CISC 323 Intro to Software Engineering Week 8: Software - - PowerPoint PPT Presentation

CISC 323 Intro to Software Engineering

Week 8: Software Architecture (Continued)

CISC 323 Intro to Software Engineering

Lecture 8-1 Data-Centered and Interpreter Architectural Styles

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Architectural Style Examples

[Shaw&Garlan]

• Pipes and Filters
• Layers
• Event-Based
• Data-Centered
• Interpreter
• PAC

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Data-Centered Architecture Style

• Repository

– Allows data to be allowing shared amongst a set

• f components
• Blackboard

– Active repository cooperative, distributed decision making

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Repository

• Set of components

share data

• E.g., database or data

structure shared by multiple components

• Connectors permit

components to read/write to repository

Repository

Example

• Compiler based on pipes and filter

architecture style

• Parse tree is complex data structure

passed between phases

• Needs to be converted into a stream

that can be passed over a pipe --

• verhead
• Use repository to represent abstract

syntax tree

Scanner Parser Semantic Analyzer Code Generator

program text executable code tokens parse tree parse tree

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Compiling as Pipe and Filter Architecture Augmented with Repository

Scanner Parser Semantic Analyzer Code Generator

program text executable code tokens control control

Repository: Parse Tree

Control information passed between phases rather than parse tree

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Properties of Repository Architecture Style

• Performance

– For complex data structures, saves overhead

• f passing data structure

from one component to another – If components on different machines, this overhead might be considerable – If components on different machines, cost of accessing repository might be high

Repository c1 c2 c3

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Properties of Repository Architecture Style

• Performance

– E.g., if components and repositories on different machines, each call to repository goes over network – Need to balance this cost vs cost of moving data between phases using pipes and filters – E.g., if c2 makes 1000 calls for information to repository, each call takes 1 ms, total time = 1 s. Compare to time to pass repository from c1 to c2

Repository c1 c2 c3

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Properties of Repository Architecture Style

• Performance

– Need to ensure repository can scale to load of components making requests of it – Ideally, do not want components waiting while repository operates on long queue of requests – This analysis is complex, out

• f scope of this course

Repository c1 c2 c3

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Properties of Repository Architecture Style

• Development Time

– Numerous infrastructures for repositories already exist -- e.g.

• Commercial databases
• Java Remote Method

Invocation (RMI)

– Need to balance savings in development time vs need to learn infrastructures

Repository c1 c2 c3

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Properties of Repository Architecture Style

• Security

– Repository potentially available to anyone who can connect to it – Particularly dangerous in distributed setting where repository available via Internet protocol – E.g., don’t want medical patient information available to anyone who knows IP address of medical database

Repository c1 c2 c3

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Properties of Repository Architecture Style

• Availability

– Repository becomes critical component in system – Failure in repository causes entire system to fail

Repository c1 c2 c3

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Blackboard Architecture Style

• Variant of repository
• Repository is active

– Can activate components in response to changes in blackboard contents

• Typical application

– Use blackboard to mediate cooperative activity amongst components – Tasks where desired

• utcome is imprecisely

defined or error prone

Blackboard c1 c2 c3 Update/request information from repository Activate components as new information becomes available

HTTP Server

(e.g. Apache)

HTTP Client

(e.g., Netscape, Internet Explorer)

Order System Inventory Catalogue

Requests for book info, delivery times, orders, etc. HTML document Requests for book info Requests for delivery time Order placement Request availability

Recall example of

• nline book ordering

system...

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Example: Inventory System using the Blackboard Architecture

• Inventory blackboard used to

coordinate filling orders

• Order system initiates orders
• Receiver records new stock as it

arrives

• Shipper sends order to be

packaged

• All communication via inventory

Order System Inventory

Request availability

Receiver Shipper

Record new stock Record stock shipped Inform

• rder filled

Initiate shipping Order stock

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Example: Smart office

• Tracking who is in the office

– Using: Active badges, voice recognition, cameras – Allows

• Ease of finding colleagues
• User authentication (no need to have door keys, logins at

machines)

• People’s environments to follow them

– Sitting down at someone else’s PC is just like sitting down at your own

• Smart commands

– Use gestures/voice to

• Turn on projector, connect to PC
• Record contents of whiteboard save them under my username

– Combine modalities

• Say “Save *this* on my laptop”, while pointing at whiteboard

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Example: Smart office

• Application depends on combining a set of

physical devices

– Cameras, microphones, door switches

• and a set of services

– Voice recognition speech recognition, gesture recognition

• and a set of models

– Who is in room, what command are they executing

Microphone Camera1 Cameran

• Active Badge

Reader Voice samples Badge data Camera inputs People detector Model: people in room Command detector Model: command

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Interesting scenarios

• Person enters room, but their active badge is malfunctioning
• When they first speak, voice recognition detects their presence

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Architectural Style Examples

[Shaw&Garlan]

• Pipes and Filters
• Layers
• Event-Based
• Data-Centered
• Interpreter
• PAC

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Interpreter Architecture Style

• Develop domain-specific language for problem area
• Express solution in terms of this language
• Include interpreter in system to evaluate the solution
• Motivation

– Providing higher level language for problem domain simplifies programming problem – Examples

• XML parsers
• Extensible interpreters such as JVM, tcl
• Rule-based/expert systems

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Interpreter Architecture [Shaw&Garlan p. 27]

Program state Program being interpreted Simulated Interpretation Engine Internal Interpreter State inputs

• utputs

selected instruction selected data program code

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E.g., Interpreting Java Programs

Program state Java class files Java Virtual Machine (JVM) JVM State inputs

• utputs

selected instruction selected data program code

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Interpreting Java Programs

• Java programs are

represented as a set of class files

– Contain byte code describing operations on the Java Virtual Machine

• These programs are

executed as if they were being run on a native machine

• Program state is actually

represented in JVM Program state Java class files Java Virtual Machine (JVM) JVM State inputs

• utputs

selected instruction selected data program code

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Example: Processing XML

• XML (eXtensible Markup Language) is a way of encoding

structured data for

– Archiving – Interchanging between applications – Sending over the Internet

• (e.g. e-commerce business-to-business applications)
• XML processing is implemented via the interpreter architecture

style

See e.g. http://www.xml101.com:8081/xml/

XML

• XML documents consist of tagged text
• Tags indicate semantics of data
• Tags may be arbitrary

– Follow format of

<tagname attr1=value1,…,attrn=valuen>

contents

</tagname>

<books> <book isbn=”0201199300"> <title>Software Architecture in Practice</title> <author>Len Bass</author> <author>Paul Clements</author> <author>Rick Kazman</author> </book> </books>

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XML DTD’s

• A DTD (Document Type Definition) describes legal use of tags in a

particular kind of XML document

<!DOCTYPE listOfBooks [

<!ELEMENT books (book*)> <!ELEMENT book (title,author+)> <!ATTLIST book isbn CDATA “0”> <!ELEMENT title (#CDATA)> <!ELEMENT author (#CDATA)>

]> <listOfBooks>

<books> <book isbn=”0201199300"> <title>Software Architecture in Practice</title> <author>Len Bass</author> <author>Paul Clements</author> <author>Rick Kazman</author> </book> </books> Example document following this DTD

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DTD’s specify

• What tags are legal
• How tags are combined

– A book must have a title and 1 or more authors – A set of books consists of 0 or more books – A book has an ISBN attribute (unique number for books), which is character text (CDATA), with a default value of “0”

<books> <book isbn=”0201199300"> <title>Software Architecture in Practice</title> <author>Len Bass</author> <author>Paul Clements</author> <author>Rick Kazman</author> </book> </books>

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Using XML in a System for Ordering Books

Component for converting book

• rders from XML to

Java classes Book order as Java class Book order as XML document

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Using XML in a System for Ordering Books

Books DTD XML Processor DTD Book order as Java class Book order as XML document Component for converting book

• rders from XML

to Java classes

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Using XML in a System for Ordering Books

Books DTD XML Processor Book order Web Browser (XML document) Order Processor DTD Books data structure XML Order Other components…

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XML Processor for Ordering Books

• XML Processor is an interpreter for DTD’s
• When given the Books DTD, becomes a component

capable of processing book orders

• Advantages

– Can reuse XML processor in many contexts – If format of book orders change, just need to change DTD, not code

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Attributes of Interpreter Style

• Development Time

– Tremendous potential for reuse

• Performance

– Interpretation may be slower than hand-coded solutions

• Modifiability

– Can be improved by restricting modification to data being interpreted

CISC 323 Intro to Software Engineering

Lecture 8-2 PAC Architectural Style

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Architectural Style Examples

[Shaw&Garlan]

• Pipes and Filters
• Layers
• Event-Based
• Data-Centered
• Interpreter
• PAC

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The PAC Architecture Style

• Supporting development of user interfaces
• Conceptual architecture that can be mapped to

multiple concrete architectures

• Agent-based

– Program decomposed into a set of agents, each responsible for some part of the task of interacting with the user

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Example: PAC Architecture for a Set of Buttons

• Assume an interface has a set of buttons

controlling navigation

– “Back” means return to previous page in history, “Forward” means go forward to last page we moved back from (if there is

• ne)

Button

List of pages visited Current page

• “Back” decrements current page counter
• “Forward” increments current page counter
• If current page is front of list, “Back” button is disabled
• If current page is end of list, “Forward button is disabled
• Going to a new page enqueues that page after the current

page, sets current page to that page

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Starting with Just a Button...

• Buttons have

– A label (e.g. “Back”, “Forward”) – A state (disabled, enabled)

• Buttons have local behaviour

– “Rollover” - become highlighted when mouse moves over them – Become depressed following mouse down – Become released following mouse up

Enabled button Disabled button “Rolled over” button Depressed button

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Button Abstraction

• A button’s state is therefore

– Label (String value) – Is Enabled? (Boolean value) – Is “rolled over”? (Boolean value) – Is depressed? (Boolean value)

• Therefore, the state of a button is captured in three Boolean

values and a string value

• In PAC, this state is called the button’s Abstraction

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PAC Components

• PAC architectures

constructed from a set of components

• Each component

composed of three facets

– Presentation: handles user input and redraws the display – Abstraction: underlying state of interactive entity – Control: mediates communication between Presentation, Abstraction and other PAC components

Presentation Abstraction

Control

• ther PAC components
• ther PAC components

Inter-facet communication, typically event or method call

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PAC Button

• Abstraction

– Java object containing methods to set/get

• Button label
• Enabled/disabled state
• Rolled-over state
• Depressed/released state

Presentation Abstraction

Control

• ther PAC components
• ther PAC components

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PAC Button

• Presentation

– Accepts mouse input

• mouse down

– If button enabled, depresses button

• mouse up

– If button depressed, releases button

• mouse enter

– If active, puts button in rollover state

• mouse leave

– If rolled over, removes rollover state

Presentation Abstraction

Control

• ther PAC components
• ther PAC components

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PAC Button

• Presentation

– Responsible for redrawing button

• When changes in enabling,

depressed/released, rolled over, redraws with appropriate animation, GIF image

Presentation Abstraction

Control

• ther PAC components
• ther PAC components

Question: Why doesn’t input part of Presentation simply handle redrawing?

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Building an Architecture with PAC Components

• Require a PAC component for each button
• Require a component for navigation
• Require components for the rest of the

browser, such as the display of the web page

Button

List of pages visited Current page

• “Back” decrements current page counter
• “Forward” increments current page counter
• If current page is front of list, “Back” button is disabled
• If current page is end of list, “Forward button is disabled
• Going to a new page enqueues that page after the current

page, sets current page to that page

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PAC Architecture

P A

C

P A

C

P A

C

P A

C

Back Button Forward Button Web Page Navigation

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Navigation Component

• Abstraction contains queue of

pages, current page pointer

• If there are pages before

current page, enables back button

• If there are pages after

current page, enables forward button

• Actions from buttons

manipulate current page

• No Presentation facet

required

Presentation Abstraction

Control

• ther PAC components

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Scenario: Go Back One Page

P A

C

P A

C

P A

C

P A

C

Back Button Forward Button Web Page Navigation Current page Initial state: current page is end of queue, therefore “Forward” button is inactive. I.e., we have never clicked the back button

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Scenario: Go Back One Page

P A

C

P A

C

P A

C

P A

C

Back Button Forward Button Web Page Navigation Current page Final state: current page is moved back

• ne position in the queue; the new web

page is displayed, and the forward button becomes enabled

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Scenario: Go Back One Page

P A

C

P A

C

P A

C

P A

C

Back Button Forward Button Web Page Navigation

• 1. User clicks mouse down; P informs C that

mouse clicked down; C informs A that button depressed; C informs P that button should be redrawn; P redraws button

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Scenario: Go Back One Page

P A

C

P A

C

P A

C

P A

C

Back Button Forward Button Web Page Navigation

• 2. User releases mouse; P informs C that

mouse released; C informs A that button released; C informs P that button should be redrawn; P redraws button; C informs Navigation that Back button has been clicked

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Scenario: Go Back One Page

P A

C

P A

C

P A

C

P A

C

Back Button Forward Button Web Page Navigation

• 3. C informs A that current page moved back
• ne. C informs forward button that it is enabled.

C informs web page that new page needs to be drawn.

CISC 323 Intro to Software Engineering

Lecture 8-3 Example: COM and the Object-oriented Architectural Style

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Case Study

• Microsoft’s COM architecture

– Component Object Model – Used for building Microsoft’s large applications

• Word, Excel, PowerPoint, …

– Variants

• DCOM (distributed version)
• OLE (Object Linking and Embedding)

– Built on top of COM to allow document types to be combined

• ActiveX (Web version)
• .NET – replaces DCOM and some of the higher-level

infrastructure

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Microsoft OLE

• Combines

– Object-Oriented Architecture Style – Interpreter Architecture Style – Layer Architecture Style – Event-Driven Architecture Style

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Motivation: Object Embedding

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Motivation: Object Embedding

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Motivation: Object Embedding

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Motivation: Object Embedding

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What’s Actually Going On...

• Microsoft applications are made up of a set of

components

• E.g., in Word

– Document component holds the value of one document – Window component implements UI functionality of

• ne window

– List component holds formatting information for a list in a document – Etc…

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What’s Really Going On...

• Similarly, Excel spreadsheet documents are made up
• f a number of components
• COM (Component Object Model) allows our Word

document to embed elements of spreadsheet documents

• Therefore create a compound document involving

both Word and Excel components

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COM as a Layered System

(Idealized View)

COM DCOM OLE ActiveX

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COM as a Layered System

(Idealized View)

COM DCOM OLE ActiveX Mechanism for connecting together software components. Components have an interface (similar to methods). Applications are made up of a set of components, but components may be shared amongst more than one application. Components can be in different languages.

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COM as a Layered System

(Idealized View)

COM DCOM OLE ActiveX Like COM, but components don’t all have to be on the same machine.

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COM as a Layered System

(Idealized View)

COM DCOM OLE ActiveX Object Linking and Embedding: Simple mechanism for embedding documents of one type within

• another. E.g., if you want a

spreadsheet within a Word document, embed a spreadsheet managed by Excel.

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COM as a Layered System

(Idealized View)

COM DCOM OLE ActiveX Allows delivery of components

• ver the web. In web browser,

special tag indicates that the URL content is not an HTML page, but a COM component that is to be downloaded and

• executed. Simplifies delivery
• f programs, since no

installation CD required.

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COM as a Layered System

(Slightly more accurate view)

COM DCOM OLE ActiveX

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COM as an OO System

• Applications are built as a set of COM components
• These components are constructed using standard

OO techniques

– Inheritance – Aggregation – Polymorphism

References:

• D. Mackenzie, Word 2000 VBA, WROX Press, 1999
• D. Chappell, Understanding ActiveX and OLE, Microsoft Press, 1996

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A Visual Basic COM (OLE) Program

For fun, try running this in MS Word - select Tools|Macro|Visual Basic Editor

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Result of Running the Program within MS Word

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A Visual Basic COM (OLE) Program

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Result of Running the Program within MS Word

An application contains a set of documents, which in turn contain many

• ther objects. Examples include the set of

characters (sentences, words) in the document, the currently selected range, the document’s styles, and many, many

• thers.

OO Design of MS Word

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OO Design

• f MS Word

A range represents a section of text over which editing operations can be performed. A range contains many properties, such as the set of characters/sentences/words in the range, the set of fonts used, the paragraph format, the set of errors returned by checking tools, and many more.

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Example Operations

• Range

– void insertBefore (String) -- inserts given string before the range – void cut ()-- copies the range to the clipboard, deletes the range – void sort (…) -- sorts the range according to given parameters – SpellingSuggestions getSpellingSuggestions (…) -- returns spelling suggestions for any misspelled words in the range – long delete (Unit, Count) -- deletes count number of unit items – …and dozens more…

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Connectors in COM

• COM components can be created in many different

languages

– E.g., C++, Java, C#, Visual Basic, …

• Components can reside in different applications, in

the operating system and (with DCOM) on different machines

• Connectors therefore are not simple method call

connectors

– What object do you call? – What format are parameters in? E.g., when passing a Visual Basic object as a parameter to a C++ COM object?

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Connecting COM Components

• Components provide interfaces

– Language-independent points of service – Interfaces described in Interface Definition Language (IDL) – Language-dependent IDL translators transform method calls from native language to IDL format – IDL is very close to C++, so C++ translation is trivial

COM Component Interface

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Example IDL Specification

[object, uuid(E7CD0D00-1827-11CF-9946-444553540000) ] interface ISpellChecker : IUnknown { import “unknwn.idl”; HRESULT LookupWord([in] OLECHAR word[31], [out] boolean *found); HRESULT AddToDictionary([in] OLECHAR word[31]); HRESULT RemoveFromDictionary([in] OLECHAR word[31]); }

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Connecting COM Components

Calling Component Called Component IDL Specification IDL Translator

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The Object-Oriented Architectural Style

• Object-orientation can be seen as an

architectural style

– Components = objects – Connectors = call

• We have already seen the fundamental

elements of object-orientation

– Encapsulation – Inheritance – Polymorphism

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The Object-Oriented Architectural Style

• Unified Modeling Language (UML) provides building

blocks to describe OO architectures

– Class diagrams

• Define types of components, relationships between

components

– Object diagrams

• Define runtime structure of architecture, showing how classes

are instantiated into objects

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The Object-Oriented Architectural Style

– Sequence diagrams

• Shows timeline of how components

communicate with each other in real scenarios

– Use-Case diagrams

• Show how users interact with system

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Relation Between OO Design and Software Architecture

• Software architecture describes the high-level structure
• f a system in terms of components and connectors
• OO Design (e.g. using UML) can express software

architectures

– Can express not just structure but also dynamic information

• OO Design can also express information at a much lower

level than architecture

– E.g. data structure information