Detail Design Subsystem Design Background and the Dynamic

Detail Design Subsystem Design Background and the Dynamic Part 1

Objectives: Subsystem Design n n 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. 2

Subsystem Design in Context in the UP At this time in our Design, 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. Architectural Analysis Describe Architectural Concurrency Design Architect Now we need to flesh out the internal interactions, i. e. , what classes exist in the subsystem and how do they Designer collaborate to support responsibilities documented in the subsystem interfaces. Review the Architecture Reviewer Subsystem Design Use-Case Analysis This is what subsystem design is all about. Describe Distribution Review the Design Use-Case Design Reviewer Class Design 3

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. Architectural Analysis Describe Architectural Concurrency Design Architect The internal interactions are expressed as collaborations of classes and possibly other components or subsystems. Review the Architecture Reviewer Subsystem Design Use-Case Analysis Designer Describe Distribution Review the Design Use-Case Design Reviewer The focus is on the subsystem. The activity is iterative and recursive, but eventually feeds Class Design 4

Subsystem Design Overview Subsystem Design is performed once per Design Subsystem. Purpose: to define the 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. Design Subsystems and Interfaces Use-Case Realization Design Guidelines Design Subsystems and Interfaces (updated) Subsystem Design Use-Case Realization (updated) Design Classes 5

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

Review: Subsystems and Interfaces n n n 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. <<interface>> Interface <<subsystem>> Subsystem Name Realization (Canonical form) Subsystem <<subsystem>> Subsystem Name Interface Realization (Elided form) 7

Review: Subsystems and Interfaces n n 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 <<interface>> Interface <<subsystem>> Subsystem Name Realization (Canonical form) Subsystem <<subsystem>> Subsystem Name Interface Realization (Elided form) 8

Subsystem Guidelines n n Key is abstraction and encapsulation 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 <<subsystem>> A <<subsystem>> B ¨ No element contained by a subsystem should have public visibility. ¨ No element outside the subsystem should depend on a particular element inside the subsystem. depend on interfaces of other model elements so that it is not directly dependent on any specific model element outside the subsystem. <<subsystem>> C ¨ Only 9

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!! Key is abstraction and encapsulation <<subsystem>> A <<subsystem>> B <<subsystem>> C clients not dependent on inside! subsystem can be replaced by 10

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. ICourse. Catalog. System <<subsystem>> Course. Catalog. System <<subsystem proxy>> Course. Catalog. System Different (additional) interfaces would have their own proxy! 11

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

Subsystem Responsibilities n n n 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. <<interface>> ICourse. Catalog. System get. Course. Offerings() subsystem responsibility <<subsystem>> Course. Catalog. System 13

Modeling Convention: Subsystem Interaction Diagrams - General Subsystem Client Subsystem Proxy Design Element 1 Design Element 2 perform. Responsibility( ) Op 1() subsystem responsibility Op 2() Internal subsystem interactions Op 3() Op 4() Subsystem interface not shown 16

Modeling Convention: Subsystem Interaction Diagrams - General Subsystem Client Subsystem Proxy Design Element 1 Design Element 2 perform. Responsibility( ) Op 1() subsystem responsibility Op 2() Internal subsystem interactions Op 3() Op 4() • A message should be drawn from the <<subsystem>> client to the <<subsystem proxy>> • Note: interface does not appear on internal subsystem interaction diagram. • Remainder of diagram should model how the <<subsystem proxy>> class delegates 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 17 interface operations.

Example: Course. Catalog. System Subsystem In Context (1 of 2) subsystem interface : Student : Register. For Courses. Form : Registration Controller : ICourse. Catalog System : Schedule : Student 1: // create schedule( ) Student wishes to create a new schedule 2: // get course offerings( ) 3: get. Course. Offerings(Semester) 4: // display course offerings( ) A list of the available course offerings for this semester are displayed subsystem responsibility • 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 Note: I have ‘cut’ a lot of detail task of creating local interactions out of this sequence diagram and within the subsystem. the next one so that it is ‘easy’ to see thrust of this slide… 18

Example: Course. Catalog. System Subsystem In Context (2 of 2) subsystem interface : Student : Register. For Courses. Form : Registration Controller : ICourse. Catalog System : Schedule : Student 1: // create schedule( ) 2: // get course offerings( ) 3: get. Course. Offerings(Semester) subsystem responsibility Legacy RDBMS Database Access • The ICourse. Catalog. System: : get. Course. Offerings() documentation specifies: “Retrieve the course offerings available for the specified semester. ” • So retrieval of the course offerings from legacy database is responsibility of Course. Catalog 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) 19

Review: Incorporating JDBC: Steps of Steps n n (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. ¨ n Review slide 14 (and others) in lecture 29. DBClass and Persistent. Class. List and Persistent. Class (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. ¨ n n Recall DBClass had methods like read(), update(), delete() create()… In the next couple of slides, we are doing exactly that with the (continued) DBCourse. Offering class in attempting the access the legacy RDBMS to read data, execute a query, and more. We have a DBCourse. Offering along with Course. Offering. List and 20 a Course. Offering to get results from execute. Query() (ahead)

more n 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. n Note that the proxy class, DBCourse. Offering, and the objects within java. sql are all involved in constituting the interface with the legacy RDBMS system. n So, we are seeing HOW the Course Catalog Subsystem via the proxy class and its dependencies are handling responsibilities. n 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! 21 ¨ This is the subsystem design.

Ex: Local Course. Catalog. System Subsystem Interaction Course. Catalog : : System Client Course. Catalog. System DBCourse. Offering 1. get. Course. Offerings(Semester) Subsystem Proxy : Connection : Statement : : Course Catalog Course. Offering. List : Course. Offering : Result. Set Retrieve all available course • Internals of subsystems should yield interaction diagrams offerings for the current that look like this. semester • We see collaborations to implement the get. Course. Offerings operation of the ICourse. Catalog. System interface. (represents Subsystem) 1. 1. read(string) • Recall: legacy system stores course offerings in an RDBMS 1. 1. 1. create. Statement( ) • Here we show the RDBMS persistency mechanism sql statement is passed in identified in Architectural Design is realized in the design. 1. 1. 2. execute. Query(String) specifying the search criteria -course offerings in the current semester Repeat these operations for each element returned from the execute. Query() command. The Course. Offering. List is loaded with the data retrieved from the database. The get. Data and set. Data operations are called for each attribute in the each retrieved class instance. 1. 1. 2. 1. // execute. Query( Create ) a list to hold all retrieved course offerings 1. 1. 3. new( ) 1. 1. 4. new( ) RDBMS Read 2. get. String( ) 3. set. Data( ) 4. add(Course. Offering) Add the retrieved course offering to the list to be returned Course. Catalog. System (proxy) is in subsystem. DBCourse. Offering object is created by designer (think DBClass in past lectures) as needed persistency and legacy interfacing. There is a dependency between the DBCourse. Offerings and objects in java. sql starting with Connection and the actual access to the RDBMS via actor Course. Catalog. 22 Note the design objects: Course. Offering. List and Course. Offering (no longer <<role>>

Ex: Local Course. Catalog. System Subsystem Interaction Course. Catalog : : System Client Course. Catalog. System DBCourse. Offering : Connection : Statement : : Course Catalog Course. Offering. List : : Result. Set Course. Offering • To read the course offerings, the persistency client requests a service from the subsystem interface, represented by the proxy class, who asks the DBCourse. Offering class to retrieve a course offerings for the specified semester. • DBCourse. Offering creates a new statement using Connection Subsystem Proxy class’s create. Statement() operation. 1. 1. read(string) • The statement is executed; data is returned to Result. Set object. 1. 1. 1. create. Statement( ) DBCourse. Offering then creates a list of Course. Offering instances, Course. Offering. List, populates it with retrieved sql statement is passed in 1. 1. 2. execute. Query(String) specifying the search criteria -data, and returns it to the client. course offerings in the current 1. 1. 2. 1. // execute. Query( Create ) semester a list to hold all retrieved course offerings 1. get. Course. Offerings(Semester) Retrieve all available course offerings for the current semester Repeat these operations for each element returned from the execute. Query() command. The Course. Offering. List is loaded with the data retrieved from the database. The get. Data and set. Data operations are called for each attribute in the each retrieved class instance. RDBMS Read 1. 1. 3. new( ) 1. 1. 4. new( ) 2. get. String( ) 3. set. Data( ) 4. add(Course. Offering) Add the retrieved course offering to the list to be returned 23

n If we have time, we’ll go through the Billing System. But the ideas are the same… n Idea behind the Billing System is almost the same, but the Billing System does not require a persistency mechanism. n Start with the Billing subsystem interface object in the next slide at the end… Really showing how the submit. Bill(Student, double) is implemented in the subsystem. But first: Billing System in Context – then Local n n 24

Example: Billing System Subsystem In Context subsystem interface : : : Registrar Close. Registration. Form Close. Registration. Controller ICourse. Catalog. System Course. Offering 1. // close registration( ) 1. 1. // is registration open? ( ) : Schedule : Student. : IBilling. System • Here, will demonstrate design of a subsystem that does not require a persistency mechanism. • This is at portion of the Close Registration use-case Retrieve a list of course offerings for the current realization sequence diagram. semester The internals of the Billing System Subsystem Close have not been designed yet. That is 2. 1. get. Course. Offerings(Semester) registration for the purpose of this activity, Subsystem Design 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( ) 2. // close registration( ) Finally commit or cancel the course offering once all leveling has occurred Send student and tuition to the Billing System, which will do the actual billing to the student for the schedule. 2. 4. // close( ) Currently assuming tuition based on number of offerings taken and certain attributes of students. If different offerings get different prices this will change slightly. 2. 5. get. Tuition( ) 2. 6. submit. Bill(Student, double) subsystem responsibility 25 Now, we are really after the next slide…

Example: Billing System Subsystem In Context subsystem interface : : : Registrar Close. Registration. Form Close. Registration. Controller ICourse. Catalog. System Course. Offering : Schedule : Student. : IBilling. System • Here we put requirements on the subsystem, and the sequence diagram is the primary input spec to 1. // close registration( ) creating local interactions for the subsystem. 1. 1. // is registration open? ( ) Retrieve a list of course • We see the operations subsystem must support. Show offerings for the current the simple way some client (Close. Registration. Controlle semester 2. // close registration( ) here) deals with the task of submitting bill to Close 2. 1. get. Course. Offerings(Semester) registration for the legacy Billing System. Repeat twice this is for simplicity; realistically, an indefinite number of iterations could occur) each course offering 2. 2. // close registration( ) If the maximum number of selected primary courses have not been committed, select alternate course offerings). 2. 3. // level( ) Finally commit or cancel the course offering once all leveling has occurred Send student and tuition to the Billing System, which will do the actual billing to the student for the schedule. 2. 4. // close( ) Currently assuming tuition based on number of offerings taken and certain attributes of students. If different offerings get different prices this will change slightly. 2. 5. get. Tuition( ) 2. 6. submit. Bill(Student, double) subsystem responsibility 26 More coming…

Explanation for next slides • The IBillingsystem: : submit. Bill() 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 the Billing System can understand. Let’s see how all this is done… 27

Example: Local Billing. System Subsystem Interaction Subsystem Proxy Billing System Client : Billing. System : Student. Billing. Transaction 1. submit. Bill(Student, double) 1. 1. create(Student, double) : Student. : Billing. System. Interface : Billing System Retrieve the information that must be included on the bill 1. 1. 1. // get contact info( ) 1. 2. submit(Student. Billing. Transaction) Logic here must convert the contract info into a format (Student. Billing. Transaction) that the Billingsystem can understand. Given this, the proxy will orchestrate opening, processing, and closing the connection (and submitting the bill). 1. 2. 1. // open connection( ) 1. 2. 2. // process transaction( ) 1. 2. 3. // close connection( ) No DBCourse. Offering is needed here But Student. Billing. Transaction 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. 28

Example: Local Billing. System Subsystem Interaction Subsystem Proxy Billing System Client : Billing. System : Student. Billing. Transaction 1. submit. Bill(Student, double) 1. 1. create(Student, double) : Student. : Billing. System. Interface : Billing System Retrieve the information that must be included on the bill 1. 1. 1. // get contact info( ) 1. 2. submit(Student. Billing. Transaction) 1. 2. 1. // open connection( ) • The client object initiating the interaction is abstracted. Again, we don’t care… • The Billing. System subsystem proxy class actually realizes the IBilling. System 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( ) 29

Example: Local Billing. System Subsystem Interaction Subsystem Proxy Billing System Client : Billing. System : Student. Billing. Transaction 1. submit. Bill(Student, double) 1. 1. create(Student, double) : Student. : Billing. System. Interface : Billing System • The Billing. System proxy class instance Retrieve the information that must creates a Student. Billing. Transaction be included on the bill specific to the external Billing System. 1. 1. 1. // get contact info( ) 1. 2. submit(Student. Billing. Transaction) Note that only a single message is sent to the proxy: submit. Bill(…) The proxy, then, implements this responsibility by calling create(Student, double) and submit(Student. Billing. Transaction). • This transaction will be in a format the Billing System can process. • The Student. Billing. Transaction knows how to create itself using information from the given Student. 1. 2. 1. // open connection( ) 1. 2. 2. // process transaction( ) 1. 2. 3. // close connection( ) After creating the Student. Billing. Transaction, the Billing. System proxy class instance submits the transaction to the class instance that actually communicates with the Billing System. 30