sa unit 1 chapter 2 software architecture

8/12/2019 Sa Unit 1 Chapter 2 Software Architecture

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What is Software Architecture?


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System description of Acoustic Simulation


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What Software Architecture Is and

What It Isn't 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 data to each other , use each other, invoke each other, share some information hidingsecret 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

The Software Architecture is a structure

or structures of the system, which

comprise software elements, the

externally visible properties of those

elements, and the relationships betweenthem


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Architecture Definition

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: Definitionobservation

Architecture defines software elements

The architecture represents information about how theelements 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.


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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 to choose an architecture for a system


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Other Points of View

Architecture is high-level design

Architecture is the overall structure of the system

Architecture is the structure of the componentsof a program or system, their interrelationships,

and the principles and guidelines governing theirdesign and evolution 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 Patterns


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Reference Models

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

A reference architecture is a reference model

mapped onto software elements (that

cooperatively implement the functionalitydefined in the reference model) and the data

flows between them

Reference model divides the functionality.

A reference architecture is the mapping of that

functionality on to a system decomposition.


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Architecture: useful concepts

Referencearchitecture

Softwarearchitecture

Architecturalpattern

Referencemodel


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Why is Software Architecture Important?

1. Communication among stakeholders

-SA represents a common abstraction of a system.

-used as a basis for mutual understanding,negotiation, compromise, and communication

by the stakeholders.


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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.

It is 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.

It can be applied to other systems exhibiting

similar functional requirements.


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Each stakeholder of a software system (customer,user, project, manager, coder, tester) isconcerned with different system characteristicsthat are affected by the architecture.

User is concerned that system is reliable &available.

Customer is concerned about schedule & budget.Manager: teams should work independently.

Architect: worried about strategies to achievegoals.

ARCHITECTURE IS THE VEHICLE FOR STAKEHOLDERCOMMUNICATION


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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


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Architecture manifests the earliest set of design

decisions

Constraints on implementation

Dictates organizational structure

Inhibits or enable quality attributes

Predicting system qualities

Easier to reason about and manage change

Evolutionary prototyping

Accurate cost and schedule estimates


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Architecture as transferable re-usable model

Software Product lines share a common

architecture

Systems can be built using large, externally

developed elements

Less is more

Template based development

Basis for training


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Architectural Structures and Views

A structure is the set of elements.

view It is a representation of set ofarchitecture elements, as written by and readby system stakeholder.

It consist of representation of a set ofelements and the relations among them


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Architectural Structures

- module structuresbasic elements are modules.

they are assigned areas of functional responsibility.

Module allow us answer

What is the primary responsibility of module?What other software does it use?


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- component-and-connector structures

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

connectors (communication vehicles).

What are the major components & how do they interact?How does data progress through the system?

- allocation structures

shows the relationship between the software elements and theelements in external environment in which software is

created and executed

What is the assignment of S/W elements to development team


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Architectural Structures: Module

module

decomposition uses class

layered


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Architectural Structures: Component-and-

Connector

component-and-connector

client-server

process

shared data

concurrency


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Architectural Structures: Allocation

allocation

Work assignment implementation

deployment


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Decomposition:

Units are modules related to each other by is a sub module of relation.

Shows how larger modules are decomposed into smaller modules

recursively till the smaller modules are easily understood.

Modules have associated products (code, test plans). Provides modifiability, by ensuring that changes to small modules.

Used for project structuring also for integration & test plans.

Uses :

Structure are modules or procedures.

Relation is uses.

One unit uses another if the correctness of the first requires the presence

of a correct version of second.


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Layered:

If the Uses relation is carefully controlled the a system of layer comes in

picture.

If there are n layers. Then the nth layer will use only service from layer n-1.

Layers are often designed as abstractions & hide implementation specificsbelow from the layers above.

Class:

module units are called classes

Relation is inherts- from

Collection of similar behavior.

This allows us to reason about reuse and additional functionality.


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Architectural Structures: Component-and-Connector

Process or communicating processes:

Deals with dynamic aspects of a running system.

Units here are processes or threads which communicate, synchronize with

each other.

The relation is attachment how components and connecters are linkedtogether.

Concurrency:

Allows the architects to determine the opportunities for parallelism.

Units are components and connecters are logical threads

Logical thread is a sequence of computation, that can be allocated to a

separate physical thread in design process.


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Shared data or repository:

The structure comprises components and connecters that create, storeand access data

It shows how data is produced and consumed by run time softwareelement.

It is used for good performance and data integrity.

Client and server:

Built as a group of cooperating clients and servers.

Components are clients and servers & Connecters are protocols and

messages

Used for load balancing( supporting run time performance) and physicaldistribution.


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Deployment: Shows how software is assigned to hardware processing and

communication elements.

The elements are software, hardware, and communication pathways.

Relations are allocated to (shows which physical units are assigns to

software elements), and migrates to (if allocation is dynamic)

Helps to understand the performance ,availability, security.

Implementation:

shows how software elements are mapped to file structures in thesystems development, integration.

This is critical for management of development activities.


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Work assignment:

This structure assigns responsibility for implementing and integrating the

modules to appropriate development teams.

This structure which is the part of the architecture makes it clear about

the decisions who does the work.

The architect will know the expertise required on each team.


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Softwarestructure Relations Useful For Reason About

Decomposition is a sub module, sharessecrets with

resource allocation, project structuringand planning, information hiding,

encapsulation, configuration control

Uses requires the correctpresence of extension or extraction of functionality

layered requires the correctpresence of, uses thervices of, providesabstraction to

incremental development,implementing systems on top ofvirtual machines

Class is an instance of, sharesaccess methods of

in OOproducing 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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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

sa unit 1 chapter 2 software architecture

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