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Detail Design Subsystem Design Background and the Dynamic Part

Detail Design Subsystem Design Background and the Dynamic Part. Objectives: Subsystem Design. Understand the purpose of Subsystem Design and where in the lifecycle it is performed

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Detail Design Subsystem Design Background and the Dynamic Part

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  1. Detail Design Subsystem Design Background and the Dynamic Part

  2. Objectives: Subsystem Design • Understand the purpose of Subsystem Design and where in the lifecycle it is performed •  Define the behaviors specified in the subsystem's interfaces in terms of collaborations of contained classes (mentioned in Use Case Design) •  Document internal structure of the subsystem •  Determine the dependencies upon elements external to the subsystem that may be needed to support the responsibilities of the interface.

  3. Subsystem Design in Context in the UP At this time in ourDesign, we have defined classes, subsystems, their interfaces, and their dependencies. Have looked at components or sub-systems, i.e., ‘containers’ of complex behavior that we have treated as a black box. Now we need to flesh out the internal interactions, i.e., what classes exist in the subsystemand how do they collaborate to support responsibilities documented in the subsysteminterfaces. This is what subsystem design is all about. Architectural Analysis Review the Architecture Describe Architectural Describe Architecture Reviewer Architect Concurrency Design Distribution Subsystem Design Use-Case Analysis Review the Use-Case Design Design Design Designer Reviewer Class Design

  4. Subsystem Design in Context Here in subsystem design: We look at: 1) the detailed responsibilities of the subsystem and define and refine the classes needed to implement responsibilities, while 2) refining subsystem dependencies as needed. The internal interactions are expressed as collaborations of classes and possibly other components or subsystems. The focus is on the subsystem. The activity is iterative and recursive, but eventually feeds Class Design. Architectural Analysis Review the Architecture Describe Architectural Describe Architecture Reviewer Architect Concurrency Design Distribution Subsystem Design Use-Case Analysis Review the Use-Case Design Design Design Designer Reviewer Class Design

  5. Design Subsystems and Interfaces (updated) Design Subsystems and Interfaces DesignGuidelines Design Classes Use-Case Realization (updated) Subsystem Design Overview Subsystem Design is performed once per Design Subsystem. Purpose: to definethe behaviors specified in the interface via its contained classes: to document the internal structure of the subsystem, to define realizations between subsystem’s interface(s) and contained classes, & to determine the dependencies upon other subsystems. Subsystem Design Use-Case Realization

  6. <<subsystem>> Subsystem Name <<interface>> Interface Realization (Canonical form) Interface Subsystem <<subsystem>> Subsystem Name Interface Realization (Elided form) Review: Subsystems and Interfaces • Subsystem is a “cross between” a package and a class • Has semantics of a package • (i.e., can contain other model elements) • and a class (has behavior). • Subsystem realizes one or more interfaces which define its behaviors

  7. <<subsystem>> Subsystem Name <<interface>> Interface Realization (Canonical form) Interface Subsystem <<subsystem>> Subsystem Name Interface Realization (Elided form) Review: Subsystems and Interfaces • An interface is a model element which defines a set of behaviors (set of operations) offered by a classifier model element (e.g., class, subsystem or component). •  A classifier may realize one or more interfaces. •  An interface may be realized by one or more classifiers.

  8. <<subsystem>> Subsystem Name <<interface>> Interface Realization (Canonical form) Interface Subsystem <<subsystem>> Subsystem Name Interface Realization (Elided form) Review: Subsystems and Interfaces • Interfaces are not classes; provide no default behavior. • Realization is a semantic relationship between two classifiers – one serves as contract (the interface ‘class’) ; other, carries it out that is ‘realizes’ the contract. • via its subsystem contents and its dependencies

  9. <<subsystem>> A <<subsystem>> B <<subsystem>> C Key is abstraction and encapsulation Subsystem Guidelines • Goals • Loose coupling; as independent as possible • Insulation from change - minimized • Replaceable elements in the model. • Strong Suggestions for Subsystems: • Don’t expose details, only the interfaces • No element contained by a subsystem should have public visibility. • No elementoutside the subsystem should depend on a particular element inside the subsystem. • Only depend on interfaces of other model elements so that it is not directly dependent on any specific model element outside the subsystem.

  10. <<subsystem>> A <<subsystem>> B <<subsystem>> C Key is abstraction and encapsulation Subsystem Guidelines Exception: can share some class definitions done with packages in lower layers to ensure common definition of classes which must pass between subsystems All dependencies on a subsystem should be dependencies on the subsystem interfaces only!!  clients not dependent on inside!  subsystem can be replaced by different subsystem that realizes same interface.

  11. <<subsystem>> CourseCatalogSystem <<subsystem proxy>> CourseCatalogSystem ICourseCatalogSystem Modeling Convention for Subsystems and Interfaces Represent subsystems as three items in model: 1. <<subsystem>> package; 2. <<subsystem proxy>> class, 3. subsystem interface (class with stereotype <<interface>>). Subsystem package provides a container for the elements in the subsystem. The interaction diagrams describe how the subsystem elements collaborate to implement the operations of the interface the subsystem realizes, Note: <<subsystem proxy>> class actually realizes the interface and will orchestrate the implementation of the subsystem operations. Different (additional) interfaces would have their own proxy!

  12. Subsystem Design: Major Steps • Distribute Subsystem behaviors to Subsystem Elements • that is, the design components inside the subsystem. • Next, Document Subsystem Elements (e.g. classes…) • Document internal structural relationships among classes • Then document the interfaces upon which the subsystem itself is dependent. • Then, review the results of your subsystem design. • Now, let’s look at each of these

  13. <<subsystem>> CourseCatalogSystem <<interface>> ICourseCatalogSystem getCourseOfferings() Subsystem Responsibilities • Subsystem responsibilities defined by the interface it realizes •  When a subsystem realizes an interface, it makes a commitment to support every operation defined by the interface. •  Interface operations may be realized by • Internal class operations (which may require collaboration with other classes or subsystems) • An interface realized by a contained subsystem. subsystem responsibility

  14. Modeling Convention: Subsystem Interaction Diagrams - General Design Element 2 Subsystem Proxy Design Element 1 Subsystem Client performResponsibility( ) Op1() subsystem responsibility Internal subsystem interactions Op2() Op3() Op4() Subsystem interface not shown

  15. Modeling Convention: Subsystem Interaction Diagrams - General Design Element 2 Subsystem Proxy Design Element 1 Subsystem Client performResponsibility( ) Op1() subsystem responsibility Internal subsystem interactions Op2() Op3() Op4() • A message should be drawn from the <<subsystem>> client to the <<subsystem proxy>> • Note: interfacedoes not appear on internal subsystem interaction diagram. • Remainder of diagram should model howthe <<subsystem proxy>>classdelegates • responsibility for performing the invoked operation to the other subsystem elements. •  Recommend you name the interaction diagram <interface name>::<operation name>>. • This convention simplifies future tracing of interface behaviors to the classes implementing the • interface operations.

  16. Example: CourseCatalogSystem Subsystem In Context (1 of 2) subsystem interface : RegisterForCoursesForm : RegistrationController : ICourseCatalogSystem : Schedule : Student : Student 1: // create schedule( ) 2: // get course offerings( ) Student wishes to 3: getCourseOfferings(Semester) create a new schedule subsystem responsibility 4: // display course offerings( ) A list of the available • This sequence diagram sets the context of what will be performed in Subsystem Design. • Puts requirements on the subsystem, and • Is the primary input specification to the • task of creating local interactions • within the subsystem. course offerings for this semester are displayed Note: I have ‘cut’ a lot of detail out of this sequence diagram and the next one so that it is ‘easy’ to see the thrust of this slide…

  17. Example: CourseCatalogSystem Subsystem In Context (2 of 2) subsystem interface : RegisterForCoursesForm : RegistrationController : ICourseCatalogSystem : Schedule : Student : Student 1: // create schedule( ) 2: // get course offerings( ) 3: getCourseOfferings(Semester) subsystem responsibility Legacy RDBMS Database Access • The ICourseCatalogSystem::getCourseOfferings() • documentation specifies: “Retrieve the course • offerings available for the specified semester.” • So retrieval of the course offerings from legacy • database is responsibility of CourseCatalog system. • Now, must show exactly HOW this is done using the • RDBMS persistency mechanism. This will be shown • when we actually do the subsystem design (ahead)

  18. Review: Incorporating JDBC: Steps of Steps • (Done:) Provide access to the class libraries needed to implement JDBC; (i.e., Provide java.sql package) • (Done. Seen in Persistency:) Create the necessary DBClasses and their dependencies (for objects requiring persistency) • Remember, the proxy class is the class that manages the responsibilities of the subsystem as found in its interface. • You may think of it as a ‘control class’ for a particular interface. • Review slide 14 (and others) in lecture 29. DBClass and PersistentClassList and PersistentClass (and others) were stereotyped <<role>>, which implied their specific implementation is built by the designer when applying a mechanism such as persistency, legacy database access, etc. • Recall DBClass had methods like read(), update(), delete() create()… • In the next couple of slides, we are doing exactlythat with the DBCourseOffering class in attempting the access the legacy RDBMS to read data, execute a query, and more. • We have a DBCourseOffering along with CourseOfferingList and a CourseOffering to get results from executeQuery() (ahead) (continued)

  19. more • Note also that the Course Catalog System is clearly an Actor, which, of course, it should be, AND it is shown as such – in place – in the Sequence Diagram. • Note that the proxy class, DBCourseOffering, and the objects within java.sql are all involved in constituting the interface with the legacy RDBMS system. • So, we are seeing HOW the Course Catalog Subsystem via the proxy class and its dependencies are handling responsibilities. • Note that the next couple of slides do NOT have the caveat ‘Context.’ • They do not show the context for the subsystem or its interface; rather, this is the design implementation of the interface! • This is the subsystem design.

  20. CourseCatalog : : : Connection : Statement : : : ResultSet : Course Catalog System Client CourseCatalogSystem DBCourseOffering CourseOfferingList CourseOffering 1. getCourseOfferings(Semester) Retrieve all available course offerings for the current semester 1.1. read(string) 1.1.1. createStatement( ) sql statement is passed in 1.1.2. executeQuery(String) specifying the search criteria -- course offerings in the current 1.1.2.1. // executeQuery( ) semester Create a list to hold all retrieved course offerings 1.1.3. new( ) Repeat these operations for each element returned from the executeQuery() command. 1.1.4. new( ) The CourseOfferingList is loaded with the data retrieved from the 2. getString( ) database. 3. setData( ) The getData and setData operations are called for each attribute in the each retrieved 4. add(CourseOffering) class instance. Add the retrieved course offering to the list to be returned Ex: Local CourseCatalogSystem Subsystem Interaction • Internals of subsystems should yield interaction diagrams • that look like this. • We seecollaborations to implement the getCourseOfferings • operation of the ICourseCatalogSystem interface. • Recall: legacy system stores course offerings in an RDBMS. • Here we show how the RDBMS persistency mechanism • identified in Architectural Design is realized in the design. Subsystem Proxy (represents Subsystem) RDBMSRead CourseCatalogSystem (proxy) is in subsystem. DBCourseOffering object is created by designer (think DBClass in past lectures) as needed persistency and legacy interfacing. There is a dependency between the DBCourseOfferings and objects in java.sql starting with Connection and the actual access to the RDBMS via actor CourseCatalog. Note the design objects: CourseOfferingList and CourseOffering (no longer <<role>>

  21. CourseCatalog : : : Connection : Statement : : : ResultSet : Course Catalog System Client CourseCatalogSystem DBCourseOffering CourseOfferingList CourseOffering 1. getCourseOfferings(Semester) Retrieve all available course offerings for the current semester 1.1. read(string) 1.1.1. createStatement( ) sql statement is passed in 1.1.2. executeQuery(String) specifying the search criteria -- course offerings in the current 1.1.2.1. // executeQuery( ) semester Create a list to hold all retrieved course offerings 1.1.3. new( ) Repeat these operations for each element returned from the executeQuery() command. 1.1.4. new( ) The CourseOfferingList is loaded with the data retrieved from the 2. getString( ) database. 3. setData( ) The getData and setData operations are called for each attribute in the each retrieved 4. add(CourseOffering) class instance. Add the retrieved course offering to the list to be returned Ex: Local CourseCatalogSystem Subsystem Interaction • To read the course offerings, the persistency client requests • a service from the subsystem interface, represented by the • proxy class, who asks the DBCourseOffering class to retrieve a • course offerings for the specified semester. • DBCourseOffering creates a new statement using Connection • class’s createStatement() operation. • The statement is executed; data is returned to ResultSet object. • DBCourseOffering then creates a list of CourseOffering • instances, CourseOfferingList, populates it with retrieved • data, and returns it to the client. Subsystem Proxy RDBMSRead

  22. If we have time, we’ll go through the Billing System. But the ideas are the same… • Idea behind the Billing System is almost the same, but the Billing System does not require a persistency mechanism. • Start with the Billing subsystem interface object in the next slide at the end… • Really showing how the submitBill(Student, double) is implemented in the subsystem. But first: • Billing System in Context – then Local

  23. Example: Billing System Subsystem In Context subsystem interface : : : : : Schedule : Student. : : Registrar CloseRegistrationForm CloseRegistrationController ICourseCatalogSystem CourseOffering IBillingSystem • Here, will demonstrate design of a subsystem that does • not require a persistency mechanism. • This is at portion of the Close Registration use-case • realization sequence diagram. • The internals of the Billing System Subsystem • have not been designed yet. That is • the purpose of this activity, Subsystem Design 1. // close registration( ) 1.1. // is registration open?( ) Retrieve a list of course offerings for the current semester 2. // close registration( ) Close registration for 2.1. getCourseOfferings(Semester) each course Repeat twice this is If the maximum number of offering for simplicity; selected primary courses have 2.2. // close registration( ) realistically, an not been committed, select indefinite number of alternate course offerings). iterations could occur) 2.3. // level( ) Finally commit or 2.4. // close( ) Currently assuming tuition based on cancel the course number of offerings taken and certain offering once all attributes of students. If different offerings leveling has occurred get different prices this will change slightly. 2.5. getTuition( ) Send student and tuition to the Billing System, which will do the actual billing to the 2.6. submitBill(Student, double) student for the schedule. subsystem responsibility Now, we are really after the next slide…

  24. Example: Billing System Subsystem In Context subsystem interface : : : : : Schedule : Student. : : Registrar CloseRegistrationForm CloseRegistrationController ICourseCatalogSystem CourseOffering IBillingSystem • Here we put requirements on the subsystem, and • the sequence diagram is the primary input spec to • creating local interactions for the subsystem. • We see the operations subsystem must support. Shows • the simple way some client (CloseRegistrationController • here) deals with the task of submitting bill to • the legacy Billing System. 1. // close registration( ) 1.1. // is registration open?( ) Retrieve a list of course offerings for the current semester 2. // close registration( ) Close registration for 2.1. getCourseOfferings(Semester) each course Repeat twice this is If the maximum number of offering for simplicity; selected primary courses have 2.2. // close registration( ) realistically, an not been committed, select indefinite number of alternate course offerings). iterations could occur) 2.3. // level( ) Finally commit or 2.4. // close( ) Currently assuming tuition based on cancel the course number of offerings taken and certain offering once all attributes of students. If different offerings leveling has occurred get different prices this will change slightly. 2.5. getTuition( ) Send student and tuition to the Billing System, which will do the actual billing to the 2.6. submitBill(Student, double) student for the schedule. subsystem responsibility More coming…

  25. Explanation for next slides • The IBillingsystem::submitBill() documentation specifies • the following: “Billing information must be converted • into a format understood by the external Billing System • and then submitted to the external Billing System. • Thus the actual generation and submission of the bill is responsibility of the Billing System subsystem once the bill and proper parameters are passed to it. • But the billing information must be converted into a format that the Billing System can understand. • Let’s see how allthis is done…

  26. Example: Local BillingSystem Subsystem Interaction Subsystem Proxy Billing System : : : Student. : : Billing System Client BillingSystem StudentBillingTransaction BillingSystemInterface 1. submitBill(Student, double) Retrieve the information that must be included on the bill 1.1. create(Student, double) 1.1.1. // get contact info( ) 1.2. submit(StudentBillingTransaction) Logic here must convert the contract info into a format (StudentBillingTransaction) that the Billingsystem can understand. Given this, the proxy will orchestrate opening, processing, and closing the connection (and submitting the bill). No DBCourseOffering is needed here But StudentBillingTransaction is designed to convert data into a form the Billing System can understand from Student information and the ‘double.’ We simply see HOW the subsystem interface is realized. 1.2.1. // open connection( ) 1.2.2. // process transaction( ) 1.2.3. // close connection( )

  27. Example: Local BillingSystem Subsystem Interaction Subsystem Proxy Billing System : : : Student. : : Billing System Client BillingSystem StudentBillingTransaction BillingSystemInterface 1. submitBill(Student, double) Retrieve the information that must be included on the bill 1.1. create(Student, double) 1.1.1. // get contact info( ) 1.2. submit(StudentBillingTransaction) 1.2.1. // open connection( ) • The client object initiating the interaction • is abstracted. Again, we don’t care… • The BillingSystem subsystem proxy • class actually realizes the • IBillingSystem interface and drives this • realization by delegating the • implementation of the interface to the • subsystem elements. 1.2.2. // process transaction( ) 1.2.3. // close connection( )

  28. Example: Local BillingSystem Subsystem Interaction Subsystem Proxy Billing System : : : Student. : : Billing System Client BillingSystem StudentBillingTransaction BillingSystemInterface • The BillingSystem proxy class instance • creates a StudentBillingTransaction • specific to the external Billing System. • This transaction will be in a format that • the Billing System can process. • The StudentBillingTransaction knows • how to create itself using information • from the given Student. 1. submitBill(Student, double) Retrieve the information that must be included on the bill 1.1. create(Student, double) 1.1.1. // get contact info( ) 1.2. submit(StudentBillingTransaction) Note that only a single message is sent to the proxy: submitBill(…) The proxy, then, implements this responsibility by calling create(Student,double) and submit(StudentBillingTransaction). 1.2.1. // open connection( ) 1.2.2. // process transaction( ) 1.2.3. // close connection( ) After creating the StudentBillingTransaction, the BillingSystem proxy class instance submits the transaction to the class instance that actually communicates with the Billing System.

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