Middleware Zongrui Li Candido Gomez Peter Tran Jose Villar

Content: Introduction Remote Procedure Call (RPC) Message-Oriented Middleware (MOM), Transaction processing (TP) monitors Conclusion Key Words References

What is the Middleware? Middleware is connectivity software that consists of a set of enabling services that allow multiple processes running on one or more machines to interact across a network.

History Middleware first appeared in the late 1980s to represent network connection management software. Until the mid 1990s, it was general recognized, when network technology had accomplished sufficient access to it. Remote Procedure Call (RPC) was the first communication-based middleware, which was first developed by circa 1982 by Birrell and Nelson.

What are the benefits of middleware? Simplicity: Putting middleware in the middle can mean each application needs only one interface—to the middleware—instead of a separate interface to each application it needs to talk to. Persistence: Middleware can capture data and hold on to it until it has been recorded appropriately by all the applications or databases that need the information. Services: If your data needs to be checked for integrity, printed out, reconciled with data from other applications, merged, split or reformatted, various kinds of middleware can handle those tasks efficiently.

Middleware can take on the following different forms: Remote Procedure Call (RPC) system, which enable the logic of an application to be distributed across the network. Program logic on remote systems can be executed as simply as calling a local routine. Message-Oriented Middleware (MOM), which is a specific class of middleware that supports the exchange of general-purpose messages in a distributed application environment.

Continue: Transaction processing (TP) monitors, which provide tools and an environment for developing and deploying distributed applications. Object Request Brokers (ORBs), which enable the objects that comprise an application to be distributed and shared across varied networks.

Remote Procedure CallRemote Procedure Call (RPC)

Origin Sun Microsystems developed the first widely used RPC protocol as part of their Open Network Computing (ONC) it was develop in the early 1980s. The specification has been handed off to the Internet Engineering Task Force (IETF) as a step toward making ONC RPC an Internet standard.

What is RPC? Remote Procedure Call (RPC) is a client/serverRemote Procedure Call (RPC) is a protocol that one program can use to request a service from a program located in another computer in a network without having to understand network details.

How does it work? The requesting program is a client and the service- providing program is the server. Like a regular or local procedure call, an RPC is a synchronous( from Greek syn-, meaning "with," and chronos, meaning "time") operation requiring the requesting program to be suspended until the results of the remote procedure are returned.

However, the use of lightweight processes that share the same address space allows multiple RPCs to be performed concurrently. Client Server Requesting Programservice-providing program router

When program statements that use RPC are compiled into an executable program, a stub is included in the compiled code that acts as the representative of the remote procedure code.

What is a stub? A stub is a small program routine that substitutes for a longer program For example, a program that uses Remote Procedure Calls (RPC) is compiled with stubs that substitute for the program that provides a requested procedure.

When the program is run and the procedure call is issued, the stub receives the request and forwards it to a client runtime program in the local computer. The client runtime program has the knowledge of how to address the remote computer and server application and sends the message across the network that requests the remote procedure.

How it is performed? The network needs to be made invisible, so that everything looks just like ordinary procedure calls. All networking should be done by the RPC implementation, such as connecting to the remote machine. On the remote machine this simple function gets executed:

int remote_time(char *time_buf) { struct tm *time; time_t t; time(&t); time = localtime(&t); strcpy(time_buf, asctime(time)); return 0; }

Tools are available for a programmer to use in developing RPC applications over a wide variety of platforms, including Windows (3.1, NT, 95), Macintosh, 26 variants of UNIX, OS/2, NetWare, and VMS

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Summary RPC is a protocol which allows a program running on one host to cause code to be executed on another host without the programmer needing to explicitly the code. RPC is an easy and popular paradigm for implementing the client-server model. An RPC is initiated by the caller (client) sending request message to a remote system (the server) to execute a certain procedure using arguments supplied. A result message is returned to the caller.

What is MOM? 1.Mediator for messages (Broker) 2.Asynchronous communcation architecture CORBA Messaging (MOM) 2.ORB takes functions from MOM (MOB) 3.no standard

Why do you need a Message-oriented Broker (MOB) ? 1.Accessing to remote data and processes through an internet or intranet 2.Building applications involving multiple servers and clients 3.Simultaneous acces to heterogeneous information (RDBMS, ODBMS, Legacy DB) 4.Decoupling of Client and Server

Types of MOM Message Passing (PtP) direct communication connection oriented synchronous transfer asynchronous transfer (callback) Message Queuing (MQ) indirect communication over message queuing connectionless asynchronous transfer (polling,callback) Publish & Subscribe (Pub/Sub) indirect communication over message- oriented Broker connectionless asynchronous transfer (polling,callback)

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Disadvantage MOM incompatible with other Mom implementation Dependent on the MOM vendor for maintenance and future enhancement

Transaction Processing Monitor

Origin of TP Monitors Purpose of TP Monitors What are TP Monitors? What do TP Monitors do? Example of a TP Monitors Features of TP Monitors References

Origin of TP Monitors TP monitor technology emerged 25 years ago when Atlantic Power and Light created an online support environment to share concurrently applications services and information resources with the batch and time sharing operating systems environment.

Purpose of TP Monitors Transaction processing (TP) monitor technology provides the distributed client/server environment the capacity to efficiently and reliably develop, run, and manage transaction applications. efficientlyreliably

What are TP Monitors? A TPM is a standalone program, distinct from the Web server and app server. TP monitor technology controls transaction applications and performs business logic/rules computations and database updates. TP monitor technology is used in data management, network access, security systems, delivery order processing, airline reservations, and customer service

What do TP Monitors do? Its mission is to monitor workflow status for transactions that require multiple steps. The TPM generally has the capability to post alerts and rollback errors or generate compensating transactions when an error occurs.

Examples of TP Monitors CICS (Customer Information Control System) by IBM. TUXEDO by BEA.

Customer Information Control System a family of application servers and connectors that provides industrial- strength, online transaction management and connectivity for mission-critical applications.

Customer Information Control System CICS handles more than thirty billion transactions per day Each day CICS processes more than $1 trillion in transactions More than thirty million people use CICS CICS can support over nine hundred thousand concurrent users

Customer Information Control System CICS supports numerous application development environments and models including COBOL, PL/I, Java, EJB and Object Oriented (OO), in any combination. CICS provides unmatched scalability, performance, throughput, reliability, security and data integrity - all essential for e-business. CICS runs on z/OS, OS/390 and VSE/ESA. CICS API is also available on AIX, Windows NT, Solaris, HP-UX via TXSeries.

TUXEDO BEA Tuxedo is the backbone for enabling transactions that stretch from front-end e- commerce applications to back- office processes, across any system, anywhere in the world.

TUXEDO: Features Business-critical reliability. BEA Tuxedo has been tested and proven in thousands of the most demanding mission-critical applications. Virtually unlimited scalability. As demands increase, additional servers can be added on the fly without disrupting ongoing operations. Simplified development. You can focus on enterprise applications while BEA Tuxedo handles the underlying complexity of distributed applications. Unparalleled high-performance. BEA Tuxedo is designed for large-scale, Web-to-mainframe enterprise solutions.

TUXEDO: Client/Server Model

Features of TP Monitors Load balancing: is a technique used for distributing service requests evenly among servers that offer the same service.

Features of TP Monitors Priorities determine the order in which service requests are dequeued by a server. Priority is assigned by a client to individual services and can range from 1 to100, where 100 represents the highest priority.

Other features of TP Monitors Data compression Data encoding Data encryption Event management Security management

References Customer Information Control System  Tuxedo  Transaction Processing Monitor  TPM TPM Whatis website 

In Summary:  Middleware is essential to migrating mainframe applications to client/server applications and to providing for communication across heterogeneous platforms.  Middleware is sometimes called plumbing because it connects two sides of an application and passes data between them.

Key Words: Middleware TP monitors Message-Oriented Middleware (MOM), RPC systems RPC Object Request Brokers (ORBs) Database access systems

References: umn.html?ArticlelD=93 ddleware.html