sa4 unit 1.2 design part nh

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WHAT IS SOFTWARE ARCHITECTURE?

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Chapter 2,Chapter 2,Authors: Len Bass, Paul, RickAuthors: Len Bass, Paul, Rick

Page Numbers: 19Page Numbers: 19--4545


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System description of Acoustic Simulation

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What Software Architecture Is and

What It Isn't

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What is the nature of the elements?

What is the significance of separation?

Do they run on separate processors?

Do they run at separate times?

Do the elements consist of processes, programs or both?

Are they objects, task, functions, processes, distributed programs,

What are the responsibilities of the elements?

What is it they do?

What is their function in the system?

What is the significance of the connections?

Do the connections mean that the elements communicate with each other , control each other , send datato each other , use each other, invoke each other, share some information hiding secret with each other,

What information flows across the mechanism? What is the significance of the layout?

Why is CP on a separate level?

Does it call the other three?

Are others not allowed to call?


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Architecture: Definition

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The Software Architectureis a structure orstructures of the system, which comprise

software elements, the externally visible

properties of those elements, and the

relationships between them


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Architecture Definition

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externally visible properties -

assumptions other elements can make of an

element, such as its provided services,

performance characteristics, fault handling,

shared resources usage


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Architecture: Definition observation

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Architecture defines software elements

embody The architecture represents information about how the elements

relate to each other

An architecture is foremost an abstraction of a system thatsuppresses details of elements that do not affect how they use,are used by, relate to, or interact with other elements.

Architecture is concerned with the public side of this division


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Systems can and do comprise more than one structure

All nontrivial projects are partitioned into implementation units;

these units are given specific responsibilities and arefrequently the basis of work assignments for programming

teams.


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Every computing system with software has a software architecture

Every system can be shown to comprise elements and the relations among them.

Unfortunately, an architecture can exist independently of its description or

specification, which raises the importance of architecture documentation and

architecture reconstruction


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the behavior of each element is part of the

architecture

behavior can be observed from the point of view of

another element.


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the definition is indifferent as to whether the

architecture for a system is a good one or a bad

one

meaning that it will allow or prevent the system

from meeting its behavioral, performance, and life-

cycle requirements.

We do not accept trial and error as the best way tochoose an architecture for a system


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Other Points of View

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Architecture is high-level design

Architecture is the overall structure of the system

Architecture is the structure of the components of aprogram or system, their interrelationships, and theprinciples and guidelines governing their design andevolution over time

Architecture is components and connectors


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An architectural pattern is a description of element

and relation types together with a set of

constraints on how they may be used

Set of constraints on an architecture

Example-C/S architecture.

Architectural PatternsArchitectural Patterns


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Reference Models

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A reference model is a division of functionality

together with data flow between the pieces.

It is standard decomposition of a known problem into

parts that solves problem cooperatively

Ex: OSI reference model..


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Reference Architectures

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A reference architecture is a reference model

mapped onto software elements (that cooperatively

implement the functionality defined in the reference

model) and the data flows between them

----

Reference model divides the functionality.

A reference architecture is the mapping of thatfunctionality on to a system decomposition


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Architecture: useful concepts

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ReferenceReferencearchitecturearchitecture

SoftwareSoftwarearchitecturearchitecture

ArchitecturalArchitecturalpatternpattern

ReferenceReferencemodelmodel


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Why is Software Architecture Important?

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1. Communication among stakeholders

-used as a basis for mutual understanding,

negotiation, compromise, and communication.


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2. Early design decisions

Architecture represents earliest set of decisions

about system, they are most difficult to get correct

and the hardest to change the earliest point at

which design decisions can be analyzed


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3. Transferable abstractions of a system

Architecture is a relatively small model for how a

system is structured and how its elements work together

and this is transferable across systems.


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Each stakeholder of a software system is concerned

with different system characteristics that are

affected by the architecture.

Architecture provides a common language in which

different concerns can be expressed, negotiated,and resolved at a level that is intellectually

manageable even for large, complex systems

ARCHITECTUREIS THE VEHICLE FOR STAKEHOLDERARCHITECTUREIS THE VEHICLE FOR STAKEHOLDERCOMMUNICATIONCOMMUNICATION


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ARCHITECTURE MANIFESTS THEEARLIEST SET OF DESIGN

DECISIONS

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Software architecture represents a system's earliest

set of design decisions.

These early decisions are the most difficult to get

correct and the hardest to change later in the

development process, and they have the most far-reaching effects.


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ARCHITECTURE MANIFESTS THE EARLIEST SET OF

DESIGN DECISIONS contd

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The Architecture Defines Constraints on Implementation

The Architecture Dictates Organizational Structure

The Architecture Inhibits or Enables a System's Quality Attributes

Performance, Modifiability, Security, Scalability, Reusability

Predicting System Qualities by Studying the Architecture

The Architecture Makes It Easier to Reason about and Manage Change

The ArchitectureHelps in Evolutionary Prototyping

The Architecture Enables More Accurate Cost and Schedule Estimates


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ARCHITECTURE AS A TRANSFERABLE, RE-USABLE MODEL

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The earlier in the life cycle re-use is applied, the

greater the benefit that can be achieved

When architectural decisions can be re-used across

multiple systems, all of the early decision

consequences we just described are alsotransferred.


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ARCHITECTURE AS A TRANSFERABLE, RE-USABLE

MODEL contd..

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Software Product Lines Share a Common

Architecture

Systems Can Be Built Using Large, Externally

Developed Elements

Less Is More: It Pays to Restrict the Vocabulary of

Design Alternatives

An Architecture Permits Template-BasedDevelopment

An Architecture Can Be the Basis for Training


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Architectural Structures and Views

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A structure is the set of elements structure-set ofelements.

view It is a representation of logical set ofarchitecture elements, as written by and read bysystem stakeholder.

It consist of representation of a set of elements andthe relations among them


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Architectural StructuresArchitectural Structures

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- module structuresbasic elements are modules, they are assigned areas of

functional responsibility, less emphasis on runtime issues

- component-and-connector structures

elements are run-time components (units of computation) and connectors

(communication vehicles)

- allocation structuresshows the relationship between the software elements and theelements in one or more external environments in which softwareis created and executed


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Architectural Structures: Module

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modulemodule

decompositiondecomposition usesuses classclass

layeredlayered


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Architectural Structures: Component-and-Connector

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componentcomponent--andand--connectorconnector

clientclient--serverserver

processprocess

shared datashared data

concurrencyconcurrency


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Architectural Structures: Allocation

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allocationallocation

Work assignmentWork assignment implementationimplementation

deploymentdeployment


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Architectural Structures: Module

Softwarestructure

Relations Useful For Reason About

decomposition is a submodule, sharessecrets with

resource allocation, project structuringand planning, information hiding,

encapsulation, configuration control

Uses requires the correct presence of

extension or extraction of functionality

layered requires the correct presence of, uses theservices of, providesabstraction to

incremental development,implementing systems on top of

virtual machines

class is an instance of, sharesaccess methods of

in OO producing rapid almost-alikeimplementations from a commontemplate

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Architectural Structures: Component-Connector

Software

structure

Relations Useful For Reason About

client-server communicates with,

depends on

distributed operation,separation of concerns,

performance, loadbalancing

process runs concurrently with, may runconcurrently with, excludes, precedes

scheduling, performance

concurrency runs on the same logical thread locations where resource

contention exists, wherethreads may fork, join,be created or killed

shared data produces data, consumes data performance, dataintegrity, modifiability


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Architectural Structures: Allocation

Software structure Relations Useful For Reason About

deployment allocated to,migrated to performance, availability,security

implementation stored in configuration control,integration, test activities

work assignment assigned to project management,

best use of expertise,management ofcommonality


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Architectural Structures: which one to choose

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Philippe Krutchten (1995): four plus one approach

1. Logical : Elements are key abstractions.

This is module structure.

2. Process : Addresses concurrency and distribution of functionalityIt is a component-and-connector structure.

3. Development : This shows the organization of software modules, libraries,

subsystems, and units of development.

- It is allocation structure.

4. Physical : This maps other elements onto processing and communication

nodes.

It is an allocation structure.

sa4 unit 1.2 design part nh

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