Sequence Diagrams

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UML sequence diagrams sequence diagram: an "interaction

diagram" that models a single scenario executing in the system perhaps 2nd most used UML diagram (behind

class diagram)

relation of UML diagrams to other exercises: use cases -> sequence diagrams

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Key parts of a sequence diag.

participant: an object or entity that acts in the sequence diagram sequence diagram starts with an unattached

"found message" arrow

message: communication between participant objects

the axes in a sequence diagram: horizontal: which object/participant is acting vertical: time (down -> forward in time)

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Sequence diag. from use case

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Representing objects squares with object type, optionally

preceded by object name and colon write object's name if it clarifies the diagram object's "life line" represented by dashed

vert. line

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message (method call) indicated by horizontal arrow to other object write message name and arguments above arrow

dashed arrow back indicates return different arrowheads for normal / concurrent

(asynchronous) methods

Messages between objects

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Lifetime of objects creation: arrow with

'new' written above it notice that an object

created after the start of the scenario appears lower than the others

deletion: an X at bottom of object's lifeline Java doesn't explicitly

delete objects; they fall out of scope and are garbage-collected

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Indicating method calls activation: thick box over object's life

line; drawn when object's method is on the stack either that object is running its code, or it is

on the stack waiting for another object's method to finish

nest to indicate recursionActivation

Nesting

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Indicating selection and loops

frame: box around part of a sequence diagram to indicate selection or loop if -> (opt) [condition] if/else -> (alt) [condition], separated by horiz. dashed

line loop -> (loop) [condition or items to loop over]

[balance <> 0]opt [balance < 100.00]

[balance >= 100.00]

alt

[balance < 0]loop

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linking sequence diagrams if one sequence diagram is too large or refers to

another diagram, indicate it with either: an unfinished arrow and comment a "ref" frame that names the other diagram when would this occur in our system?

Verify customer credit

refCustomer Info

Approved?

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Example sequence diagram

sd Example

loop

StoreFront Cart Inventory

AddItemReserveItem

PlaceItemInOrder

Checkout

ProcessOrderConfirmOrder

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Flawed sequence diagram 1

What's wrong with this sequence diagram? (Look at the UML syntax and the viability of the scenario.)

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Flawed sequence diagram 2

What's wrong with this sequence diagram?

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Flawed sequence diagram 3

What's wrong with this sequence diagram?

:Computer :PrintServer :Printer :Queue

print(file)[if printer free] print(file)

[else] enqueue(file)

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Why not just code it? Sequence diagrams can be somewhat

close to the code level. So why not just code up that algorithm rather than drawing it as a sequence diagram? a good sequence diagram is still a bit above the level

of the real code (not EVERY line of code is drawn on diagram)

sequence diagrams are language-agnostic (can be implemented in many different languages

non-coders can do sequence diagrams easier to do sequence diagrams as a team can see many objects/classes at a time on same

page (visual bandwidth)

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Sequence diagram exercise 1

Let's do a sequence diagram for the following casual use case, Start New Poker Round :

The scenario begins when the player chooses to start a new round in the UI. The UI asks whether any new players want to join the round; if so, the new players are added using the UI.

All players' hands are emptied into the deck, which is then shuffled. The player left of the dealer supplies an ante bet of the proper amount. Next each player is dealt a hand of two cards from the deck in a round-robin fashion; one card to each player, then the second card.

If the player left of the dealer doesn't have enough money to ante, he/she is removed from the game, and the next player supplies the ante. If that player also cannot afford the ante, this cycle continues until such a player is found or all players are removed.

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Sequence diagram exercise 2

Let's do a sequence diagram for the following casual use case, Add Calendar Appointment :

The scenario begins when the user chooses to add a new appointment in the UI. The UI notices which part of the calendar is active and pops up an Add Appointment window for that date and time.

The user enters the necessary information about the appointment's name, location, start and end times. The UI will prevent the user from entering an appointment that has invalid information, such as an empty name or negative duration. The calendar records the new appointment in the user's list of appointments. Any reminder selected by the user is added to the list of reminders.

If the user already has an appointment at that time, the user is shown a warning message and asked to choose an available time or replace the previous appointment. If the user enters an appointment with the same name and duration as an existing group meeting, the calendar asks the user whether he/she intended to join that group meeting instead. If so, the user is added to that group meeting's list of participants.

Data Flow Diagrams

Where do they fit in?

Analysis (What do we do?) Fact finding

investigate business process and the current system

modelling the current and required systems

deliverables - requirements specification logical models of the

required system

Life Cycle Phases Planning Feasibility Study Analysis Design Code and Unit

test

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Data Flow Diagrams (DFD)

DFDs describe the flow of data or information into and out of a system what does the system do to the data?

A DFD is a graphic representation of the flow of data or information through a system

4 Main Elements

external entity - people or organisations that send data into the system or receive data from the system

process - models what happens to the data i.e. transforms incoming data into outgoing data

data store - represents permanent data that is used by the system

data flow - models the actual flow of the data between the other elements

Notation

Process box

D Data Store

ExternalEntity

Data Flow

• Data Flow

• Process

• External Entity

• Data Store

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Levelled DFDs

Even a small system could have many processes and data flows and DFD could be large and messy use levelled DFDs - view system at different

levels of detail one overview and many progressively greater

detailed views

Level 0 - Context Diagram

models system as one process box which represents scope of the system

identifies external entities and related inputs and outputs

Additional notation - system box

System boxExternalentity

Data flow out

Data flow in

Level 1 - overview diagram

gives overview of full system identifies major processes and data flows

between them identifies data stores that are used by the

major processes boundary of level 1 is the context

diagram

Level 2 - detailed diagram

level 1 process is expanded into more detail

each process in level 1 is decomposed to show its constituent processes

boundary of level 2 is the level 1 process

Other Notation

Duplicates marked by diagonal line in corner

System Boundary Elementary Processes - star in

corner Process that is levelled - dots on top

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Rules for DFDs

Numbering

Labelling

Balancing

Numbering

On level 1 processes are numbered 1,2,3…

On level 2 processes are numbered x.1, x.2, x.3… where x is the number of the parent level 1 process

Number is used to uniquely identify process not to represent any order of processing

Data store numbers usually D1, D2, D3...

Labelling Process label - short description of

what the process does, e.G. Price order Data flow label - noun representing the

data flowing through it e.G. Customer payment

Data store label - describes the type of data stored

Make labels as meaningful as possible

Balancing and data stores

Balancing any data flows entering or leaving a

parent level must by equivalent to those on the child level

Data stores data stores that are local to a process

need not be included until the process is expanded

Data Flows

Allowed to combine several data flows from lower level diagrams at a higher level under one data flow to reduce clutter

Flows should be labelled except when data to or from a data store consists of all items in the data store

Joe’s YardJoe’s builders’ suppliers has a shop and a yard. His system is

entirely manual. He has a stock list on the wall of his shop, complete with prices. When a builder wants to buy supplies, he goes into the shop and picks the stock items from the list. He writes his order on a duplicate docket and pays Joe, who stamps the docket as paid. The builder takes the duplicate docket and he goes to the yard and hands it to the yard foreman. The yard foreman gets the ordered items from the yard and gives them to the builder. The builder signs the duplicate docket and leaves one copy with the foreman and takes one copy as a receipt. Every week, Joe looks around the yard to see if any of his stock is running low. He rings up the relevant suppliers and reorders stock. He records the order in his order book, which is kept in the yard. The yard foreman takes delivery of the new stock and checks it against what has been ordered. He pays for it on delivery and staples the receipt into the order book. At the end of every month, Joe goes through all the dockets and the order book and produces a financial report for the shareholders.

Draw a context level DFD and a level-1 DFD for this system.

Context Diagram

Find the people who send data into the system Often data is part of a PHYSICAL transaction When handing a bar of chocolate to a

shopkeeper, you are handing him/her a barcode. Find the people who get data out of the

system. The only data you need is data that is

transformed or sent completely out of the system – not data that is handled by an operator within the system.

Joe’s YardJoe’s builders’ suppliers has a shop and a yard. His system is

entirely manual. He has a stock list on the wall of his shop, complete with prices. When a builder wants to buy supplies, he goes into the shop and picks the stock items from the list. He writes his order on a duplicate docket and pays Joe, who stamps the docket as paid. The builder takes the duplicate docket and he goes to the yard and hands it to the yard foreman. The yard foreman gets the ordered items from the yard and gives them to the builder. The builder signs the duplicate docket and leaves one copy with the foreman and takes one copy as a receipt. Every week, Joe looks around the yard to see if any of his stock is running low. He rings up the relevant suppliers and reorders stock. He records the order in his order book, which is kept in the yard. The yard foreman takes delivery of the new stock and checks it against what has been ordered. He pays for it on delivery and staples the receipt into the order book. At the end of every month, Joe goes through all the dockets and the order book and produces a financial report for the shareholders.

Draw a context level DFD and a level-1 DFD for this system.

Context diagram

Joe'sYard

Joe Customer

Supplier

Shareholders

Docket &Payment

Signed docket

Supply needs

Supply invoiceSupply order& payment

financialreport

Level-1 DFD processesJoe’s builders’ suppliers has a shop and a yard. His system is

entirely manual. He has a stock list on the wall of his shop, complete with prices. When a builder wants to buy supplies, he goes into the shop and picks the stock items from the list. He writes his order on a duplicate docket and pays Joe, who stamps the docket as paid. The builder takes the duplicate docket and he goes to the yard and hands it to the yard foreman. The yard foreman gets the ordered items from the yard and gives them to the builder. The builder signs the duplicate docket and leaves one copy with the foreman and takes one copy as a receipt. Every week, Joe looks around the yard to see if any of his stock is running low. He rings up the relevant suppliers and reorders stock. He records the order in his order book, which is kept in the yard. The yard foreman takes delivery of the new stock and checks it against what has been ordered. He pays for it on delivery and staples the receipt into the order book. At the end of every month, Joe goes through all the dockets and the order book and produces a financial report for the shareholders.

Verbs from script Has (passive) Buy supplies Picks stock items Writes order Pays joe Stamps docket Takes docket to yard Hands it to foreman Gets items Gives them to builder

Builder signs docket Takes copy as receipt Looks around yard and

reorders Records order in order

book Foreman takes delivery –

checks Foreman pays supplier Staples receipt to order

book Produces financial report

Remove passive verbs and queries

Passive: has stock list Buy supplies

Picks stock items (views list)

Writes orders Pays joe Stamps docket

Customer then Takes docket to yard Hands it to foreman

Gets items Gives them to builder Builder signs docket Takes copy as receipt

Joe then Looks around yard and

reorders Records order in order book

Foreman takes delivery – checks Foreman pays supplier Staples receipt to order book

Joe Produces financial report

Level 1 current physical

Customer

Buysupplies

20

getitems

12

Reordersupplies

21

Restock

22

*

Producefinancialreport

Joe's Office5

Joe

Orderbook

M3

DocketM1

Money

stock

Shareholders

Supplier

Foreman

*

Taketo

yard

11Supply needs

financialreport

Docket &Payment

Supply order

Docket

Signed docket

Signed docket

Signed docket

Payment

required stock

required stock

completeddocket copy

completeddocket copy

Supply order

supplies

supplies

Payment Payment

Supplierreceipt

Supplierreceipt

completeddocket copy

buildersignature

Buy Supplies

Buy supplies20 DocketM1

Money

Customer

*

WritesOrder

20.1

*

PaysJoe

20.2*

StampDocket(signatu-

re)

20.3

Docket

Payment

Docket

Payment Docket

Get Items

get items12

Foreman

stock

*

Give itemsto customer

12.1*

Get buildersignature

12.2

*

Givecopy

as receipt

12.3

Customer

Signed docket

required stock

buildersignature

Signed docket

completeddocket copy completed

docket copy

Reorder supplies

Reorder supplies21

OrderbookM3

Joe

*

Reorderfromyard

21.1

*

Recordorder

21.2

Supply order

Supply needs

Supply needs

Restock

Restock22

stock

Orderbook

M3

Supplier

Money

*

Takedelivery

22.1

*

Paysupplier

22.2

supplies

Payment

Supplierreceipt

Supply order

supplies

Payment

Supply order