Detail Design
Subsystem Design
Background and the
Dynamic Part
1
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.
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
Describe
Distribution
Review the Architecture
Architecture Reviewer
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.
Subsystem Design
Use-Case
Analysis
This is what subsystem design is all about.
Review the
Design
Use-Case
Design
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
Architecture Reviewer
Subsystem Design
Use-Case
Analysis
Designer
Describe
Distribution
Review the
Design
Use-Case
Design
Design
Reviewer
The focus is on the subsystem.
The activity is iterative and
recursive, but eventually
feeds Class Design.
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


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
<<interface>>
Interface
Interface
<<subsystem>>
Subsystem Name
Realization (Canonical form)
Subsystem
<<subsystem>>
Subsystem Name
Interface
Realization (Elided form)
6
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.
<<interface>>
Interface
Interface
<<subsystem>>
Subsystem Name
Realization (Canonical form)
Subsystem
<<subsystem>>
Subsystem Name
Interface
Realization (Elided form)
7
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
<<interface>>
Interface
Interface
<<subsystem>>
Subsystem Name
Realization (Canonical form)
Subsystem
<<subsystem>>
Subsystem Name
Interface
Realization (Elided form)
8
Subsystem Guidelines


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

No element contained by a subsystem should
have public visibility.

No element outside 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.
<<subsystem>>
A
<<subsystem>>
B
<<subsystem>>
C
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!!
 clients not dependent on inside!
Key is abstraction
and encapsulation
<<subsystem>>
A
<<subsystem>>
B
<<subsystem>>
C
 subsystem can be replaced by different
subsystem that realizes same interface.
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. ICourseCatalogSystem
<<subsystem>>
CourseCatalogSystem
<<subsystem proxy>>
CourseCatalogSystem
Different (additional) interfaces would have their own proxy!
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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
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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.
<<interface>>
ICourseCatalogSystem
getCourseOfferings()
subsystem responsibility
<<subsystem>>
CourseCatalogSystem
13
Modeling Convention:
Subsystem Interaction Diagrams - General
Subsystem Client
Subsystem Proxy
Design Element 1
Design Element 2
performResponsibility( )
Op1()
subsystem
responsibility
Op2()
Internal subsystem
interactions
Op3()
Op4()
Subsystem interface not shown
16
Modeling Convention:
Subsystem Interaction Diagrams - General
Subsystem Client
Subsystem Proxy
Design Element 1
Design Element 2
performResponsibility( )
Op1()
subsystem responsibility
Op2()
Internal subsystem
interactions
Op3()
Op4()
• 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
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interface operations.
Example: CourseCatalogSystem Subsystem In Context
(1 of 2)
subsystem interface
: Student
: RegisterFor
CoursesForm
: Registration
Controller
: ICourseCatalog
System
: Schedule
: Student
1: // create schedule( )
2: // get course offerings( )
Student wishes to
create a new
schedule
3: getCourseOfferings(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
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…
• Is the primary input specification to the
task of creating local interactions
within the subsystem.
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Example: CourseCatalogSystem Subsystem In Context (2 of 2)
subsystem interface
: Student
: RegisterFor
CoursesForm
: Registration
Controller
: ICourseCatalog
System
: Schedule
: 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)
19
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)



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.



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.
Recall DBClass had methods like read(), update(), delete() create()…
In the next couple of slides, we are doing exactly that with the
(continued)
DBCourseOffering class in attempting the access
the legacy RDBMS
to read data, execute a query, and more.
We have a DBCourseOffering along with CourseOfferingList and20a
CourseOffering to get results from executeQuery() (ahead)
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.
21
Ex: Local CourseCatalogSystem Subsystem Interaction
CourseCatalog
System Client
:
:
CourseCatalogSystem DBCourseOffering
1. getCourseOfferings(Semester)
Subsystem Proxy
: Connection
: Statement
:
: Course Catalog CourseOfferingList
:
: ResultSet
CourseOffering
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 getCourseOfferings
operation of the ICourseCatalogSystem interface.
(represents Subsystem)
1.1. read(string)
• Recall: legacy system stores course offerings in an RDBMS.
1.1.1. createStatement( )
• Here we show how the RDBMS persistency mechanism
sql statement is passed in
identified in Architectural Design is realized in the design.
1.1.2. executeQuery(String)
specifying the search criteria -course offerings in the current
semester
Repeat these operations for each
element returned from the
executeQuery() command.
The CourseOfferingList is loaded
with the data retrieved from the
database.
The getData and setData
operations are called for each
attribute in the each retrieved
class instance.
1.1.2.1. // executeQuery( Create
)
a list to hold all
retrieved course offerings
1.1.3. new( )
1.1.4. new( )
RDBMS
Read
2. getString( )
3. setData( )
4. add(CourseOffering)
Add the retrieved course offering
to the list to be returned
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.
22
Note the design objects: CourseOfferingList and CourseOffering (no longer <<role>>
Ex: Local CourseCatalogSystem Subsystem Interaction
CourseCatalog
System Client
:
:
: Connection
CourseCatalogSystem DBCourseOffering
: Statement
:
: Course Catalog CourseOfferingList
:
: ResultSet
CourseOffering
• 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
Subsystem Proxy
class’s createStatement() operation.
1.1. read(string)
• The statement is executed; data is returned to ResultSet object.
1.1.1. createStatement( ) DBCourseOffering then creates a list of CourseOffering
instances, CourseOfferingList, populates it with retrieved
sql statement is passed in
1.1.2. executeQuery(String)
specifying the search criteria -data, and returns it to the client.
course offerings in the current
1.1.2.1. // executeQuery( Create
)
semester
a list to hold all
retrieved course offerings
1. getCourseOfferings(Semester)
Retrieve all available course
offerings for the current
semester
Repeat these operations for each
element returned from the
executeQuery() command.
The CourseOfferingList is loaded
with the data retrieved from the
database.
The getData and setData
operations are called for each
attribute in the each retrieved
class instance.
RDBMS
Read
1.1.3. new( )
1.1.4. new( )
2. getString( )
3. setData( )
4. add(CourseOffering)
Add the retrieved course offering
to the list to be returned
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
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


24
Example: Billing System Subsystem In Context
subsystem interface
:
:
:
:
: Registrar CloseRegistrationForm CloseRegistrationController ICourseCatalogSystem CourseOffering
1. // close registration( )
1.1. // is registration open?( )
: Schedule
: Student.
:
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
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. getCourseOfferings(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. getTuition( )
2.6. submitBill(Student, double)
subsystem responsibility
25
Now, we are really after the next slide…
Example: Billing System Subsystem In Context
subsystem interface
:
:
:
:
: Registrar CloseRegistrationForm CloseRegistrationController ICourseCatalogSystem CourseOffering
1. // close registration( )
1.1. // is registration open?( )
2. // close registration( )
Retrieve a list of course
offerings for the current
semester
2.1. getCourseOfferings(Semester)
Repeat twice this is
for simplicity;
realistically, an
indefinite number of
iterations could
occur)
: Schedule
: Student.
:
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. Show
the simple way some client (CloseRegistrationControlle
here) deals with the task of submitting bill to
Close
registration for the legacy Billing System.
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. getTuition( )
2.6. submitBill(Student, double)
subsystem responsibility
26
More coming…
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 all this is done…
27
Example: Local BillingSystem Subsystem Interaction
Subsystem Proxy
Billing System
Client
:
BillingSystem
:
StudentBillingTransaction
1. submitBill(Student, double)
1.1. create(Student, double)
: Student.
:
BillingSystemInterface
: Billing System
Retrieve the
information that must
be included on the bill
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).
1.2.1. // open connection( )
1.2.2. // process transaction( )
1.2.3. // close connection( )
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.
28
Example: Local BillingSystem Subsystem Interaction
Subsystem Proxy
Billing System
Client
:
BillingSystem
:
StudentBillingTransaction
1. submitBill(Student, double)
1.1. create(Student, double)
: Student.
:
BillingSystemInterface
: Billing System
Retrieve the
information that must
be included on the bill
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( )
29
Example: Local BillingSystem Subsystem Interaction
Subsystem Proxy
Billing System
Client
:
BillingSystem
:
StudentBillingTransaction
1. submitBill(Student, double)
1.1. create(Student, double)
: Student.
:
BillingSystemInterface
: Billing System
• The BillingSystem proxy class instance
Retrieve the
information that must creates a StudentBillingTransaction
be included on the bill specific to the external Billing System.
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).
• 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.
1.2.1. // 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.
30