1 CS590L Distributed Component Architecture Yugi Lee STB #555 (816) * This presentation is prepared based on Michael Stal’s COM+, CORBA, EJB Presentations

2 Motivation Driven by the Internet as well as mobile and embedded devices distributed solutions are now considered common place. However, building distributed applications is a non- trivial task. Thus, the question is: how can we efficiently build and deploy such applications? –Basic architectural understanding of OO Middleware. –Better leveraging Component Platforms.

3 Distributed Applications

4 Services of the Middle Tier The services in the Middle Tier participate in different kinds of tasks: –They must participate in the workflow of integrated business processes. –They must connect to databases and other backend systems for data storage and service access.

5 Services of the Middle Tier Problem: Functionality in the middle tier is always subject to change and adaptation. It is used in unforeseen contexts (from different clients). Solution: The middle tier should not be structured as a monolithic unit but rather be decomposed.

6 Component-based Software Components are the appropriate means for decomposition: Presentation Tier components: –they typically represent sophisticated GUI elements. –they share the same address space with their clients. their clients are containers that provide all the resources. they send events to their containers. Middle Tier components: –they typically provide server-side functionality. –they run in their own address space. –they are integrated into a container that hides all system details.

7 Building distributed applications is complex How to cope with heterogeneity? How to access remote services in a location-transparent way? How to handle (de-) marshaling issues? How to find remote objects? How to activate remote objects? How to keep state persistent and consistent? How to solve security issues? Synchronous/ asynchronous communication?

8 Distributed Objects are the answer What we need is an architecture that... –supports a remote method invocation paradigm – provides location transparency – allows to add, exchange, or remove services dynamically – hides system details from the developer

9 Requirements for Distributed Component-based Applications Transparent, platform- neutral communication. Activation strategies for remote components. Non- functional properties such as performance, scalability, Quality of Service. Mechanism to find and create remote components. Keeping state persistent and consistent. Security issues. Data transformation. Deployment and configuration.

10 Component/ Container Approach In order to shield components from the underlying infrastructure specifics, containers are introduced. Containers: –manage components and notify components about events such as activation, passivation, transactions. –provide components access to services such as transactions, security, persistence. –help to register and deploy components.

11 Application Servers (Servers+ Containers)

12 Select the right standard COM+, Windows DNA 2000, Microsoft. NET or CCM (Corba Component Model), CORBA 3 or EJB, J2EE Andrew Tanenbaum: “The best thing about standards is that there are so many to choose from“

13 EJB 2.0 There are three flavors of enterprise Beans: –A session bean type (mandatory for EJB 1.0 and EJB 1.1 compliant containers) –An entity bean type (mandatory in EJB 1.1 compliant containers) –A message bean type (mandatory in EJB 2.0 compliant containers)

14

15 CORBA-3 In the year 2000 the OMG has published CORBA 3 which offers solutions in the 3 areas: –Internet –Quality of Service – Components With CORBA 3, the OMG offers a full range of enterprise technologies. –the specification of CCM (Corba Component Model), 11/2001 –Interoperability (COM, EJB) –Portable Object Adapter (POA)

16 CORBA Architecture

17 COM+ First of all: COM+ = COM + Services COM+ is MTS 3.0 It is integrated to Windows 2000 It contains a lot of services such as –Transaction Serrvices (MTS) –Security Services –Synchronization Services –Queued Components –Event Service –COM+ Catalog = RegDB + Registry

18 COM+ Architecture

19 Middleware Comparision-1

20 Middleware Comparision-2

21 Middleware Comparision-3

22 Middleware Comparision- 4

23 References Henning, Vinoski: Advanced CORBA Programming with C++, Addison- Wesley, Donald Box: Essential COM, Addison Wesley, Chappel, Understanding Windows 2000 Distributed Services, Microsoft Press, Rofail, Shohoud, COM and COM+, Sybex, Buschmann, Meunier, Rohnert, Sommerlad, Stal: Pattern- Oriented Software Architecture - A System of Patterns, Wiley, Schmidt, Stal, Rohnert, Buschmann: Pattern- Oriented Software Architecture 2 – Patterns for Concurrent and Networked Objects, Wiley, Gamma, Helm, Johnson, Vlissides: Design Patterns - Elements of Reusable Object-Oriented Software, Addison Wesley, 1995.