Web services & com+ components

Web services & com+ components

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  BY G.GOWRILATHA,M.Sc(Info Tech) Department OfCS & IT Nadar Saraswathi College Of Arts and Science, Theni.
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  WEB SERVICES : Webservice is simply an application that exposes a Web-accessible API. That means you can invoke this application programmatically over the Web. XML+HTTP =SOAP (Simple Object Access protocol) :  Web services allow applications to share data. Web services can be called across platforms and operating systems regardless of programming language.  .NET is Microsoft's platform for XML Web services. Using SOAP you can invoke the Web Series. (HTTP-GET, HTTP- POST, SOAP) .  SOAP -Simple Object Access protocol is message-based protocol. Based on Request and Response. Here I am not going to explain more details about SOAP.
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   Like Payper view Channel we can make Software as pay per use, using Web service. For example, let say Info vision Inc developed Expensive Software for 3D Virtual Modeling. Lot of company does not want acquire the licensee because it is expensive and they need to pay for Support etc. Instead of this if Info vision makes this software as a Web Service, most of the company will use as pay per use.  Using VisualStudio.NET we can easily create Web Services. ASP.NET Web Service this project type will be used to create Web Service.
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  COM+ Component Services: The .NET Framework leverages many existing Windows services to make it a more robust application environment. A particular technology that deserves attention is COM+ Component Services.  These technologies were the predecessors to the .NET Framework. To see how COM+ Component Services fits into the .NET Framework arena, let's explore a little about these technologies. Overview of COM:  The Component Object Model (COM) was designed to address the shortcomings of conventional object-oriented languages like C++ and traditional binary software distribution of code. COM is about not a particular type of software but rather a philosophy of programming.
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   This philosophyis manifested in the COM specification. The specification explicitly states how a COM object should be constructed and what behaviors it should have.  COM objects are roughly equivalent to normal classes, but COM defines how these objects interact with other programs at the binary level. By binary, I mean compiled code, with all the methods and member variables of the class already built into an object. COM was the first methodology to address object-oriented software reuse. COM has enjoyed great commercial success; many third-party software vendors provide COM objects to perform a wide range of tasks, from e-mail to image processing.
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   COM isalso highly useful for creating components called business objects.  Business objects are COM objects in the strict sense, but they are used to encapsulate business rules and logic. Typically these business objects are tied to database tables. The objects move around the database according to the business rules implemented in the COM object. Overview of Transactions:  Atomicity means that either the operation that the component performs is completely successful or the data that the component operates on does not change at all.  This is important because if the transaction has to update multiple data items, you do not want to leave it with erroneous values.
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  A classic exampleof a transaction operation is a bank transfer that involves a transfer of funds from one account to another (a credit and a debit). Such a transaction moves through the following steps. 1.Get the amount to be transferred, and check the source account for sufficient funds. 2.Deduct the transfer amount from the source account. 3.Get the balance of the destination account, and add the amount to be transferred to the balance. 4.Update the destination account with the new balance. Each of the account transfer's steps can be checked for success or failure. If every step succeeds, the program needs to apply all the changes made to the database. That's when a commit operation is performed.
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  Automatic Transactions: Transactions havebeen in widespread use since the early days of enterprise computing. Many database systems include internal support for transactions. Such database systems contain native commands to begin, abort, and commit transactions. Automatic transactions differ from manual transactions because automatic transactions are controlled by a system external to the database management system (DBMS). Earlier versions of Windows (95/98/NT) provide automatic transaction services using Microsoft Transaction Server (MTS).  MTS works by coordinating database updates made by COM components grouped into a logical unit called a package. An MTS package defines the boundary of the transaction. Each component in the package participates in the transaction.
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  MTS then makesa determination to continue based on the success of the last component's signal of success or failure. If the transaction step was unsuccessful, the transaction is aborted immediately, and MTS instructs the DBMS to undo any changes made to data. COM+ Applications COM+ also offers performance improvements over MTS by implementing technologies such as object pooling, which maintains an active set of COM component instances. Other performance-enhancing features include load balancing, which distributes component instances over multiple servers, and queued components, which uses Microsoft Message Queue Server to handle requests for COM+ components.
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   The servicesthat were formerly provided by MTS are known as COM+ Component Services in the COM+ model. COM+ Component Services works in a similar manner to MTS. Packages are now referred to as COM+ applications. Participating transactional components are grouped into applications in the same way components were grouped into packages under MTS.  Individual COM+ components in an application can be assigned different levels of involvement in an automatic transaction. When setting up COM+ applications, each component can have the levels of automatic transaction support
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  Transaction Support Description Disabled-No transaction services are ever loaded by COM+ Component Services. Not Supported -This is the default setting for new MTS components. Execution of the component is always outside a transaction regardless of whether or not a transaction has been initiated for the component. Supported -You may run the component inside or outside a transaction without any ill effects. Required The component must run inside a transaction. Required New -The component needs its own transaction in which to run. If the component is not called from within a transaction, a new transaction is automatically created.
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  COM+ Security:  Securityis of paramount importance, especially for applications intended to run on the Internet. In the past, programming security features into an Internet application was largely a manual effort. Often it consisted of custom security schemes that did not necessarily leverage the existing security infrastructure provided by the operating system. COM+ Component Services provides a security infrastructure for applications that uses Windows 2000/XP users and groups. COM+ security is declarative, which means you designate which users and groups have permission to access a COM+ application. This is done by defining roles for application access.
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  . NET Classesand COM+ Component Services:  COM+ Component Services, transactions, and security deal specifically with COM+ components. COM+ predated the .NET Framework and has had much success in enterprise-wide applications developed using Microsoft Visual Studio 6.0.  COM+ still remains a dominant technology and is a significant part of Windows. The architecture for .NET managed components was designed to take advantage of all the features COM+ Component Services has to offer (object pooling, transaction processing, security, and so on) by providing classes to implement those features.
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  Thank You!