Objective:
In this article we will learn about the Introduction of Middleware and different types of Web services.
Middleware:
It is a connector or a common bridge.
Middleware was first introduced in RPC to Web services.
RPC--------------->Web services
Different types of web services:
- RPC
- CORBA
- COM/DCOM
- RMI
- SOA
- AJAX
- RPC (Remote Procedure Call):
The RPC process starts on the client side. The client application calls a local stub procedure instead of code implementing the procedure. Stubs are compiled and linked with the client application during development. Instead of containing code that implements the remote procedure, the client stub code retrieves the required parameters from the client address space and delivers them to the client runtime library. The client runtime library then translates the parameters as needed into a standard Network Data Representation (NDR) format for transmission to the server.
Marshalling:converting the program language into network portable format.
Problems with distributed system:
- Different operating system
- Different programming language
2. CORBA (Common Object Request Broker Architecture):
- Language Independency
- Platform Independency
IIOP-Internet interoperability protocol
IDL- Interface Definition Language
ORB- Object Request Broker
CORBA 3 is the latest version.
3. COM/DCOM (Component Object Model / Distributed Component Object Model
- Language Independency
- VC++, VB, VB script
It had some flaws because of which DCOM came into existence.
DCOM was a major competitor to CORBA. Proponents of both of these technologies saw them as one day becoming the model for code and service-reuse over the Internet. However, the difficulties involved in getting either of these technologies to work over Internet firewalls, and on unknown and insecure machines, meant that normal HTTP requests in combination with web browsers won out over both of them. Microsoft, at one point, attempted and failed to head this off by adding an extra http transport to DCE/RPC called ncacn_http (Network Computing Architecture connection-oriented protocol). This was later resurrected to support a Microsoft Exchange 2003 connection over HTTP.
DCOM is supported natively in Windows NT 4.0, Windows 2000, Windows XP, and Windows Server 2003, as well as Windows 7, Windows 8, Windows 10, Windows Server 2008, Windows Server 2008 R2, Windows Server 2012, Windows Server 2012 R2 and the Windows Server 2016 Technical Preview.
4. RMI (Remote Method Invocation):
- Platform Independency
Java RMI is shipped with the Java JDK 1.4.
It is a true distributed computing application interface for Java. Unlike other distributed programming interfaces (e.g., Corba, etc.), Java RMI is language specific. This is a good thing because by being language specific, RMI has the ability to provide more advanced feature like serialization, security, etc.
JVM (Java Virtual machine) was launched with RMI.
5. SOA (Service Oriented Architecture):
A service-oriented architecture is essentially a collection of services. These services communicate with each other. The communication can involve either simple data passing or it could involve two or more services coordinating some activity. Some means of connecting services to each other is needed. Service-oriented architectures are not a new thing. The first service-oriented architecture for many people in the past was with the use DCOM or Object Request Brokers (ORBs) based on the CORBA specification. For more on DCOM and CORBA, see Prior Service-Oriented Architectures.
6. AJAX:
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