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Modeling System RequirementsEvents and Things

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									         Modeling System Requirements:Events and
                                 Models and modeling
                            Events and system requirements
                            Things and system requirements
                            The entity-Relationship Diagram
                                  The Class Diagram

Management information system          5_ 1                   Huang Hong
        Models and modeling
             The purpose of models
             Types of models
        Events and system requirements
               Events
               Types of events (external event, state event, temporal event时序事件)
               System controls
               Perfect technology assumption
               Event table, how to develop an event table*
        Things and system requirements
               Types of things
               Relationship among things (cardinality or multiplicity)
               Attributes, compound attribute, key or identifier
               Data entity, class, methods, encapsulation
        The Entity-Relationship Diagram[实体联系图]
             ERD notations, how to develop ERD*
        The Class Diagram
             Class diagram notations, how to develop class diagram*

Management information system                  5_ 2                                 Huang Hong
          Waiters on wheels:
          computerized delivery tracking
        Waiters on Wheels is a restaurant meal-delivery service started in 1997
        Business expanding made the owner realized that they need a custom
         (定制的,专门的) computer system to support their operations
        Consultant Sam Wells help them to define the system they needed.
        The investigation process and the brief result.

        Notice how Sam found out their requirements

Management information system         5_ 3                               Huang Hong
                                 Models and Modeling
        Models
             A representation of some of the important aspect of the system being built
        modeling
             The process of creating models
        The purpose of models
             Models can be used to document the system analysis and design result
             Learning from the modeling process
             Reducing complexity by abstraction and helping focus the analyst’s efforts on a
              few aspects of the large, complex information at a time
             Models are used as memory aids for analysts
             Models are used as communication media between team members and
             Requirements models are used as documentation for future development teams
              when they maintain or enhance the system
        Types of models
             Mathematical model:a series of formulas that describe technical aspects of a system
             Descriptive model:narrative memos, reports, or lists that describe some aspect of a
             Graphical model:diagrams and schematic representations of some aspect of a

Management information system                5_ 4                                          Huang Hong
                  Overview of models used in analysis

Management information system   5_ 5                Huang Hong
                   Overview of models used in design

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                     Events and System Requirements
        All approaches of system development begin the modeling process
         with the concept of an event, events drive or trigger all processing that
         a system does, so it is a good idea to list and analyze the system’s
         events when you need to define system requirements
        Events:an occurrence at a specific time and place, that can be
         described and is worth remembering
        The event concept comes from the analysis of real time systems
        Types of events
             External event: an event that occurs outside the system, usually initiated
              by an external agent or actor
             Temporal event: an event that occurs as a result of reaching a point in time
             State event: an event that occurs when something happens inside the
              system that triggers the need for processing

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                  External events and temporal events
        Events
        The background of the event concept

Management information system         5_ 8          Huang Hong
                                  Identifying Events
        Guidelines for identifying events
             distinguishing an external event and conditions that leads up to the event,
              distinguishing an external event and system’s response
             tracking a transaction’s life cycle will help identifying events in sequence
             Ignoring technology-dependent events and system controls during analysis
              phase. ( e.g. logging on, database backup, change password etc.)
                 System control: checks or safety procedures put in place to protect the
                   integrity of the system
                 Perfect technology assumption: the assumption that events should be
                   included during analysis only if the system would be required to
                   respond under perfect conditions(equipment never breaking down,
                   capacity of processing and storage being unlimited, people operating
                   the system being completely honest and never making mistakes),
                   under this assumption, analysts can eliminate technology-dependent
                   events during analysis phase.

Management information system             5_ 9                                    Huang Hong
               Distinguishing Conditions versus events

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            Tracking transaction’s life cycle to identify

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          Events in the Rocky Mountain Outfitters Case
        External events for the RMO customer support system
               Customer wants to check item availability
               Customer places an order
               Customer changes or cancels order
               Customer or management wants to check order status
               Shipping fulfills order
               Shipping identifies back order
               Customer returns item(defective, changed mind, full or partial returns)
               Prospective customer request catalog
               Customer updates account information
               Marketing wants to send promotional materials to customers
               Management adjusts customer charges(correct errors,make concessions)
               Merchandising updates catalog(add, change,delete,change price)
               Merchandising creates special product promotion
               Merchandising creates new catalog

Management information system              5_ 12                                  Huang Hong
           Events in the Rocky Mountain Outfitters Case(cont)
        Temporal events for the RMO customer support system
                Time to produce order summary reports
                Time to produce transaction summary reports
                Time to produce fulfillment summary reports
                Time to produce prospective customer activity reports
                Time to produce customer adjustment/concession[让步] reports
                Time to produce catalog activity reports
        Look at each event: Event table
                                                                          What output(if any)is
                                                                          produced by the system

               Event              Trigger   Source         Activity           Response             Destination
          Customer want to          Item                  Look up item      Item availability
                                            customer                                                 customer
        check item availability   inquiry                  availability          details

          How does the system know the
          event occurred: external event: data
          entering the system; temporal event:
          time arrived

Management information system                     5_ 13                                              Huang Hong
                      Things and System Requirements
        To define system requirements involves understanding and modeling things
         that the system needs to store information about. In the object-oriented
         approach, these things are the objects that interact in the system.
        Types of Things
             Tangible things: such as products
             Intangible things: an order, a service call
        Relationship among Things
             Information about relationship among things are equally as important as
              information about things, such as an employee works at a specific department.
             Cardinality: the number of associations that occur between specific things. One to
              one; one to many; many to many
             Multiplicity: A synonym for cardinality, often used with the object-oriented
             N-ary relationship[N元联系]: A term to describe how many things’s relationship is
              the relationship used to represent. Binary relationship; unary (recursive)
              relationship; ternary relationship; n-ary relationship
        Attributes of Things: an attribute is one piece of specific information about a
             identifier (key)
             Compound attribute: address(city,street,apartment)
             Multi-value attribute:telephone number(another form of compound attribute)

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                                        Data Entities
       Data entities
            The things the system needs to store information about in the traditional
             approach to information systems
       ERD (entity-relationship diagram)
            A graphic modeling method used to describe data entities, the relation-
             ships between data entities, and the attributes of data entities and
            Cardinality symbols of relationships in ERD

               Exactly one (mandatory                        Zero or more (optional)

               Zero or one (optional)                        One or more (mandatory)

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                           The Entity-Relationship Diagram
                    Example of data entity
                                                     Cardinality symbols of relationships in ERD

     Entity name                Customer               Exactly one (mandatory)   Zero or more (optional)
                                Cust number*
    Key attribute                   Name
                                 Bill address
                                Home phone             Zero or one (optional)    One or more (mandatory)
      attributes                Office phone

                                                                                    A weak entity set

          Customer                                   Order                           Order item
          Cust number*
           Bill address                             Order ID*                           Item ID*
          Home phone                                Order date                          Quantity
          Office phone                               amount                               price

                                                Sample ERD

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                    The Entity-Relationship Diagram

                                                Many to many relationship often involve
                          Course                additional data that must be stored. Example:
                                                if a student select a course, he/she will get a
                       Course number*
                            title               Where to store the grade?
                        Credit hours

                      Course section                              student

                       section number*                           Student ID*
                          Start time                                Name
                        Room number                                 major

                            Sample ERD with many to many relationship

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                         The Entity-Relationship Diagram
                                 Associative entity
                                A data entity that represents a many to many relationship
                                   between two other data entities

       Course number*
        Credit hours

      Course section                         Course                            student
       section number*                                                        Student ID*
          Start time                                                             Name
        Room number                             grade                            major

                                Sample ERD with Associative entity

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             The Rocky Mountain Outfitters Case ERD

                       package                  Product item


                     Return item   Order item    shipment

                      Customer       Order

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                                 Objects and classes
        Objects
             A term used in object-oriented approach, similar to data entities in the
              traditional approach. The differences between them is that data entities
              only store information, the objects not only store information, but also do
              works, that is, they can process information themselves. objects have both
              attributes and behaviors.
        Class
             The type or classification to which all similar objects belong
             Methods: the behaviors all objects of the class are capable of.
             Encapsulation[封装]: covering or protecting each object so that it contains
              values for attributes and methods for operating on these attributes, making
              the object a self-contained [设备齐全的, 独立的]( and a protected) unit.

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                  More issues about classes of objects
           Generalization[一般化]/specialization[特殊化] hierarchies
               Hierarchies that structure or rank classes from the more general
                superclass to the the more specialized subclass
           Inheritance[继承]
               A concept that allows subclasses to share characteristics of their


                   Web Order            Telephone Order          Mail Order

Management information system             5_ 21                                      Huang Hong
             More issues about classes of objects (cont)
             Aggregation[聚集] ( whole-part hierarchies)
                A relationship between an object and its parts


                processor                                                    Monitor

                            Main memory                       Disk storage


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                                    The Class Diagram
        Class diagram
             In the object-oriented approach, we build class diagram to help understand
              things involved in a system. Because the class concept is different from
              data entities’s, the sets of requirements models for object-oriented
              approaches are quite different from the traditional approaches’s too.

        Examples of class diagram notation

                                                   The name of the class

                    Address           Attribute:all objects in the class have a value
                     Phone                           for each of these

                   Add new
                    Delete            Methods:what all objects of the class know
                   Change             how to do. Methods are not always shown in
               Connect to account      the class symbol if they are fairly standard.

Management information system              5_ 23                                        Huang Hong
                                    The Class Diagram
        Examples of class diagram notation (a bank account class diagram)

             Customer                                     Account

               Name        1            0..*         Account Number
              Address                                   Balance
               Phone                                  Date opened
                                                      Make Deposit
                                                     Make withdrawal

                                Saving Account                      Checking Account

                                                                         Check style
                                  Interest Rate                        Minimum Balance

                                Calculate interest

Management information system                     5_ 24                                  Huang Hong
                              The rocky mountain outfitters case class diagram
                                                                                              Inventory Item
          catalog                            Product Item
                                                                                               Inventory ID
          Season                              Product ID
                              1..* 0..*                                                            Size
           Year                                Vendor                                                                                    Shipper
        Description                            Gendor                 1         0..*                                                    Shipper ID
       EffectiveDate                         Description                                                                                  Name
         EndDate                                season                                                                                   Address
                                  1..*                                                         AverageCost
                                             NormalPrice                                                                               ContactNmae
            1..*                             SpecialPrice                                                                               Telephone
                                                                                                            1                                 1
            0..*         0..1                                      0..*
          Package                                                                                                                             0..*
                                             Return Item
        Package ID                                                                                 Order Item
                                              Quantity                                                                                   Shipment
        Description                                                                                 Quantity
                                                Price                                                                                  Tracking No.
         SalePrice                                                                                   Price
                                               Reason                                                                   1..*       1     DateSent
                                              Condition                                                                                 TimeSent
                                              Disposal                                                                                 ShippingCost
                                                            0..*                             1                                         TimeArrived
               Customer                                                                  Order
             Account No.                                                               Order ID
                 Name                                                                 Order Date
                                                                                                                                       Order Transaction
            Billing Address          1                               0..*            PriorityCode           1                   1..*
           ShippingAddress                                                        Shipping&Handling
                                                                                                                                       Transaction Type
              DayPhone                                                                    Tax
             NightPhone                                                               GrandTotal

                                           Web Order                          Telephone Order                      Mail Order
                                          EmailAddress                          PhoneClerk
                                          RepltMethod                          CallStartTime                      DateReceived
                                                                               LengthOfCall                       ProcessorClerk

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                          Where you are headed
        Requirements models for the traditional approach and the object-
         oriented approach are quite different.
        The traditional approach takes the event table and create a set of DFDs
         based on the information in the table, including the context diagram,
         DFD fragments and detailed DFDs, ERD, data flow definitions and
         process descriptions. These will be discussed in chapter 6
        The object-oriented approach takes the event table and create a set of
         use cases and use case diagrams, Class diagram,sequence diagrams,
         statechart diagrams. These will be discussed in chapter 7

Management information system         5_ 26                               Huang Hong
            Requirements models for the traditional approach
                   and the object-oriented approach
               object-oriented approach            Events and            traditional approach
                                                   Event table


             Use case                Class                   Entity-relationship          Context
             diagrams               Diagram                       diagram                 diagram


             Sequence               Statechart
                                                                 Detail DFDs             Diagram 0
             diagrams               diagrams

                        Other OO                                             Other
                         models                                            definitions

Management information system                    5_ 27                                          Huang Hong
        P161 review questions
        Draw an ERD and a class diagram to represent the readers and books
         and their relationship in a library.
        Case study: the real estate (房地产) multiple listing service system
               Real estate agent(房地产经纪人)
               Real estate office(房地产事务所)
               asking price n.索价, 要价
               Status code 状态码

Management information system       5_ 28                             Huang Hong

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