Figure 6-7 A layered architecture in UML in Java

Create QR Code JIS X 0510 in Java Figure 6-7 A layered architecture in UML
Figure 6-7 A layered architecture in UML
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Tiers
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Tiers are primarily concerned with distribution of a software system over mul tiple, separate processes Processes may be physically distributed over multiple processors or reside on the same physical device
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Tiers can be mapped to responsibility-driven layers in which case a tier becomes synonymous with fulfilling a specific role within the system, such as presentation, business logic, data access, and so on
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Mainstream computing has evolved over time into the multitiered architectures in use today In the early days of computing, mainframes and dumb terminals characterized the computing environment Two-tiered, LAN-based client-server systems were the norm for a long time And although n -tier architectures have been utilized in specific industries for a long time, it is only recently that n -tier architectures are becoming mainstream in the industry
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Tiered architectures are desirable from the point of view of increasing throughput, availability, or functionality of the system by increasing the overall, physical processing power Tiered architectures can also play a role in separating out different areas of application concerns to improve overall maintainability
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Such distribution introduces
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Communication efficiency and reliability issues between tiers The need for identification and location of components in a distributed environment Security issues due to a potentially diverse and geographically d istributed system Synchronization issues between tiers Failure recovery issues The need for additional interfaces to accommodate the tier architecture Additional resource needs due to the distributed nature of the software
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As discussed earlier, one way to achieve distribution in an n -tier architecture is to align specific layers with each tier J2EE follows this approach
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In the J2EE tiered architecture:
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Client tier is primarily concerned with user interaction
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Presentation tier deals with presenting the re sults of business queries Business tier contains the key business rules Data tier provides the interface to the persistent data store
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The J2EE approach is shown graphically in Figure 6 - 8
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Figure 6-8 J2EE tiers
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Approaches to Software Architecture
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Numerous approaches to software architecture have been proposed and utilized over time In this section, we highlight some published approaches to software architecture to provide you with a broader perspective
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Each of these approaches has its strong points and weaknesses as well as its advocates and critics
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The J2EE View of Architecture
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Tiers + components + services are key to understanding the J2EE architectural philosophy
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Given that the J2EE is predominantly focused on providing a viable proposit ion for building large-scale enterprise applications that are scalable, it should come as no surprise that it advocates partitioning the application into multiple tiers The J2EE platform provides mechanisms to decompose the system into relatively coarse-grained components J2EE also advocates a services-based architecture that is characterized by a collection of cooperating and communicating services The services rely on well-defined APIs for interoperability
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The J2EE official guidelines shy away from a strict recommendation of adherence to a layer-like hierarchical view of the tiers, opting instead for a more accommodating stance The suggestion is to use the tiers and associated technologies if it makes sense for the specific situation For example, it is perfectly appropriate to access the data tier directly from the presentation tier
J2EE recommends using the Model-View-Controller (MVC)[3] architectural paradigm for developing enterprise applications As discussed briefly in 2 , the basic idea behind the MVC is to minimize the coupling among objects in a system by aligning them with a specific set of responsibilities in the area of the persistent data and associated rules (Model), presentation (View), and the application logic (Controller)
For more details and the J2EE perspective on the MVC paradigm, see
javasuncom/j2ee/blueprints/design_patterns/model_view_controller/indexhtml Additional sources are listed in the References section at the end of this book
The 4+1 View Model of Architecture
The primary motivation behind using different views for architecture is to reduce the overall complexity
A view is essentially a look at the model from a specific vantage point or perspective, such that only the details that are relevant and important are included and all else is ignored
Originally proposed as the 4+1 View Model of Architecture [Kruchten 1995 ], it is now part of the RUP It has been widely used as the basis for architectural analysis and design of systems
The basic premise behind the 4+1 View of Model Architecture is that a software system can be modeled well with the following interlocking views:
The Logical View models design packages, subsystems, and classes The Implementation View describes the physical organization of the software, for example, executables, libraries, source code, and so on
The Process View is concerned with the concurrency aspects of the software For example, processes, tasks, and threads that are part of the software system
The Deployment View focuses on the mapping of the executables onto physical nodes and computing hardware