4: A Brief History of Legacy .NET Distributed Technologies in .NET Implement ANSI/AIM Code 128 in .NET 4: A Brief History of Legacy .NET Distributed Technologies

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4: A Brief History of Legacy .NET Distributed Technologies use vs .net code 128a maker togenerate barcode standards 128 in .net WinForms Server-side component .NET code-128c s share and manage pools of database connections alleviating concurrent data access from multiple clients by allowing a single database connection that can accommodate multiple users. A classic distributed architectural model was the 3-tier architecture, where distributed applications were organized into presentation, business, and data tiers, as shown in Figure 4.

2.. thin client business object data access object business object data access object thick client data access object presentation tier business tier data tier Figure 4.2 A typical code128b for .NET 3-tier architecture, separated into the presentation, business, and data tiers.

. The middle business t ier generally contained the bulk of the business logic. Various infrastructure advances, including clustering, helped improve the scalability of business and data tiers, enabling distributed applications to often facilitate hundreds of simultaneous users. The centralization of business logic on the server-side further helped reduce maintenance and versioning effort.

Another benefit to this model was that it made centralized business logic accessible to different types of clients, such as handheld devices and browsers.. 4.1 Distributed Computing 101 Though considered a m ajor advancement in distributed computing, traditional distributed applications still faced some significant challenges: They were often built to automate specific business processes, making them difficult to change when the business process logic changed. They were often difficult to integrate with other applications. Because their distributed architecture exposed multiple access points, convoluted enterprise integration architectures could manifest themselves over time.

They were often difficult to scale to very large user deployments, especially when providing Web access to thousands of potential concurrent users. They were often platform-specific, which could result in vendor lock-in situations..

NOTE One of the origins of distributed computing is RPC (Remote Procedure Calls). In the 1990s, distributed computing moved from procedural programming to object-oriented programming. Remote Method Invocation (RMI) is the object-oriented equivalent of RPC in that it enabled objects on one machine to be accessed by other objects (or applications) running on other machines, by making the remote objects appear local.

Several RMI-like protocols are currently in use, including Java Remote Invocation Call (Java RMI), Common Object Request Broker Architecture (CORBA), and Microsoft s own Distributed Component Object Model (DCOM), which later evolved into .NET Remoting. DCOM essentially extended the original COM model by enabling COM components to communicate across networked computers.

Traditional distributed technologies from Microsoft are covered in the next section.. Service-Oriented Arch .net framework barcode 128a itecture As explained previously in 3, the service-oriented architectural model is a further evolution of traditional distributed architectural models. It is defined via a series of concrete characteristics that allow a given application to be comprised of multiple services that can be repeatedly composed and evolved in response to on-going business change.

. 4: A Brief History of Legacy .NET Distributed Technologies SUMMARY OF KEY POINTS Distributed communi cation protocols are used to enable distributed communication architectures. Computing has moved from procedural programming to object-oriented programming and from object-oriented to service-oriented programming. Communication protocols have evolved with the industry to keep pace with these advancements.

Scalability and performance expectations from a solution have increased over time. Early requirements to scale an application to be used within a small department were easily met by client-server architecture. With the advent of the Internet, solutions were required to scale to thousands of users.

N-tier and peer-to-peer distributed architectures evolved to meet these requirements. Service-oriented architecture takes the benefits provided by distributed architectures further by enabling interoperability and several other benefits explained throughout this book. Microsoft has provided several technologies to enable developing solutions based on distributed architectures.

These technologies include COM, COM+ services, MSMQ, DCOM, .NET Enterprise Services, ASMX (Web services), .NET Remoting, and Web Services Enhancements (WSE).

WCF unifies and replaces these technologies into a single unified programming model.. 4.2 .NET Enterprise Services It All Began with COM (and DCOM) COM helped encapsulate object-oriented systems into binary components. It supported encapsulation by preventing leakage of implementation details, and logic encapsulated in COM components could only be accessed if it had been exposed via a public interface. DCOM extended COM to enable communication across different computers, as shown in Figure 4.

3. DCOM established a secure remote protocol that leverages the security framework provided by the native Windows operating system. For example, it used Access Control Lists (ACL) to secure components that could then be configured using the DCOMCNFG tool.

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