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Executional Architecture

Lecture 16-19

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Conceptual vs execution

ConceptualArchitecture

ExecutionArchitecture

Component

Connector

Domain-level responsibilities

Concurrent activity

Flow of information

Invocation relationship

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Execution view

Focuses on the system runtime structure, as:

Hardware elements, subsystems, processes and threads

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Execution view

Suited for examining quality attributes, most-notably runtime attributes e.g. performance, scalability, etc

Comprised of “components and connectors”

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Components in execution architecture

Concurrent components are designed by: “abstraction created by execution of a

software program”

If the system is a single-computer, single-process, single-thread system then the execution architecture is very simple; having just one runtime entity.

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Components in execution architecture Thus, execution architecture is needed for:

1. Distributed systems, Network-based systems

2. Concurrent systems Multi-processor systems (multi-core) Multi-threaded systems - GUI systems

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Components in execution architecture

Hardware: runtime resources, Shared memory… e.t.c

Concurrent subsystems: typically has a dedicated computer that runs

it. Processes:

runs on a single computer and has its own memory space.

Threads: executes concurrently with other threads

within the memory space of a parent process.

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Connectors in execution architecture Connectors indicate that one component calls

another The arrow depicts the call direction The arrowhead points from the calling

component to the called component

Three different types of arrows for three different calling scenarios: Synchronous Asynchronous Callback

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Connectors in execution architecture Synchronous communication:

the calling components waits for a response of the called component

Asynchronous communication: the calling component does not wait for a

response

Callback: The calling component receives a response

asynchronously by setting a means by which the called component can send response later

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Communication

Arrows indicate an invocation relationship;

Asynchronous call

Synchronous call

Callback

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Execution stereotypes

Similarly to conceptual components execution components can belong to stereotypes

We will use three different stereotypes

Each stereotype has a particular clearly defined semantics

In execution architecture this semantics describes the kind of concurrent activity

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Activity stereotypes

User-initiated

Active

Service

How is concurrent activity initiated?

By user action

By an active thread or threads of control

In response to a request

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Execution stereotypes

User-initiated: “the component performs action because of

user input”

This components are always user-interfaces.

E.g. an event thread that listens to user-input events, enhances responsiveness of user-interface, and in general usability

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Execution stereotypes Active:

“the component generates activity internally”

Typical for real-time portions of the system

For example:1. Components loop continuously or wake up

periodically 2. A crawler in a search engine might be an active

component Whenever there is a new page it generates activity and

invokes parser, analyzer, indexer, ...

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Execution stereotypes Services:

“the component waits for requests of other components and generates responses for such requests”

Typically performs a complex task and has

clearly defined protocol for communication with other components

E.g. database, web, file servers

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Concurrent subsystems view Contains only concurrent subsystems The highest-level execution view of the

system

A simple audio processing system

Audio Capture/ Playback

SoundLibrary

Sound UI

Audio In/Out

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Execution Architecture Design In Execution Architecture Design, we design a

number of different models: Some of them will include physical

components: i.e. hardware

Each model is a model at a specific level of Detail: Less details: concurrent subsystems,

processes More details: threads

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Concurrent subsystems model

Top-level execution model: To get an overview of the running system.

Detail-level execution model: Overview of the running system and its

concurrent subsystems. Subsystems can be quite complex and have

many processes and/or threads. However, a concurrent subsystem is not

something that is clearly defined in many cases.

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Concurrent subsystems model

A process that has a high degree of internal concurrency (threads) should be treated as a concurrent subsystem.

E.g. a server is typically a single process but might create threads to handle client requests.

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Concurrent subsystems model

A concurrent subsystem is always long-lived:

Created when the systems is started

Operates throughout the system lifetime

Closed when the system is shutdown

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Process model

Basically, you examine each concurrent subsystem for processes.

Restricting a concurrency model to processes depicts the execution structure.

You do not go into details on external system.

Typically, such models will be only slightly more detailed than concurrent subsystem mode.

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Process model (2)

Process model of a TCP/IP server

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MPS Execution Architecture Start with the big picture: concurrent systems:

MPS is a Web application What concurrent subsystems will we have:

1. A Web browser and a Web server:a. The application logic is on the server side b. We need a Web server which can run

applications

2. Thus, the Web server is actually a Web application server

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MPS Execution architecture

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Detailed execution model Includes process‘s threads, but;

Threads do not have their own memory space Nor they have their own copy of the code in

memory

The code is loaded only once by their parent process

The memory is typically shared by the threads

We need to take care about thread synchronization

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MPS Detailed Execution Architecture Example: Web server with a database server

A content management system(CMS) with content stored in a database

What happens when a field is updated in the database? Note, Database server is a separate process

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MPS Detailed Execution Architecture

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Quality attributes Many quality attributes are addressed by the

execution architecture: For example:

Usability: in GUIs is addressed by a special event thread

Highly Reliability: component needs a separate execution component

Security: typically requires a separate execution component

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Execution behavior

We will use-case maps to model behavior

Actually we need only to verify that execution architecture supports the desired behavior.

We can use the same use-case maps from the conceptual architecture.

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Execution arch. summary What you need to submit:1. Execution diagram showing where

conceptual components reside.2. Execution diagram using stereotypes.3. The same use-case maps from conceptual

architecture as a verification of execution architecture.

4. If needed some textual explanation to backup your decisions.