Lecture 10 Object-Oriented Analysis (System Sequence Diagrams by ias80075

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									ECE 452- Introduction to Software Engineering

Lecture 10: Object-Oriented Analysis
    (System Sequence Diagrams,
         Conceptual Model)

        Manish Parashar
    parashar@ece.rutgers.edu
    Department of Electrical &
      Computer Engineering
       Rutgers University
The Unified Analysis Process & UML
♦   Use Case - What are the domain processes ?
    − Use Case Diagram
       ♦   high-level/expanded, essential/real
♦   Conceptual Model - What are the domain concepts, terms ?
    − Class Diagram (conceptual)
       ♦   classes, associations, attributes
♦   System Sequence Diagram - What are the system events
    and operations ?
    − Interaction Diagram - Sequence Diagram
♦   Contracts - What do the system operations do ?
    − Contract Specs.


                          ECE 452 - Introduction to Software Engineering
                 Sample UP Artifacts                                                   Partial artifacts,
                                                 Domain                                refined in each
   Business                                       Model                                    iteration.
   Modeling

                                                                                             parameter or
                                                                                             return data may be
                                                                                             elaborated in the
                                                                                             Glossary
               Use-Case Model


                                                          :System

                                               foo( x )
Requirements                                                                                    Glossary    ...
                                               bar( y )
                          system                                    system
                  text    events &          system                  operations
                                                                                  system
                  use     data             sequence                              operation
                 cases                     diagrams                              contracts



                                                                                Software
                                Design Model               design objects
                                                                            Architecture Doc.
                                                           to handle the
     Design                                                system events




                                      Software
                                     Dev. Plan
     Project
 Management


                 Test
                 Plan                                                                        Development
                                                                                                Case
        Test                                                           Environment

               ECE 452 - Introduction to Software Engineering
From Analysis to Design

♦ Use   Cases
  − What are the domain processes ?
♦ Conceptual     Model
  − What are the concepts, terms ?
♦ System   sequence diagrams
  − What are the system events and operations ?
♦ Contracts
  − What do the system operations do ?


                ECE 452 - Introduction to Software Engineering
System Sequence Diagrams

♦ Determine  system events and operations
♦ Derived from Use Cases – Typical course of
  events
♦ Identify system functionality (operations) to
  be designed
♦ System boundary is critical




              ECE 452 - Introduction to Software Engineering
System Sequence Diagrams

          events from actors to systems
♦ Illustrate
♦ System sequence diagrams describe scenarios
   − a scenario is an instance of a use case Ivar Jacobson
   − a real example of the enactment of a use case
   − e.g. Process Sale
♦ Some UML notation for a sequence diagram is
  shown on the next slide


                ECE 452 - Introduction to Software Engineering
System Sequence Diagrams

♦ Draw   a line representing the system as a black
  box.
♦ Identify each actor that directly operates on
  the system. Draw a line for each such actor.
♦ From expanded use case identify system
  events that each actor generates. Ilustrate
  them.
♦ Optionally include use case text on left.


              ECE 452 - Introduction to Software Engineering
A System Sequence Diagram
                                                                                   system as black box


                                                 Buy Items-version 1
        Actor


                                    Cashier                                      :System




                  Repeat until no               enterItem(UPC, quantity)
                   more items


                                                        endSale()

Text which clarifies
control, logic, iteration,
                                                 makePayment(amount)
etc.

May be taken from the
use case.
                                              system event

                                              it triggers a system operation


                                ECE 452 - Introduction to Software Engineering
System events
♦   System Event
    − An external input event generated by an actor to a system
    − the system is seen as a black box
♦   System operation
    − the method invoked in response to a system event
♦   Use the same names for system event and system
    operation
♦   System events may have arguments
       ♦   enterItem( UPC, quantity )
       ♦   raise( money )

                     ECE 452 - Introduction to Software Engineering
System Sequence Diagrams from Use Cases

                                              : Cashier                                :System

                                                                    makeNewSale(
Simple cash-only Process Sale scenario:                                  )

1. Customer arrives at a POS checkout                              enterItem(itemID,
with goods and/or services to purchase.                                quantity)
2. Cashier starts a new sale.
3. Cashier enters item identifier.                                    description,
4. System records sale line item and                                     total
presents item description, price, and                               * [more items]
running total.
Cashier repeats steps 3-4 until indicates
done.                                                                  endSale(
5. System presents total with taxes                                       )
calculated.
6. Cashier tells Customer the total, and                              total with
asks for payment.                                                       taxes
7. Customer pays and System handles
payment.                                                        makePayment(amount
...                                                                     )

                                                                     change due,
                                                                       receipt
                                 ECE 452 - Introduction to Software Engineering
Naming System Events and Operations



                                                                   :System
                         : Cashier
   better name
                                     enterItem(itemID, quantity)



                                       scan(itemID, quantity)

   worse name




                 ECE 452 - Introduction to Software Engineering
SSD with Use Case Text
 Simple cash-only Process Sale scenario:

 1. Customer arrives at a POS checkout                                              :System
 with goods and/or services to purchase.     : Cashier
 2. Cashier starts a new sale.                                   makeNewSale(
                                                                      )


 3. Cashier enters item identifier.                             enterItem(itemID,
 4. System records sale line item and                               quantity)
 presents item description, price, and
 running total.                                                    description,
                                                                      total
                                                                 * [more items]


 Cashier repeats steps 3-4 until indicates                          endSale(
 done.                                                                 )
 5. System presents total with taxes                               total with
 calculated.                                                         taxes

 6. Cashier tells Customer the total, and
 asks for payment.                                            makePayment(amount
 7. Customer pays and System handles                                  )
 payment.
 ...
                                                                  change due,
                                                                    receipt
                               ECE 452 - Introduction to Software Engineering
System Behavior - Contracts
♦ Contracts help define system behavior
♦ Contracts are defined in part by preconditions
  and postconditions
♦ Examples in this chapter document system
  operations such as
    − enterItem
    − endSale
    − makePayment
♦   However, contracts also apply to low-level methods
                ECE 452 - Introduction to Software Engineering
The Conceptual Model- Introduction

♦ Conceptual      Model
  − illustrates meaningful concepts
  − most important artifact in OO analysis
  − need use cases as input
     ♦   but can develop uses cases as you do conceptual model
♦ Question:
  − Provide names for the uses cases you found
     ♦   let's share this information now (use whiteboard)


                 ECE 452 - Introduction to Software Engineering
Domain Analysis

♦ Object   oriented analysis at the “business area
  level”
♦ Objective: Create a library of reusable
  components for a particular domain
♦ Ongoing activity of the software process (not
  tied to a specific project)
♦ Domain analysis model specifies objects and
  classes that characterize the domain


               ECE 452 - Introduction to Software Engineering
Domain Analysis

♦ Define  domain to be investigated
♦ Categorize the items extracted from the
  domain
♦ Collect a representative sample of applications
  in the domain
♦ Analyze each application in the sample
♦ Develop an analysis model for the objects
♦ Define reuse guidelines


             ECE 452 - Introduction to Software Engineering
Conceptual Models

♦ Conceptual       Model
  − created for the use cases of the current cycle in the
    language of the problem domain
♦ Must    identify
  − concepts - objects in our system
  − associations between concepts
     ♦   is part of, contains, manages, is-a, ...
  − attributes of concepts
     ♦   instance variables needed to hold state
                  ECE 452 - Introduction to Software Engineering
Conceptual Modeling...

♦ Conceptual    models should not contain design
  information
  − software artifacts, methods, etc.
       to over specify then under specify
♦ Better
♦ Concepts v/s attributes
  − when in doubt make it a concept
♦ Specification/Description                concepts


              ECE 452 - Introduction to Software Engineering
Conceptual Modeling

♦ Associations
  − less important than identifying concepts
  − show only “need-to-know” association (avoid
    redundant or derivable associations)
  − name, multiplicity, navigability
  − multiple associations




             ECE 452 - Introduction to Software Engineering
Conceptual Model

♦ Attributes
  − Attributes Vs. Concepts
     ♦   keep attributes simple
     ♦   if in doubt define it as a concept
     ♦   no attributes as foreign keys (use associations)




                 ECE 452 - Introduction to Software Engineering
A Partial Conceptual Model

♦ See   example for POST on page 88 also on next slide
  − Figure 9.1
     ♦   shows attributes name some instance variables now ________
     ♦   shows associations name a label now
     ♦   contains multiplicity
           • numbers at the ends of the association lines
               – 1, 0..1, 1..4 (one to four players), * means many
           • direction reading arrow which could be left-to-right and top-
             to-bottom by default (but this is not a standard rule)
           • Arrows help readability
     ♦   typically can read the multiplicity both ways
♦ More    on associations and multiplicity later
                   ECE 452 - Introduction to Software Engineering
Concept                            Sales
                                                                                Item
                                 LineItem            Records-sale-of
                                              0..1                     1
                          quantity

                                      1.. *                                              *
                                                                       Stocked-in
Association           Contained-in

                                       1                                                 1

                                  Sale                                          Store

Attributes                date                                             address
                          time                1                            name
                                                                                         1
                                  1
                                                                                        Houses
 We're shooting
                          Paid-by                                                       1.. *
 for something
 like this for your               1                                             POST
                                                       Captured-on 4
 final project                   Payment
                                                                       1
                          amount
                          ECE 452 - Introduction to Software Engineering
Conceptual Model

♦ Conceptshelp with domain vocabulary
♦ Conceptual models are not models of software
  designs
  − don’t be thinking windows and files here
  − no responsibilities yet, do this in design
♦ Concept:   an idea, thing, or object
  − symbol: a word or image representing a concept
  − definition
  − extension: set of examples to which the concept applies
              ECE 452 - Introduction to Software Engineering
Example Concept

♦ POST    Sale                                   Sale            concept's symbol

                                       date
  − symbol: Sale                       time


  − definition
    represents the event         "A sale represents the event    concept's definition
                                 of a purchase transaction. It
    of a purchase                has a date and time."

    transaction, and has
    a date and time
  − extension: the set                sale-1


                                                        sale-2   concept's extension
    of all sales                     sale-3



                                               sale-4




               ECE 452 - Introduction to Software Engineering
Example Concept

♦ POKER     Card                      CardDeck                  concept's symbol

                                      rank
  − symbol: Card                      suit


  − definition:
    represents one card         A card represents one of the
                                entities to make up a hand      concept's definition
    in a poker deck that         in a poker game

    has a rank (2..14),
    and a suit ♣♦♥♠
  − extension: the set               Ace ♥


                                                                concept's extension
    of all cards                     3♣
                                                   King ♦


                                             5♠




               ECE 452 - Introduction to Software Engineering
Conceptual model and partitioning

♦ Structured     Analysis (still in use today)
  − Divide and Conquer
     ♦   at the function level
♦ Object-Oriented            Analysis (still growing)
  − Partition
     ♦   at the level of concepts (objects)




                  ECE 452 - Introduction to Software Engineering
Identifying Concepts

♦ One    strategy for getting concepts
  − Look for the concepts in the problem specification
    and in your uses cases
     ♦   read the final project specification
  − It is better to have too many at first than too few
     ♦   specifying too many concepts is good
     ♦   is is better too have too many than too few
     ♦   concepts may have no attributes
♦ Try   not to think of Java classes as you do this
  − later on, think of some classes to implement
                  ECE 452 - Introduction to Software Engineering
Concept Category

♦ Physical   or tangible things
  − POST A Point of Sale Terminal
♦ Specifications
  − POST ProductDescription
♦ Transactions
  − POST Sale, Payment




               ECE 452 - Introduction to Software Engineering
More Concept Categories

♦ Things   in a container
  − POST Sales Line Item
♦ Abstract   noun concepts
  − POST Waiting line rage
♦ Events
  − POST Sale




               ECE 452 - Introduction to Software Engineering
More Concept Categories

♦ Rules   and Policies
  − POST RefundPolicy
♦ Organizations
  − POST SalesDepartment

            For more, see pages 91-93




              ECE 452 - Introduction to Software Engineering
Concepts?                page 96-97

♦ Use vocabulary of the users
  − Users are not usually present for college programming
    projects
  − However, Poker has users
       ♦   the users are you this isn't a Library with Patrons and Librarians

♦ Do   not include irrelevant things
   − no casino, no pit boss
♦ Do not include things that don't belong
  − no Lottery System, no Starship Enterprise, no pit bull

                      ECE 452 - Introduction to Software Engineering
Finding Concepts

♦ Make    a list of candidate concepts (objects)
  − look for noun phrases
     ♦   be careful to avoid ambiguities
     ♦   see page 95 POST Item, Store, Sale, Payment, Customer




                 ECE 452 - Introduction to Software Engineering
Common Mistake
♦   Do not mistake an attribute for a concept
    − Attributes are numbers, booleans, strings, date
♦   All others things are likely a concept
    − if in doubt, make it a concept
♦   Example: Payment in the POST problem could be
    thought of as the amount of a Sale
    − a primitive attribute like 9.75
    − But a payment could be made by check, cash, credit card,
      could be in various currencies of the world, could require
      change
    − This outgrows being a simple attribute


                  ECE 452 - Introduction to Software Engineering
Resolving Similar Concepts

♦ Naming     things correctly is
                                                       similar concepts with
  − important                                          different names
  − sometimes hard to agree:

        POST                     or?                      Register

             1                                                    1
 Records 6                                     Records6


             *                                                    *
         Sale                                               Sale

                 ECE 452 - Introduction to Software Engineering
Abstract Concepts
♦   Some concepts don't feel real                 and that is okay
    − Telecommunications
       ♦   Connection, Route, Protocol
    − Poker
       ♦   Strategy, View
    − Encoding images with some compression scheme or
      encrypting messages for privacy
       ♦   Compression, Encryption, Privacy
♦   Concepts in the problem domain exist even if they do
    not seem to be part of the real world


                    ECE 452 - Introduction to Software Engineering
                                 Credit                 Credit        Check
                                                                     Approval
POST Concepts                 Authorization
                                Service
                                                       Approval
                                                       Request       Request


                                 Check                  Credit        Check
 Accounts    Drivers          Authorization            Approval      Approval
Receivable   License            Service                 Reply         Reply



  Cash        Credit              Check                   Credit
                                                                      Check
 Payment     Payment             Payment                  Card




                                                                     Product
  POST        Item                 Store                   Sale
                                                                     Catalog


   Sales                                                             Product
             Cashier              Customer               Manager
 LineItem
                                                                   Specification
                 ECE 452 - Introduction to Software Engineering
Defining Terms in the UML
♦   The Software class diagram will look a lot like the
    conceptual model
♦   You will see associations, boxes, multiplicity...
♦   Larman uses concept to refer to real world things and
    unreal things
♦   Classes refer to software specifications and
    implementations. UML defines class as
     − a description of a set of a objects that share the same
       attributes, relationships, and semantics
          the three Amigos: Grady Booch, Ivar Jacobsen, Jim Rumbaugh




                      ECE 452 - Introduction to Software Engineering
Other UML terms

♦ Operation
  − a service that can be requested from an object to
    affect behavior
♦ Type
  − either a class or an interface specification with no methods
♦ Interface
  − the set of externally visible operations
     ♦   Could mean a Java interface



                 ECE 452 - Introduction to Software Engineering
Adding Associations

♦ Next   step in the conceptual model
  − adding associations between two concepts
  − an association is
     ♦   a relationship between concepts that indicates some
         meaningful and interesting connection
  − Name the association with a hyphen connected
    verb phrase which reads well between concepts
                                             association




                           Records-current
           POST                                            Sale
                       1                      1
                  ECE 452 - Introduction to Software Engineering
Associations

♦ Associations       imply
  − our knowledge of the relationship must be
    preserved for some time (1 ms to forever)
     ♦   between what objects do we need to remember a
         relationship?
          • POST: does a driver's license remember a product catalog?
          • Poker: does a game need to remember it's Player(s)?
          • Poker: does the winner need to know the card image
            collection?




                 ECE 452 - Introduction to Software Engineering
The UML Association Notation
♦ UML   Association:
  − a line between two concepts and a name
  − they are bi-directional    *   T
                                        zero or more;
                                        "many"
  − can have a multiplicity
  − exist in conceptual         *
                              1..
                                   T    one or more

      models and
                            1..40
      class diagrams               T    one to forty



                                           5
                                                    T          exactly five
         Multiplicity
         adornments
                                       3, 5, 8                 exactly three,
                                                    T
                                                               five or eight
              ECE 452 - Introduction to Software Engineering
Possible Associations
♦   A is a physical part of B Drawer - POST
♦   A is a logical part of B SalesLineItem - Sale
♦   A is physically contained in B POST-Store
♦   A is logically contained in B ItemDescription-Catalog
♦   A is recorded in B Sale - POST
♦   A uses or manages B Cashier - POST
♦   A communicates with B Customer - Cashier
♦   A is related to a transaction B Customer - Payment
    − Draw some poker associations now
        ♦   Let's try to get one for each of the bullets above
                     ECE 452 - Introduction to Software Engineering
Associations

♦ Some   useful associations
  − A is a physical or logical part of B
  − A is physically or logically contained in/on B
  − A is recorded in B




              ECE 452 - Introduction to Software Engineering
Association Guidelines

♦ Concepts are more important than associations
♦ Focus on need to know associations
  − the relationship must be preserved for some time
♦ Better   to have too few associations than too
  many




               ECE 452 - Introduction to Software Engineering
Multiplicity

♦ Multiplicitydefines how many instances of
  type A can be associated with one instance of
  type B at some point can differ
    Game                                            Player
              1                          1..6


    Mother                                           Child
              1                           1+

                      performs-in                                  Actor is associated
     Actor                                            Film         with 0 to many films.
              *                            *                       A film is associated
             can optionally name an association                    with 0 to many actors
                  ECE 452 - Introduction to Software Engineering
Depends on Context

♦ Are   all three associations possible?

        Car                                        Wheel
                1                        4


        Car                                        Wheel
                1                        5


        Car                                        Wheel
                1                        3




               ECE 452 - Introduction to Software Engineering
Association Names                         Upcase / hyphenate

♦   Try reading this      Type-VerbPhrase-Type


         Store
            1
           Contains

              *
            1..

        POST        Captures            Sale             Paid-by       Payment
                  1          *
                           1..                      1              1

♦   Not yet worrying about messages, instance variables,
    data flow, or software objects
♦   Just show some concepts are connected
                  ECE 452 - Introduction to Software Engineering
No Implementation Yet

♦ Theassociations may later become
 implemented in software in terms of visibility
  − Related as an instance variable of a class
  − Related as an argument in a message
  − Related through an inheritance relationship
♦ Some   associations will not be implemented
  − Others will be discovered during coding
♦ ConceptualModel should have associations
 suggested by requirements and use cases
              ECE 452 - Introduction to Software Engineering
Any unforgettable Relationships?

♦ POST
  − Post Captures Sale
  − Sale Paid-By Payment
  − ProductCatalog Records Specification




             ECE 452 - Introduction to Software Engineering
  Conceptual Model for the POST associations are not all need to know
                             Records-sale-of

                                                                Described-by                                            1

                                                                                                                 Product
                                                                  Product                                      Specification
                                                                  Catalog               Contains
                                                                                    1                1.. *

                                                                    1
             0..1                                                             Used-by
                               *                                                                                            Describes
                  Sales                                                       *                                        *
                LineItem                                            Store
                                                                                                                    Item
                                                                                         Stocks
                                                        1                           1                                              1
                                                                                                      *
                            1.. *
                                                     Logs-              1
      Contained-in                                                            Houses
                                                   completed
                         1                             6                    1.. *

                     Sale             *                            POST
                                                                                                               Manager
                                          Captured-on                                   Started-by
                                      1                 1                           1                  1
                                      1
                                1
                     1              Initiated-by                    1
      Paid-by                                                            3 Records-sales-on
  1                                           1                                                            1                   see pages
                                                               Initiated-by
Payment                               Customer                                                    Cashier                      116-117
                                                                                         1

                                             ECE 452 - Introduction to Software Engineering
       Not need to know                 No need yet to have POST Started-By Manager
                                                                   Records-sale-of

                                                                Described-by                                         1

                                                                                                              Product
                                                                  Product                                   Specification
                                                                  Catalog               Contains
                                                                                    1              1.. *

                                                                    1
             0..1                                                             Used-by
                               *                                                                                         Describes
                  Sales                                                       *                                     *
                LineItem                                            Store
                                                                                                                 Item
                                                                                         Stocks
                                                        1                           1                                           1
                                                                                                    *
                            1.. *
                                                     Logs-              1
      Contained-in                                                            Houses
                                                   completed
                         1                             6                    1.. *

                     Sale             *                            POST
                                          Captured-on
                                      1                 1
                                      1
                                1
                     1              Initiated-by                    1
      Paid-by                                                            3 Records-sales-on
  1                                           1                                                         1                   see pages
                                                               Initiated-by
Payment                               Customer                                                    Cashier                   116-117
                                                                                        1

                                             ECE 452 - Introduction to Software Engineering
                         Not need to know               No one said Store Stocks Items
                                                                   Records-sale-of

                                                                Described-by                                        1

                                                                                                             Product
                                                                  Product                                  Specification
                                                                  Catalog               Contains
                                                                                    1              1.. *

                                                                    1
             0..1                                                             Used-by
                               *                                                                                        Describes
                  Sales                                                       *                                    *
                LineItem                                            Store
                                                                                                                Item
                                                         1                                                                     1

                            1.. *
                                                     Logs-              1
      Contained-in                                                            Houses
                                                   completed
                         1                             6                    1.. *

                     Sale             *                            POST
                                          Captured-on
                                      1                  1
                                      1
                                1
                     1              Initiated-by                    1
      Paid-by                                                            3 Records-sales-on
  1                                           1                                                        1                   see pages
                                                               Initiated-by
Payment                               Customer                                                 Cashier                     116-117
                                                                                        1

                                             ECE 452 - Introduction to Software Engineering
Need to Know vs. Comprehension
♦   Could do a strict need-to-know model
    − bounded by current requirements only
    − but it may not convey a full understanding
♦   By eliminating concepts and associations that are not
    currently required need to know
    − the conceptual model may not communicate key ideas and
      relationships
♦   Make your conceptual model so it
    − has need to know requirements what the system must do
    − clearly communicates important concepts
        ♦   could have View as a concept



                     ECE 452 - Introduction to Software Engineering
Summary

♦ Doubting    whether to keep a concept?
  − keep it
♦ Doubting    whether to keep an association?
  − drop it
♦ Do   not keep derived associations
  − Where A relates to B and B relates to C usually
    leave out the A to C relationship
♦ Does model satisfy all need to know associat-
 ions and still present a clear complete picture?
               ECE 452 - Introduction to Software Engineering
Identifying Attributes

♦ The  final piece to the conceptual model is to
  add the attributes needed to support use cases
♦ Attribute: a logical data value of an object
  − not necessarily in the final design, though some
    attributes will end up in the code
♦ Example:  A bank customer has an account ID
  and a balance
  − both could be attributes in the conceptual model
  − both could be instance variables in a class diagram
              ECE 452 - Introduction to Software Engineering
Keep attributes simple
♦ Look   for simple data types as attributes
  − boolean, date, number, string                  like data base primitives

♦ Do not use complex ideas as attributes
♦ UML puts attributes in 2nd row of concept
  box
                 Sale
                                                      attributes
          date
          startTime : Time




                ECE 452 - Introduction to Software Engineering
Attribute or Association?

♦ Easy     to mistake a concept as an attribute
                    Cashier
  Worse                                             not a "simple" attribute
             name
             currentPOST




                    Cashier                                          POST
  Better                               1     Uses       1
             name                                           number


                 ECE 452 - Introduction to Software Engineering
Attribute or Association?

♦ Attributes should be simple, if complex, write
  it as a concept with an association
               Flight                               destination is a complex
   Worse                                            concept
            destination




                Flight      1      Flies-to     1       Airport
   Better




                 ECE 452 - Introduction to Software Engineering

								
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