Middleware-Based OS Distributed OS Networked OS 1MEIT Application Distributed Operating System Services Application Network OS

Middleware-based OS MEIT2 Application Middleware Operating System Services Networked OS

Generic Middleware Communication stacks for c/s communication Distributed directories for location Authentication services for security RPCs for accessing remote functionalities Queuing services for synchronous & loosely coupled communications. MEIT3

DCE Architecture and Services 4MEIT

Key services Remote Procedure Call Directory service Security service Time service Threading service Distributed File service IDL Compiler Diskless service MEIT5

Directory service Cell Directory Service (CDS) Global Directory Service (GDS) Global Directory Agent (GDA) Directory Service Programming Interface MEIT6

Global Directory Agent (GDA) MEIT7 GDSGDACDS

Directory Service Programming Interface MEIT8 Client Machine Client application CDS clerkCache Server Machine RPC Server Server Machine Clearing house CDS Server

Service-Specific Middleware Needs to accomplish a particular c/s type of service OLTP middleware Communication middleware Object-specific middleware Workflow management middleware Internet-specific middleware MEIT9

Database Middleware Database Middleware provides a common interface between a query and multiple, distributed databases. Using either a hub and spoke architecture or a distributed architecture it enables data to be consolidated from a variety of disparate data sources 10MEIT

Messaging Middleware Common interface and transport between applications. – Stores the data in a message queue if the target machine is down or overloaded – May contain business logic that routes messages to the appropriate destinations and reformats the data as well. – Similar to an messaging system, except that it is used to send data between applications. 11MEIT

Application Server Middleware A Web-based application server that provides interfaces to a wide variety of applications is used as middleware between the browser and legacy systems. – The browser can be used at desktops or on laptops when travelling. – A wide range of server-side processing has been supported by appservers (i.e.;J2EE). 12MEIT

Types of Middleware Services 1.Distributed system services, Critical communications, program-to-program, and data management services. This type of service includes RPCs, MOMs and ORBs. 2.Application enabling services, Access to distributed services and the underlying network. This type of services includes transaction processing monitors and database services such as Structured Query Language (SQL). 3.Middleware management services, Which enable applications and system functions to be continuously monitored to ensure optimum performance of the distributed environment. 13MEIT

Distributed Objects and Distributed Processing Distributed objects have the biggest potential to solve a wide range of challenges faced by designers of large software systems. Some of these challenges include – component packaging, – cross-language interoperability, – interprocess communication, and – intermachine communication. We separate distributed object architectures into two categories: – component architectures and – remoting architectures. Component architectures focus primarily on component packaging and cross-language interoperability. Remoting architectures focus primarily on support for remote method invocation on distributed objects. 14MEIT

Remoting Architectures Open Software Foundation’s (OSF) Distributed Computing Environment (DCE) – which actually is a distributed processing environment based on the Remote Procedure Call (RPC) paradigm (purely procedural) Object Management Group’s (OMG) Common Object Request Broker Architecture (CORBA). – The notion of component packaging and deployment has only recently been added to CORBA MEIT

Component Architectures Microsoft’s Component Object Model (COM) – addresses packaging and deployment of binary component as well as cross-language interoperability JavaBeans and Enterprise Java Beans (EJB) component models introduced by SUN Microsystems. Both, COM and EJB address remoting to some extend: – the COM model has been extended to Distributed COM (DCOM) using an extended version of DCE RPC as transport. – EJB supports client/server communication based on Java Remote Method Invocation (RMI). – RMI is special as it integrates closely with the Java language without requiring a special Interface Definition Language (IDL) to describe component interfaces accessible for remote invocations. In an evolutionary sense, Microsoft’s.NET is the newest and most advanced component architecture available in the market today. 16MEIT