Transcript Seminarium on Component-based Software Engineering

Seminarium on
Component-based
Software Engineering
CORBA
Jan Willem Klinkenberg
Object Management Group (OMG)
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Consortium of Computing Industry
Founded in 1989
Non profit
around 800 members
Goal: standardization of “whatever it
takes” to achieve interoperability on
all levels of an open market for
“objects”
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OMG
 Original effort: fix “wiring” problem:
How can distributed object-oriented systems
implemented in different languages and running on
different platforms interact?
Incompatibility between compilers
Differences in object models
Differences in platforms
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Solution:
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CORBA
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CORBA
 Common Object Request Broker
Architecture.
 Open standard
 1991 – version 1.0
 Initial version.
 1995 – version 2.0
 IIOP
 OMA
 More languages support
 2002 – version 3.0
 Corba Component Model (CCM)
 Scripting languages support
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CORBA
 CORBA - Common Object Request
Broker Architecture.
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IDL
 Interface Definition Language
 Defines all object interfaces in a common language
 Bindings are available for C, C++, Java, Python,
Smalltalk, Cobol, etc…
 An IDL compiler generates stubs and skeletons.
 Stubs:
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Looks like local object
Marhals arguments
Forwards all invocations through ORB to target object
 Skeletons:
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Receives invocations from ORB
Unmarshals arguments
Invokes target methods
Sends back return value
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IDL – example
module Example {
struct Date {
unsigned short Day;
unsigned short Month;
unsigned short Year;
};
interface Ufo {
readonly attribute unsigned long ID;
readonly attribute string Name;
readonly attribute Date FirstContact;
unsigned long Contacts();
void RegisterContact(out Date dateOfContact);
};
};
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IDL types
 IDL distinguishes between basic and
constructed type and CORBA object
references.
 Before CORBA 2.3, only references
 Since CORBA 2.3, call by value is
supported -> standard mapping by
XML
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DII and DSI
Sometimes binding can be too static:
 DII Dynamic invocation interface
 DSI Dynamic skeleton interface (since
Corba 2.0)
These interfaces allow for dynamic selection
of methods at client side or server side
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ORB
 Object Request Broker
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Routes the method invocations
Interface repository
Implementation repository
Can load and start object servants
Can communicate with other ORBs using
IIOP
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CORBA and OMG IDL
IDL source
Applications
Programs
Dynamic
invocation
interface
IDL
stubs
IDL
compiler
ORB
interface
Object
servants
IDL
Skeletons
Dynamic
Skeleton
interface
Object
Adapter
Object Request Broker (ORB)
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Object Adapter
 Object servants register with ORB via the
object adapter.
 Servants are loaded and started by ORB via
adapter.
 BOA – Basic Object Adapter
 Under specified, deprecated in 1998
 POA – Portable Object Adapter
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Replaced the BOA
Essential for several CCM features
Creates object references
Several possible policies for object creation
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Server, client or both
 Separation of client and called object
does not impose an asymetric
architecture.
 The same process can issue and
receive calls.
 Pure application programs do not
require registration with ORB
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CORBA v.1 - Problems
 An ORB is essentially an remote
incovation service
 Replaces sockets and remote
procedure calls in distributed
applications with a cleaner model
So what’s the problem?
 Applictions still have to share many
conventions to interoperate
 OMG had to broaden it’s focus.
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OMA - Object Management Architecure
 Since CORBA 2.0
 Adds new areas of standardization:
 CORBAservices
 Common object services e.g.: naming, trader
event, security
 CORBAfacilities – defines a specific component
framework than can be used to integrate
components.
 Horizontal: domain independent, focus on
specific application models e.g. printing facilities
 Vertical: domain specific e.g. healtcare, finance
 Application object specifications (currently void)
 CCM - CORBA Component Model (since 3.0)
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CORBA Services supporting
enterprise distributed computing
 Naming service
 White pages
 Trader service
 Yellow pages
 Event service
 Send event objects from event suppliers to
event consumers.
 Notification service
 Add QoS, filtering, etc. to Event service
 Object transaction service
 Security Service
 Encryption, authentication
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CORBA Services supporting architecture using
fine-grained objects
 Concurrency control service
 Lock and release resources
 Licensing service
 For non-freeware objects
 Lifecycle service
 Creation, copying, moving and deletion of
objects
 Relationship service
 Not used or implemented
 Persistant state service
 Allows storing and retrieving of objects
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CORBA Services continued…
 Externalization service
 Mapping of object into stream and back
 Properties service
 Add/delete and retrieve arbitrary properties to
objects
 Object query service (not implemented)
 Locate object instance by attributes
 Object collections service (not implemented)
 Provides collection types like sets, trees, queues or
lists.
 Time service
 Provides a universal time for the distributed system
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CCM - Corba Component Model
 Introduced with CORBA 3.0 in 2002
 Logical extension of Enterprise
JavaBeans
 Is an architecture for defining
components and their interactions
 Provides a packaging technology
 Provides a container implementation
framework (CIF)
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CCM Component
Component interface
OFFERED
Receptacles
My
Business
Component
Event
sinks
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Event
sources
Attributes
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REQUIRED
Facets
CCM Components features
 Ports
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Facet – provided interface
Receptacle – required interface
Event sources
Event sinks
 Primary keys
 Instance identification for client
 Attributes
 Home interfaces
 Provides factory functionality
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CCM packaging
CCM Assembly
CCM Component
CCM Component
Deployment configuration
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CCM Containers
 Component instances are placed
inside containers:
Home interface
Component C
Callbacks
Home for C
Services
Container
Components interact with POA as well as transaction, security, persistence
and notification services via interfaces on their container
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Components types
 There are different types of
components:
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Service
Session
Entity
Process
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CIF
 Component Implementation
Framework
 Described in CIDL, Component
implementation Definition Language
 Creates programming skeletons that
automate many of the basic behaviors of
components, including navigation,
identity inquiries, activation, state
management, lifecycle management, and
so on.
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Questions?
?
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