (client_secret).
When request to some protected Facebook resources is received, web browser ("user agent") is redirected to Facebook's authorization server with application ID and the URL the user should be redirected back to after the authorization process.
User receives back Request for Permission form.
If the user authorizes the application to get his/her data, Facebook authorization server redirects back to the URI that was specified before together with authorization code ("verification string").
The authorization code can be exchanged by web application for an OAuth access token.
If web application obtains the access token for a FB user, it can perform authorized requests on behalf of that FB user by including the access token in the Facebook Graph API requests.
If the user did not authorize web application, Facebook issues redirect request to the URI specified before, and adds the error_reason parameter to notify the web application that authorization request was denied.

52. Examples … source: www.uml-diagrams.org
more examples at
Online Bookshop
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53. Examples for discussion Collaboration „Rent item”. source: www
Examples for discussion Collaboration „Rent item” source:
this example is just to show that there is another tool – only for sequence diagrams: trace modeler