Transcript Slides

CS590L Distributed Component
Architecture
Yugi Lee
STB #555
(816) 235-5932
[email protected]
www.sice.umkc.edu/~leeyu
* This presentation is designed based on Michael
Stal’s COM+, CORBA, EJB Presentations
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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.
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Distributed Applications
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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.
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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.
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Component-based Software
• Components are the appropriate means for decomposition:
• Presentation Tier components:
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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.
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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?
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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
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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.
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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.
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Application Servers (Servers+ Containers)
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Select the right standard
• COM+, Windows DNA 2000, Microsoft. NET or
• CCM (Corba Component Model), CORBA 3 or
• EJB v2, J2EE
Andrew Tanenbaum: “The best thing about
standards is that there are so many to choose
from“
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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)
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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)
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CORBA Architecture
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COM+
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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
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Transaction Serrvices (MTS)
Security Services
Synchronization Services
Queued Components
Event Service
COM+ Catalog = RegDB + Registry
COM+ Architecture
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Middleware Comparision-1
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Middleware Comparision-2
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Middleware Comparision-3
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IIOP: Internet Inter-Orb Protocol, OTS: Object Transaction Services, JTS: Java Transaction Services,
MTS: Microsoft Transaction Services ADSI: Active Directory Service Interfaces
JNDI: Java Naming and Directory Interface AMI: Asynch Messaging Interface
Middleware Comparision- 4
UPnP: Universal Plug and Play
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Universal Plug and Play
• an architecture for pervasive peer-to-peer network connectivity of
PCs of all form factors, intelligent appliances, and wireless
devices.
• a distributed, open networking architecture that leverages TCP/IP
and the Web to enable seamless proximity networking in addition
to control and data transfer among networked devices in the home,
office, and everywhere in between.
• MS XP support for UPnP Internet gateways, providing broadband
users for online games, videoconferencing and other peer-to-peer
services.
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JINI/JXTA
• Jini: an open architecture that enables developers
– to create network-centric services that are highly adaptive to change.
– to build adaptive networks that are scalable, evolvable and flexible as
typically required in dynamic computing environments.
• JXTA:
– a set of open, generalized peer-to-peer (P2P) protocols, defined as XML
messages, that allow any connected device on the network ranging from
from cell phones and wireless PDAs to PCs and servers to communicate
and collaborate in a P2P manner.
– JXTA peers create a virtual network where any peer can interact with other
peers and resources directly even when some of the peers and resources are
behind firewalls and NATs or are on different network transports.
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References
• Henning, Vinoski: Advanced CORBA Programming with C++, Addison- Wesley,
• 1999.
• Donald Box: Essential COM, Addison Wesley, 1998.
• Chappel, Understanding Windows 2000 Distributed Services, Microsoft Press,
2000.
• Rofail, Shohoud, COM and COM+, Sybex, 2000.
• Buschmann, Meunier, Rohnert, Sommerlad, Stal: Pattern- Oriented Software
Architecture - A System of Patterns, Wiley, 1996.
• Schmidt, Stal, Rohnert, Buschmann: Pattern- Oriented Software Architecture 2 –
• Patterns for Concurrent and Networked Objects, Wiley, 2000.
• Gamma, Helm, Johnson, Vlissides: Design Patterns - Elements of Reusable
Object-Oriented Software, Addison Wesley, 1995.
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