OO Methodology OO Architecture

Table of Contents Definition of Software Architecture Architecture Dimensions and Views Architectural Patterns Architectural Pattern: Layers Partial Logical View of NextGen POS Inter-Layer and Inter-Package Dependency Inter-Layer and Inter-Package Interaction Packages vs Subsystems Session Facades and Application Layer Logical vs Process and Deployment Views Implementation View Deployment View

Definition of Software Architecture RUP definition of architecture is The organization of a software system The selection of structural elements and their interfaces by which the system is composes, together with their behavior as specified in the collaboration among those elements The composition of these elements into progressively larger subsystems The architectural style that guides this organization, these elements and their interfaces, their collaboration, and their composition Buschmann et al. A software architecture is a description of the subsystems and components of a software system and the relationships between them. Subsystems and components are typically specified in different views to show the relevant functional and nonfunctional properties of a software system. The software architecture is the result of the software design activity

Architecture Dimensions and Views The 4+1 View Model of Architecture (P. Kruchten95) The Logical View addresses the functional requirements of the system an abstraction of design model UML package, class and interaction diagrams The Implementation View describes the organization of static software modules(source code, data files, components, executables etc.) UML package and component diagrams The Process View addresses the concurrent aspects of the system at runtime, task, threads or processes as well as their interactions. allocation of logical elements to them UML class and interaction diagrams Logical View Implementation Process Deployment Use-Case

Architecture Dimensions and Views Deployment View addresses physical deployment of processes and components to processing nodes and the network configuration between nodes UML deployment diagrams Use Case View describes the most architecturally significant use cases and their non-functional requirements. UML use case diagrams Models and Views A model is a complete representation of the system (at least in one aspect) Architectural views focuses only on what is architecturally significant. “not all design is architecture” Architectural views are like slices cut through the various models, illuminating only the important, significant elements of the models. Architecturally significant elements has a wide impact on the structure of the system and on its performance, robustness, and scalability etc. major use cases major classes architectural mechanisms patterns and frameworks major processes or threads etc.

Architectural Patterns Three types of Patterns [Buschmann et.al. 1996] Architectural styles Design Patterns Idioms Architectural Styles related to the large-scale and coarse-grained design typically applied when the major structures and connections are established expresses a fundamental structural organization schema for software system Example: Layers Pipes and Filters Blackboard Broker MVC related to the small and medium-scale design of objects and frameworks Example: Singleton, Proxy, Command, Adapter, Facade, Strategy etc. language or implementation-oriented low-level design solutions Example: Canonical forms, Java maxim

Architectural Pattern: Layers Layer pattern organize the large-scale logical structure of a system into discrete layers of distinct, related responsibilities with a clean, cohesive separation of concerns

Partial Logical View of NextGen POS

Inter-Layer and Inter-Package Dependency

Inter-Layer and Inter-Package Dependency

Inter-Layer and Inter-Package Interaction To understand the dynamics of how objects across the layers connect and communicate Illustrate architecturally significant scenarios Emphasizes cross-boundary connections

Packages vs Subsystems is a coherent piece of a system that can be treated as an abstract single unit can be modeled both as a package and as a class has a behavior and a set of interfaces Facade a subsystem provides a public facade object outside the subsystem a facade object for a entire system system-wide facade vs session facade

Session Facades and Application Layer application layer contains objects responsible for knowing the session state of clients, mediating between the presentation and domain layers When multiple user interfaces will be used When in a distributed system, domain layer is on a different node than presentation layer and shared by multiple clients When there is a defined workflow in terms of the controlled order of windows or web pages that must be presented

Upward Collaboration with Observer Observer pattern is used for domain objects to communicate upward with the presentation layer, where as Facade pattern is used for downward collaboration

Logical vs Process and Deployment Views The architectural layers are a logical view of the architecture, not a deployment view of elements to processes and processing nodes There are many ways to slice and dice these logical layers for deployment depending on the platform

<<database>> Physical Views Physical views include Implementation view Deployment view Implementation View models the components in a system, that is, software units from which the application is constructed, as well as their dependencies models the assignment of classes and other model elements to components displayed on component diagrams <<database>> TicketDB CreditCardCharges status charge purchase groupSales TicketSeller ManageInterface indivisualSales subscriptionSales KioskInterface ClerkInterface

<<database>> Physical Views Deployment View depicts the run-time architecture of processors, devices and the software components that execute in this architecture physical description of the system topology, describing the structure of the hardware units and the software that execute on each unit represents the arrangement of run-time component instances and/or objects on node instances 1 CreditCardCharges ManageInterface TicketSeller <<database>> TicketDB TicketServer 1 1 * * KioskInterface ClerkInterface Kiosk SalesTerminal