Distributed Objects Technologies: .NET and CORBA

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Distributed Objects Technologies.NET and CORBA

• Naim R. El-Far, PhD Candidate
• TA for SEG3202 Software Design and Architecture
  with N. El-Kadri (Summer 2005)
  
• Tutorial 4 of 4 24/6/2005

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About Todays Material

• Some of todays material has been adapted from
  presentations by D. Schmitt of Microsoft, and Dr.
  I. Stoica of UC Berkeley.

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In Perspective

• Client/Server Architecture (Tutorial 1)
• N-Tier Architecture (Tutorial 2)
• Concept of Distributed Objects (Tutorial 3)
• Technologies for Distributing Objects
• Java RMI ? J2EE (Tutorial 3)
• .NET (Todays tutorial)
• CORBA (Todays tutorial)

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.NET Enterprise Vision
UsersAny device,Any place,Any time
Roles/ExperiencesGet the right infoTo the right
userAt the right time
Sales
Customer
Supply
Engineering
Operations
XML Web ServicesIntegrate and orchestrate
business applications and processes
Authentication
Scheduling
Notification
Back OfficeHeterogeneous application and server
infrastructure
Customer Service
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What is .NET?

• A generic term for the MS vision
• The successor to Windows DNA
• Sometimes applied to product names
• Such as Windows .NET Server
• A specific software framework
• Includes a common runtime
• Common across OS and dev language
• Includes baseline dev tools in an SDK
• Includes powerful dev environment
• Visual Studio .NET

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.NET Workings

• An evolution from COM/DCOM ? Windows DNA ? .NET
• Platform-independent
• Internet integration
• Security
• Primary Components
• Common Language Infrastructure (CLI)
  specifications for a runtime environment,
  including a common type system, base class
  library, and a machine-independent intermediate
  code known as the Common Intermediate Language
  (CIL) MSIL.
• Common Language Runtime (CLR) Runtime
  environment to run any CIL code that adheres to
  CLI specs usually through JIT compilation.

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.NET Workings

• All CIL is self-describing through .NET
  metadata.
  
• Language implementation ? CIL ? CLR ? MSIL ? .NET
  languages
  
• .NET assemblies, DLL or EXE for Win32. The .NET
  unit of deployment, versioning and security (64
  bit public/private key).
  
• All code is compiled, not interpreted
• Converted to native machine code at install time
  (via NGEN) or run time (via JIT compiler)
  
• Static code management
• Versioning, localizing, and signing
• Configurable assembly resolver
• Global assembly cache (GAC)
• Dynamic code management
• Memory allocation with garbage collection
• Lifecycle management via reference tracking
• Thread pooling

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.NET Workings

• Fine-grained code access security
• Augments OS security (user credentials)
• Ensures that code only performs operations
  allowed by policies set by user or administrator
  
• Based on code source, publisher signature, and
  other evidence
  
• Flexible deployment
• Simple XCOPY (since not bound to Windows
  registry)
  
• Windows installer
• Auto-deploy (aka no-touch or zero-impact)
• Flexible remoting
• Includes XML/SOAP and binary
• Remoting model is easily extended
• Integrates with web services

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Compilation Execution
AssemblyUnit of deployment, similar to DLL or EX
E with added metadata
Compilation
Saved in cache An assembly can also be pre-compil
ed as part of deployment
Before installation or the first time each method
is called
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CLR Internals
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.NET Structure CLR and Win32 Services
Same class library across all programming
languages
C
VB
J...
Enterprise Services
Connects .NET to COM for transactional
components and other enterprise services
ADO.NET
ASP.NET
CLR
Connects .NET to data providers, including XML
documents
Active Directory
MSMQ
COM
IIS
WMI
Win32
Provides WebForms for thin clients, plus web
services via HTTP
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.NET Framework More generally
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.NET Framework
Internet and Web Services
Other Framework Extensions
Framework Features
Windows Framework Extensions
Standard .NET Framework
Windows
Other OS
Application Reach across Devices
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.NET Mobility Framework
Internet and Web Services
Device Vendor Framework Extensions
Framework Features
Windows CE Framework Extensions
.NET Compact Framework
Windows CE
Other OS
Application Reach across Devices
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.NET on non-MS Operating Systems

• Microsofts Shared Source Initiative
• Rotor Microsoft shared-source version of .NET
  for FreeBSD
  
• Mono Novell (formerly by Ximian) open-source
  version of .NET for GNU/Linux, UNIX, Mac OS X,
  and Windows based computers.
  
• Portable .NET is part of the DotGNU project.

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Introduction to CORBA

• Common Object Request Broker Architecture
  (CORBA)
  
• A standard for software componentry.
• Created and controlled by the Object Management
  Group (OMG).
  
• Defines APIs, communication protocol, and
  object/service information models to enable
  heterogeneous applications written in various
  languages running on various platforms to
  interoperate ? platform and location transparency
  for sharing well-defined objects across a
  distributed computing platform.
• CORBA "wraps" code written in some language into
  a bundle containing additional information on the
  capabilities of the code inside, and how to call
  it. The resulting wrapped objects can then be
  called from other programs (or CORBA objects)
  over the network.
• CORBA can be considered as a machine-readable
  documentation format.
  
• Interface Definition Language (IDL) to specify
  the interfaces that objects will present to the
  world.
  
• A "mapping" from IDL to a specific implementation
  language like C or Java. Standard mappings
  exist for Ada, C, C, Lisp, Smalltalk, Java, and
  Python. There are also non-standard mappings for
  Perl and Tcl implemented by ORBs written for
  those languages.

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High-Level Overview of CORBA

• CORBA applications are composed of objects.
• For each object type you define an interface in
  OMG IDL.
  
• CORBA Separation of interface from
  implementation.
  
• Well-defined, strict interfaces.
• Hidden implementation.
• Clients access objects only through their
  advertised interface.
  

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CORBA Architecture
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Stub

• Provides interface between client object and ORB
  
  
• Marshalling client invocation
• Unmarshalling server response

Server
Client
Java Object
C Object
Skeleton
Stub
Object Adapter
IIOP
ORB
ORB
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Skeleton

• Provides iterface between server object and ORB
• Unmarshaling client invocation
• Marshaling server response

Server
Client
Java Object
C Object
Skeleton
Stub
Object Adapter
IIOP
ORB
ORB
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(Portable) Object Adapter (POA)

• Register class implementations
• Creates and destroys objects
• Handles method invokation
• Handles client authentication and access control

Server
Client
Java Object
C Object
Skeleton
Stub
Object Adapter
IIOP
ORB
ORB
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Object Request Broker (ORB)

• Communication infrastructure sending messages
  between objects
  
• Communication type
• GIOP (General Inter-ORB Protocol)
• IIOP (Internet Inter-ORB Protocol) (GIOP on
  TCP/IP)

Server
Client
Java Object
C Object
Skeleton
Stub
Object Adapter
IIOP
ORB
ORB
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CORBA Object
Server
CORBA Object
Interoperable Object Reference
Interface IDL
C/Java Implementation
Servant
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Example of CORBA Services

• Naming Keeps track of association between object
  names and their reference. Allows ORB to locate
  referenced objects
  
• Life Cycle Handles the creation, copying,
  moving, and deletion objects
  
• Trader A yellow pages for objects. Lets you
  find them by the services they provide
  
• Event Facilitates asynchronous communications
  through events
  
• Concurrency Manages locks so objects can share
  resources
  
• Query Locates objects by specified search
  criteria

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Remote Invocation in CORBA

• Oversimplification
• Client first obtains its object reference (E.g.
  Naming Service and the Trader Service).
  
• Remote invocation local invocation
  substituting the object reference for the remote
  instance.
  
• ORB examines the object reference and discovers
  that the target object is remote ? routes the
  invocation out over the network to the remote
  object's ORB.

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Remote Invocation in CORBA

• In more detail
• IDL ? the client knows exactly which operations
  it may invoke, what the input parameters are, and
  where they have to go in the invocation
  
• IIOP (ORBs may use other protocols)
• Although the ORB can tell from the object
  reference that the target object is remote, the
  client can not.

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Object Invocation Models

• Invocation models supported in CORBA

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Interoperability

• Allow multi-vendor ORB implementations to
  communicate with each other
  
• General Inter-ORB Protocol (GIOP) message types

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Object References

• The organization of an IOR with specific
  information for IIOP

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Secure Object Invocation in CORBA
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CORBA Application

• Define interface using IDL
• Compile interface
• Implement interface
• Instantiate server
• Register object as a CORBA object
• Instantiate client
• Invoke CORBA object
• Example using a Java client and server

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J2EE vs. .NET

• Cola vs. Pepsi
• Are you starting from scratch?
• Are you migrating from a legacy system?
• One day, J2EE and .NET will become legacy
  systems.
  
• Past, Present, and Future.
• Web Services ?? Body Organs
• For more details (a little out of date by
  comprehensive http//www.theserverside.com/articl
  es/article.tss?lJ2EE-vs-DOTNET)
  

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Where does CORBA fit it?

• Purpose of CORBA
• IIOP, a pillar of CORBA
• J2EE support for IIOP
• .NET support for IIOP (IIOP.NET, Janeva)
• CORBA, J2EE, and .NET like everything else, the
  mix depends on your purpose, the past, the
  present, and the future of your system.