SOFTWARE ARCHITECTURE:

BASIC CONCEPT

By Xiangzhe Li

Thanh Nguyen

OUTLINE Introduction Terminology

Architecture Component Connector Configuration Architectural Style Architectural Pattern

Model Processes Stakeholders Conclusion

INTRODUCTION

Main idea of this chapter:

Define the key terms & ideas from the field of software architecture.

Provide a uniform basis for their discussion in the remainder of the book.

Architecture

Definition:A software system’s architecture is the

set of principal design decisions made about the system.

The architecture is the blueprint for the construction and evolution of the system.

Architecture (Continue)

Design decisions are involved in every aspect during the construction of the system:

Structure Behavior Interaction Nonfunctional Implementation

Cwm -  data processing software for the semantic web

Principal Definition: Principal implies a degree of importance

that grants a design decision architectural status.

Not all design decisions impact a system’s architecture.

Ex: Algorithm and data structure

Prescriptive vs. Descriptive

Prescriptive architecture represents how the system is intended characteristics and functionalities that are prior to the construction.

Descriptive architecture represents how the system is actually realized after the implementation.

Prescriptive vs. Descriptive (Continue)

Prescriptive architecture is modified during the development of the system due to several factors:

Accommodate actual requirements Code optimization Inadequate techniques and tool support

This leads to ...

Architectural Degradation Architectural drift:Introduction of principal design decisions into a system’s descriptive architecture that - Was not included by the prescriptive

architecture.- Do not violate any of the prescriptive

architecture’s design decisions. Architectural erosion:Introduction of architectural design decisions into a system’s descriptive architecture that violate its prescriptive architecture.

Other Definitions

Perry and WolfArchitecture = {elements, form, rationale}

ANSI/IEEE standard 1471-2000Fundamental organization of a system, embodied in its components, their relationships to each other and the environment, and the principles governing its design and evolution

Chris VerhoefThe software architecture of deployed software is determined by those aspects that are the hardest to change

Component

Definition: An architectural entity that 1) Encapsulates a subset of the system’s

functionality and/or data2) Restricts access to that subset via an

explicitly defined interface3) Has explicitly defined dependencies on its

required execution context

Note: components are usually application specific

Other definition

Clemens SzyperskiA software component is a unit of composition with contractually specified interfaces and explicit context dependencies only. A software component can be deployed independently and is subject to composition by third parties.

Connector

Definition:A software connector is an architectural element tasked with effecting and regulating interactions among components.Examples of connectors: Procedure call connectors Shared memory connectors Distribution connectors

Procedure call connectors

Simplest and widely used type Directly implemented in programming

languages Enable synchronous exchange of data

and control between components Caller to callee relationship

Shared memory connectors

Allow multiple software components to interact by reading from and writing to the shared facilities.

All writers and readers does not depend on each other to perform its tasks.

Distribution connectors

Encapsulate network library application programming interfaces (API)

Enable components in a distributed system to interact

Joined with multiple basic connector to separate the interacting components from the system distribution details

Key Terms

Architecture Design decisions Principal Prescriptive architecture Descriptive architecture Architectural drift Architectural erosion Component Connector