Software Architecture and Style Flashcards by Ashwin Kurup

Software Architecture Definition

Software architecture is considered as a description of the high level structure of a software system in terms of architectural elements and the interactions between them

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what is a Component

 A component is a unit of software that performs some functions at run-time.
 Examples: programs, objects, processes, clients, servers, databases

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What is a connector

Interactions among components:
 communication, coordination, or cooperation among components.

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Examples of Connectors

Examples: shared variable access, procedure calls, remote procedure calls,
communication protocols, data streams, transaction streams.

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Architecture Design Process

 Understand the problem
 Identify design elements and their relationships
 Evaluate the architecture design
 Transform the architecture design

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Key Architecture Principles

Build to change instead of building to last
 Reduce risk and model to analyze
 Use models and visualizations as a
communication and collaboration tool
 Use an incremental and iterative approach

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Key Design Principles 1

Separation of concerns
 Single responsibility principle
 Principle of least knowledge
 Minimize large design upfront
 Do not repeat the functionality

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Key Design Principles 2

Prefer composition over inheritance while reusing the functionality
 Identify components and group them in logical layers
 Define the communication protocol between layers
 Define data format for a layer

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Pipe and Filter architecture Advantages

Concurrency
 Reusability
 Modifiability and low coupling between filters
 Supporting both sequential and parallel execution

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Architecture examples – Pipe and Filter architecture Disadvantages

Disadvantages:
 Low dynamicity
 Overhead

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Process control Architecture description

Data comes from a set of variables, which controls the execution of process
 Processing unit for changing the process control variables and a controller unit for calculating the amount of changes

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A controller unit must have the following elements, for process control architecture:

Controlled variables
 Input variables
 Manipulated variables
 Process definition
 Sensor
 Set point
 Control algorithm
Examples:
 Car-cruise control, anti-lock brakes, temperature
control

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Describe Data-centered architecture

Data is centralized and accessed frequently by
other components, which modify data
 Main purpose: integrity of data
 Components interact only through the data store

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Examples of Data-centered architecture

database architecture, which contains the central data and the data accessor

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The flow of control differentiates the architecture into two sub-categories:

 Repository
 Blackboard

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Repository architecture style:

Data store is passive
 Clients (software components or agents) are
active, which control the logic flow
 Client sends a request to the system to
perform actions
 Computational processes are independent and triggered by incoming requests
look for Repository Architecture image

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Advantages of repository architecture style

Scalability and reusability of agents as they do
not have direct communication with each
other

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DisAdvantages of repository architecture style

Vulnerable to failure
 Changes in data structure highly affect the
clients

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Blackboard architecture style overview

Data store is active and its clients are passive
 Logical flow is determined by the current data
status in data store
 Blackboard component acts as a central data
repository

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Blackboard architecture style Operations

Components act independently on common
data store in the blackboard
 Processing is triggered by the state of the
blackboard

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Blackboard architecture style advantages

 Scalability
 Concurrency

Blackboard architecture style disadvantages

Close dependency exists between blackboard
and agents
 Problems in synchronization of multiple agents

Hierarchical architecture Overview

 Views the whole system as a hierarchy structure
 Software system is decomposed into logical modules

Low-level subsystem give services to its adjacent upper level subsystems, which invoke the methods in the lower level:
 Lower layer – specific functionality
 Middle layer – domain dependent functions
 Upper layer – user interface

Hierarchical architecture sub types, what are they

Three sub-types:
 Main-subroutine
 Master-slave
 Virtual machine

Describe the main subroutine in hierarchical architecture

Main-subroutine  Individual modules or subroutine  Top-down refinement  Functionality may be reused and shared by callers in higher layers See Main-Subroutine image

Main-subroutine Advantages

Main-subroutine Disadvantages

Vulnerable as it contains global shared data  Tight coupling

Master Slave Hierarchical Architecture

Master-slave  Slaves provide duplicate services to the master  Master chooses a particular result among slaves by a certain selection strategy  Slaves may perform the same functional task by different algorithms and methods  Slaves can be executed in parallel See Master Slave Image

Master Slave Advantages

Speed  Robustness  Slaves can be implemented differently

Master Slave Disadvantages

Communication overhead  Not all problems can be divided  Portability issue

What is interaction-oriented architecture

Separate the interaction of user from data abstraction and business data processing  Data module  Control module  View presentation module

What is interaction-oriented architecture sub types

Model-View-Controller (MVC)  Presentation-Abstraction-Control (PAC)

Model-View-Controller (MVC) overview

Model – Manages the data, logic, and constraints of an application  View – output of information  Controller – accepts and input and converts it to commands for the model or view see image

MVC Advantages

Multiple views synchronized with same data model.  Used for application development where graphics expertise, programming, and data base development professionals are working in a team

MVC Disadvantages

Not suitable for agent-oriented applications  Division between the View and Controller is not clear in some cases

is Presentation-Abstraction-Control part of interaction oriented architecture

yes

overview of Presentation-Abstraction-Control

Presentation-Abstraction-Control (PAC) (Hierarchy of many cooperating agents)  Presentation component  Abstraction component  Control component See image Loosely coupled, hierarchical cooperating agents

Presentation-Abstraction-Control Advantages

Support multi-tasking and multi-viewing  Support agent reusability and extensibility

Presentation-Abstraction-Control Disdvantages

Overhead  Difficult to determine the right number of agents

Describe Distributed Architecture

Components are presented on different platforms and several components can cooperate with one another over a communication network in order to achieve a specific objective or goal  Example: ERPS (Enterprise Resource Planning System) See image

Distributed Architecture Advantages

Openness  Concurrency  Scalability  Fault tolerance

Distributed Architecture Disadvantages

 Complexity  Security  Manageability  Unpredictability

Overview of component based architecture

 A component is a modular, portable, replaceable, and reusable set of well-defined functionality that encapsulates its implementation  The decomposition of the design into individual functional or logical components that represent well-defined communication interfaces containing methods, events, and properties  Component reusability

Component-based architecture advantages

Reduced development cost  Increased reliability  Ease of deployment  Reusable  Independent

Component-based architecture Disadvantages

Compromises in requirements may be needed  Less control over the system's evolution

Describe data flow architecture again

Series of transformations to the data Well-defined series of independent data transformations or computations on orderly defined input and output Example:  Compilers  Business data processing

Describe a sub type of data flow architecture, batch sequential

Data transformation subsystem can initiate its process only after its previous subsystem is completely through Example:  Banking application  Utility billing See image

Batch sequential Advantages

Provides simpler divisions on subsystems  Independent programs

Batch sequential Disadvantages

High latency and low throughput  No concurrency and interactive interface

Describe another subtype of data flow architecture, the pipe and filter

see the image it's an incremental transformation

pipe and filter advantages

Concurrency  Reusability  Modifiability and low coupling between filters  Supporting both sequential and parallel execution

pipe and filter disadvantages

Low dynamicity  Overhead